INFORMATION TO USERS

This manuscript has been tepmduced from the miuofilrn master. UMI films the

text directly from the original or copy submiüed. Thus, some thesis and

dissertaüon copies are in typvnter face, Aile othen may be fmm any type of

wmputef printer.

The qurlity of mis reproduction b dependent upon the quaMy of the copy

submitted. Broken or indistinct @nt, cobrad or poor quality illustrations and

ptmtographs, pnnt bleedlhrough, substandard rnargins, and impmper alignment

can advenely affect reprodudion.

In the unlikely event that the author did not send UMI a complete manuscript and

there are missing pages, these will be noted. Also, 1 unauthonted copyright

matefial had b be removed, a note witl indicate the deletion.

Ovemire materials (e.g.. maps. drowings, chPrts) are reproduced by sectiming

the original, beginning at the uppr lefthand corner and continuing from left tio

nght in wual with small overlaps.

Photographs induded in the original manusaipt have I#en iepmduced

xefagrsphically in this copy. Higher quality 6" x 9" black and white photographie

pn'nts are available for any photogmphs or illustmtions appearing in this copy for

an additional charge. Contact UMI directly to oder.

Bell 8 Hawell Information and Leaming 300 Norlh teeb Road, Ann Amr, MI 481(361348 USA

Optical Field Response from

S tructured Nano- and Mesocomposites

A thesis submitted to the Faculty of Graduate Shidies and Resenrch in parfitai fuifiUment of the requirernents for the degree of

Master of Science

Department of Chemistry

McGU University

Montréal, Québec, Canada

@ March 1998

National Library (*I of Canada Bibliothèque nationale du Canada

Acquisitions and Acquisitions et Bibliographie Services services bibliographiques

395 Wellington Street 395, rue Wellington ûttawa ON KI A ON4 Otîawa ON K I A ON4 canada Canada

Yow lik vorn r*himœ

Our iVo N a m reimwm

The author has granted a non- exclusive Licence aiIowing the National Library of Canada to reproduce, loan, distribute or sel1 copies of this thesis in microforni, paper or electronic formats.

The author retains ownership of the copyright in this thesis. Neither the thesis nor substantial extracts fiom it may be printed or othenÿise reproduced without the author's permission.

L'auteur a accordé une licence non exclusive permettant à la Bibliothèque nationale du Canada de reproduire, prêter, distribuer ou vendre des copies de cette thèse sous la forme de microfiche/film, de reproduction sur papier ou sur format électronique.

L'auteur conserve la propriété du droit d'auteur qui protège cette thèse. Ni la thèse ni des extraits substantiels de celle-ci ne doivent être imprimés ou autrement reproduits sans son autorisation.

Abstract

Molecular self-assembly (MSA) was used to fabricate multilayered composites on

silicon. silicon monoxide and silica substrates. 3-rnercaptopropyltrimethoxysilane

(MPTMS) was grafted ont0 the substrates, followed by chernisorbed silver colloidal

nanoparticles. 1.4-benzenedimethanethiol (BDMT) was used to chemisorb gold to silver

coiioidal nanoparticles forming an MPTMS-silver-methyl-BDMT-gold heterostmcture. A

self-poling stilbazole dye - (E)-[4-NN-(octadecyImethy1mino)styryl]pyridine (ODMASP) - was integrated with a mercaptoacetic acid (MAA) spacer into an MPTMS-

silver-MAA-ODMASP heterostmcture by MSA of ODMASP C i8 dkyl tails. ODMASP

on fractal silver aggregates enhanced the 2nd-order nonlinear susceptibility irnplying that

silver colloid intensified the electrical field to produce a i2' of 1.48 x c'/J' (4.00 x

IO'* esu). We used x-ray photoelectron spectroscopy (XPS), transmission electron

microscopy (TEM), ultraviolet-visible (UV-VIS) spectroscopy and second harmonic

generation (SHG) for characterization. We describeci the spthesis of a tolane dye - N-4- [ ( 4 ' - n i t r o d i p h e n y l e t h y n y l ) p h e n y l ] - b i s - 2 ' (NDPEPD) - by palladium-

cataiyzed cross-coupling. Corona poled NDPEPD-doped poly(styrene) films produced a

i2' of 1.5 x 1 o - ~ c~/J' (0.4 x 1 O* esu).

Résumé

La méthode de l'auto-assemblage moléculaire a été utilisée pour la fabrication de

composites en multicouches sur du silicium, du monoxyde de silicium, ainsi que sur des

substrats de silice. Le composé 3-mercaptopropyltriméthoxysilane (MPTMS) a été greffé

sur ces substrats, suivi de la chémisorption de monoparticules de colloïdes d'argent. Le

composé 1,4- benzénediméthanethiol (BDMT) a été utilisé pour réaliser la chémisorption

d'or sur des nanoparticules colloïdales d'argent, formant ainsi une hétérostructure de

composition MPTMS-argent-méthyle-BMDT-or. Par ailleurs, un colorant pouvant

aligner son moment dipolaire avec un champ dlecuique, le stilbazole - (a-[4-(NJV-

octadecylméthylamino)styryl]pyridine (ODMASP) - a été inséré à I'aide d'un maillon

d'acide mercaptoacétique (AMA) à l'intérieur de l'hétérostructure MPTMS-argent-

AMA-ODMASP par auto-assemblage moléculaire des chaînes alkyles Cis du ODMASP.

La présence d'ODMASP sur des surfaces fractales d'argent a pour effet d'augmenter la

valeur de i2' (susceptibilité non-linéaire de second ordre), impliquant ainsi que les

colloïdes d'argent intensifient le champ électrique produisant un f2' de 1.48 x 10'" c~/J', soit 4.00 x 10" esu. Les techniques de spectroscopie par photoélectrons-X (XPS), de

microscopie à transmission électronique (TEM), de spectroscopie ultraviolet-visible (UV-

VIS) et de génération harmonique de second ordre (SHG) ont éti5 utilisées pour la

caractérisation des materiaux. La synthèse d'un colorant tolane - N4[(4'-

nitrodiphényléthynylephényle]-bis-2"-dieoe (NDPEPD) - par reaction de

couplage catalysée au palladium a été décrite. Les films à base de poly(styrène) dopes au

NDPEPD donnent un 22ZIZ' de 1.5 x 1 0 - ~ c~/J', soit 0.4 x lu8 esu.

I want to express my gratitude to.. . - Dr. Mark Andrews for his enthusiasm, direction and support during my research - Dr. M. A. (Amir) Fardad for his friendship, encouragement and advice - Dr. Norbert Schühler for his fnendship and support in XPS analyses - Dn. Galina Milova, Ignacio Vargas-Baca, Andrew Brown and Xin Min Du for

their friendship, technical support and assistance - Dr. Georges Veilleux (INRS-UQAM) for XPS data and scheduling - Dr. Hojatollah Vali (Department of Earth and Planetary Sciences - McGill), Mn. Jeannie Mui and Matilda Cheung (Department of Anatomy - McGill) for TEM analyses and photo development

- Dn. Mark Kuzyk and Dennis Garvey (Department of Physics - Washington State University) for technical advice

- Dr. Fassil Ghebremichael (US Air Force Academy) for technical advice - Dr. Ashok Kakkar for his advice and support conceming SHG analyses - Drs. George Wong and Jianyao Wu (Materials Research Center, Department of

Physics and Astronomy - Northwestem University) for SHG analyses - Ms. Renée Charron for rnanaging my academic accounu - Emmanuelle for the abstract translation, Lu, Benji, Kevin, Tony for organic

syntheses; Jean and Wenbo for colloid syntheses, Nadim for MS analyses, Ed (Department of Chernical Engineering - McGill) for elemental analyses

- Kalai, James, Max and al1 lab colleagues (Photonic and Polyrneric Materials Research Group - McGill) and Sara, Peyman, Zakaria (Photonics Research Group - École Polytechnique de I'Univenite de Montréal) for their friendship and support

- the following people for friendship, advice and support.. . - William and Vivian, Hany and E.J., Jeff, Chris and Cindy, Amber, Jill, Cathy, Thomas,

Redina, Sam, Kelly and Sonia, Jay, George, James - Maria, Melanie, Gabriel and Linda, Tony, Grant and Francine, Paul, Tem, Myriam, Glen, Sharon, Eric, Nathalie, Tara, Kohei, Frank, Dam, Sherril, Jean-Claude

- Tina, Donna, Giovanna, Elana, Marianne, Eleanor, Paule - GCrard, Christophe, Bianca, Tobi, Kevin, Annie, Maria, Sung Dae, Jung, Josh,

Mariah, lennifer, Caroline, Soraya, Katie, Beth, Annette, Paul, Brian G., Man, David, Martin, Vickie, Karen, Jenny, Elsah, Hannah, Louis, Albert, Brian H

- Rania, Ngiap Kie, Shane, loy, Shanti, Christine, Kui, Carl, Matthew, Neil, Luc, Leujun, Maria, Hongwei, Daniel, Stephanie, Heather, Clare, Lana, Xiao Ming

- al1 the other professors, staff members and studenu at McGill who assisted me

Most importantly, 1 want to thank God, my farnily and all my fnends at home, especially Mom and Dad, Jan, Jeff and JO-Dee for al1 their love and support, encouragement and advice during my studies in Montréal.

Table of Contents

Abstract R6sumé Ackno w ledgrnents Table of Contents List of Tables List of Figures List of Abbreviations

Chapter 1

General Introduction

1.1.1 Overview 1.1.2 Molecular Self-Assembly (MSA) 1.1.3 Nonlinear Optical Organic Dyes 1.1.4 Optical Field Enhancement 1.1.5 Research Applications

Chapter 2

Introduction

2.1.1 Multilayered Composite Materials

2.2.1 Silver Colloid Hydrosol 2.2.2 Gold Colloid Hydrosol 2.2.3 MPTMS Organic Graft 2.2.4 Silver Nanoparticles 2.2.5 Methylation of MPTMS 2.2.6 MAA and BDMT Organic Spacen 2.2.7 Gold Nanoparticles 2.2.8 ODMASP Organic Dye 2.2.9 ODMASP in Poly(styrene) 2.2.10 Characterization

1 *.

11 .*. 111

iv vi

vii

Resuits and Discussion

2.3.1 X-ray Photoelectron Spectroscopy (XPS) 2.3.2 Transmission Electron Microscopy 2.3.1 Ultraviolet-Visible (W-VIS) Spectroscopy 2.3.2 Second Harmonic Generation (SHG)

Conclusions

Chapter 3

Introduction

3.1.1 NLOD Alternative - NDPEPD 3.1.2 NDPEPD Tolane Dye S ynthesis

3.2.1 PD and IPTE - Aryl Iodide Synthesis 3.2.2 NEDPA - Aryl Alkyne Spthesis 3.2.3 PD and IPTE with NEDPA - Palladium-catal yzed Cross-coupling 3.2.4 NDPEPD - Direct Thiolation 3.2.5 NDPEPD in Poly(styrene) 3.2.6 Chamcterization

Results and Discussion

3.3.1 Synthesis - NDPEPD 3.3.2 Cornparison - NDPEPD versus ODMASP

Conclusions

A. 1 Units Conversion A.2 XP Spcu?il Data

Table 1. I : Donor-acceptor systems

Table 1.2: Linear-nonlinear optical applications

Table 1.3: Poynting vector showing metai nanoparticle in electromagnetic field

Table 1.4: Cornparison of different scales of matter

Table 2.1 : MPTMS-silver-meth y 1-BDMT-gold heterostmcture on silicon wafer

Table 2.2: Elernental binding enrgy - MPTMS-silver-methyl-BDMT-gold heterostructure

on silicon wafer

Table 2.3a: MPTMS-methyl-silver-BDMT-gold heterostructure on silica glas slide

Table 2.3b: MPTMS-silver-MAA-ODMASP heterostructure on silica glas slide

Table 2.4: i2' - MPTMS-silver-MAA-ODMASP, MPTMS-silver and PS-DMASP

heterostructures

Table 3.1 : MAA and ODMASP - solvent, pH and temperature

Table 3.2: An, and P - tolane derivatives

Table 3.3: A.- and - stil bazole derivatives

Table 3.4: i2' - NDPEPD and DMASP in poly(styrene)

Table A- 1 : Unit Conversions

Table A-2: SHG measurements for MPTMS-silver-MAA-ODMASP, MPTMS-silver and

PS -DMAS P heterostructures

List of Figures

Figure 1.1 : Electrical field poling in doped NLOD polymers

Figure 1.2: Second harmonic generation (SHG)

Figure 1.3: Metal nanoparticle in electrical field (at Frohlich frequency)

Figure 2.1 : Schematic - MPTMS-silver-methyl-BDMT-gold heterostnicture on silicon

wafer and silicon monoxide grid

Figure 2.2: Schematic - MPTMS-silver-MAA-ODMASP composite on silica glass slide

Figure 2.3: Glass reactor vesse1 with silica glass slides in PTFE support rack

Figure 2.4: Fiowsheet - MPTMS-silver-methyl-BDMT-gold on silicon wafer and silicon

monoxide grids

Figure 2Sa: TE micrograph - MPTMS-silver heterostmcture on silicon monoxide grid

(82500 X magnification)

Figure 2.5b: TE micrograph - MPTMS-silver-methyl-BDMT-gold heierostructure on

silicon monoxide grid (82500 X magnification)

Figure 2.5~: TE micrograph - MPIhlS-silver-methyLBDMT-goid heterostmcture on

silicon monoxide grid (165000 X magnification)

Figure 2.6a: Histogram - silver nanoparticle size distribution

Figure 2.6b: Histogram - gold nanoparticle size distribution

Figure 2.7a: Logarithmic plot - silver nanoparticle h t a l dimension

Figure 2.7b: Logarithrnic plot - gold nanoparticle fractal dimension

Figure 2.8: Flowsheet - MPTMS-silver-MAA-ODMASP heterostnicture on silica glas

slide

Figure 2.9a: UV-VIS spectrurn - gold + BDMT (in solution)

Figure 2.9b: UV-VIS spectrurn - MPTMS-silverlgold-BDMT on silica glass slide

Figure 2.9~: W-VIS spectnim - MPTMS-silver-BDMT on silica glass slide

Figure 2.9d: UV-VIS spectrurn - MPTMS-silver-methyl-BDMT-gold on silica g l a s slide

Figure 2.10: ODMASP charge transfer between PR* States

Figure 2.1 1 : ODMASP chernisorbed onto MAA (acid-base)

Figure 2.12: W-VIS spectra - MPTMS-silver-MAA-ODMASP composite

Figure 2.13: ODMASP resonance (fundamental and second barmonic frequency)

vii

Figure 3.1 : Schematic - NDPEPD synthesis

Figure 3.2: Schematic - NDPEPD direct thiolation

Figwe 3.3: M>PEPD ground and excited (R-n*) states

Figure 3.4: ODMASP ground and excited (n-n*) states

Figure 3.5: NDPEPD and ODMASP orbital configurations

Figure 3.6: W-VIS spectnim - NDPEPD tolane in methanol

Figure A- l(contro1): XP spectrum - MPTMS + gold (Control)

Figure A-la: XP spectrum - MPTMS (exposed to air) (Sample A)

Figure A-lb: XP spectrum - MPTMS (unexposed to air) (Sample B)

Figure A-lc: XP spectrum - MPTMS-methyl (Sample C)

Figure A-Id: XP spectrum - MPTMS-methyl-silver (Sarnple D)

Figure A-le: XP spectnim - MPTMS-silver (Saniple E)

Figure A- I F: XP spectmm - MPTMS-silver-meth yl-gold (Sarnple F)

Figure A- 1 g: XP spectrum - MPTMS-silver-me th y l-BDMT (Sampie G)

Figure A-1 h: XP spectrum - MPTMS-silver-methyl-BDMT-gold (Sample H)

Figure A-Z(contro1): XP (S 2p) spectnim - MPTMS + gold (Control)

Figure A-2a: XP (S 2p) spectrum - MPTMS (exposed to air) (Sample A)

Figure A-2b: XP (S 2p) spectmm - MfTMS (unexposed to air) (Sample B)

Figure A-2c: XP (S 2p) spectnirn - MPTMS-mer h y1 (Sample C)

Figure A-2d: XP (S 2p) spectmm - MP'I'MS-merh yl-silver (Sample D)

Figure A-2e: XP (S 2p) spectrum - MPTMS-silvcr (Sample E)

Figure A-2f: XP (S 2p) spectrum - MPTMS-silver-methyl-gold (Sarnple F)

Figure A-2g: XP (S 2p) spectnrm - MPTMS-silver-methylBDMT (Sample G)

Figure A-2h: XP (S 2p) spectmm - MPTMS-silvcr-methyl-BDMT-gold (Sample H)

Figure A-3h: XP (Ag 3d) spectrum - MFTMS-si l ver-methyl-BDMT-gold (Sarnple H)

Figure A-4f: XP (Au 4f) spectrum - MPTMS-si1 ver-methyl-gold (Sample F)

Figure A-4h: XP (Au 4f) spectrum - MP'ïMS -s i : v er-methyl-BDMT-gold (Sarnple H)

List of Abbreviations

BDMT - t ,&benzenedimethanethiol BDT - I ,4-benzenedithiol

DMAP - 4iiimethylaminopyridine

DMASP - (E)-[4-(Nfl-dimeth ylamino)] styrylp yridine

'H NMR spectroscopy - proton nuclear magnetic resonance spectroscopy

PD - 4-iodophenyl-bis-2'-diethylethanoatylamine

PTE - 4-iodophenyl-bis-2'-(tert-butyldimethylsilylo~y)e~yl~ne LR - Lawesson's Reagent

MAA - mercaptoacetic acid

MPTMS - 3-mercaptopropyltrimethoxysilane MS - mass spectrometry

MSA - molecular self-assembly

NEDPA - 4-nitro-4'-ethynyldiphenylacetylene NDPEPD - N4[(J'-ni~odiphenylethynyI)phenyI]-bi~-Z'-diethanethioIarnine NDPEPPD - N4[(4'-nitrodiphenylethynyl)phenyl)phenyl]-bi~-2'-die~yle~moatyl~ne

NDPEPPTE - N - 4 - [ ( 4 ' - n i t r o d i p h e n y l e t h y n y 1 ) p h e n y l ) p ~ y l -

sily1oxy)ethylarnine

NLOD - nonlinear optical dye

OCB - optical chernical bench

ODM ASP - (E)-[4-(N&-octadecylmethylamino)s~l]pyridine PDEA - N-phenyldiethanolamine

PMT - photomultiplier tube

PS - poly(styrene)

F E E - poly(tetrafluoroethy1ene) gITPP - palladium tetra(tripheny1phosphine)

PDCDPP - palladium dichlomdiphenylphosphine

SHG - second hatmonic generation

TBA- AF - tetrabuty lammonium chlorideff luoride

TBDMS - tert-butyldimethylsilyl

TEM - transmission efectron microscopy

TMAF - tetramethylammonium fluoride

UV-VIS spectroscopy - ultraviolet-visible spectroscopy

XPS - x-ray photoelectron spectroscopy

" To solemnize this &y the glorious Sun

Stqs ni his course, and p l 9 the a l c h i s r ,

Turning, with qdendour of his precious eye,

nie meagre cloddy earth to glittertng gold. "

King Philip of France - King John, Act III, Scene 1.

William Shakespeare ( 1 564- 16 16)

Chapter 1

General Introduction

Photonic materials are central to the research desdbed in this thesis. Photonics requires

opticai input/output processes using photons instead of electrons.' In photonic materials

chemistry, we endeavor to undentand submicron level events that describe the nature of

material optical properties. Among these properties is optical nonlinearity, which is of

scientific and technoiogical interest? We investigate optical nonlinearity in some detail

later (see Section 1.1.2).

In this thesis, we explore methods to chemisorb colloidal metal nanoparticles onto

various silicon-based surfaces by covalent bonding to organic 3-mercaptopropyl-

trimethoxysilane (MPTMS), grafted ont0 the glass. We select metal particles with

diameters on the order of 4.5- 16.25 nm to intensify laser optical field interactions,

panicularly at the metd plasma frequency. We investigate the possibility of enhancing

the optical nonlinearity of nonlinear optical dyes (NLODs) chemisorbed ont0

nanoparticle surfaces.

This thesis establishes protocols to chemisorb metal nanoparticles to opticd waveguide

surfaces. These surfaces include silicon wafer, silicon monoxide coated TEM grids and

silica glas slides.

Accordingly, the objectives of this thesis are as follows:

1) To assemble nano- and mesoscale multilayered composites composed of silver and

gold nanoparticles. organic spacers and NLODs (ODMASP stilbazole),

2) To demonstrate that gold nanoparticles can be chemisorbed onto silver. selectively.

3) To illustrate 22' enhancement of an NLOD (ODMASP stilbazole) fkom silver

nanoparticles on an optical cheMcal bench (OCB),

4) To synthesize a novel NLOD (MIPEPD tolane) that chemisorbs onto silver or gold

nanoparticle surfaces.

In Section 1.1.2, we provide a definition of molecular self-assembly with examples.

Section 1.1.3 follows with a brief review of the linear and nonlinear optical response of

organic NLODs. We then describe in Section 1.1.4 the enhancement of the local

electromagnetic field sunounding an isolated metal particle where we allude to

ODMASP local field enhancement h m silver surface plasmons. Finally, Section 1.1.5

diagrams the modified OCB waveguide required to perform our f 2 ) nonlinear optical

measurements and outlines the applications of our research.

in Chapter 2, we outline 2 main types of multilayered composites with organothiol

spacers 1,4-benzenedimethanethiol (BDMT) and mercaptoacetic acid ( M M ) .

1) MPTMS-silver-methyl-BDMT-gold heterostmcture on silicon wafer, silicon

monoxide @ds and silica glass slides.

2) MPTMS-silver-MAA-ODMASP heterostnicture on silica glas slides.

We anaiyze the rnultilayer growth sequence of silver-BDMT-gold by XPS and TEM and

compare W-VIS and ft'" nonlinear optical responses fiom SHG in the MPTMS-silver-

MAA-ODMASP heterostrucnire. In Chapter 3, we describe the synthesis of an M D D

(NDPEPD tolane) that chemisorbs ont0 silver without the use of an MAA spacer. We

compare i2) of both doped ODMASP and doped NDPEPD in poly(styrene) or

PS-ODMASP and PS-NDPEPD composites.

1.1.2 Molecular Self-Assembly (MSA)

Ordered organic thin films show considerable scientific and technological promise.

Several examples include thin-film optics, sensors and tramducers, photoresists and

surface coatings (for lubrication, adhesion and ~ e t t i n ~ ) . ~ These applications require

ordered patteming of molecular layers on the surface. Ordered monolayen can arise by a

process termed molecular self-assembly (MSA), which may involve the adsorption of

alkyl acids, alkylthiols or alkylchlorosilanes on noble rnetals such as silver, gold and

oxides such as silica4 In Our research, we use ordered monolayen to constmct intricate

multilayered heterostructuns. MSA exploits the chemical interactions between the

molecular adsorbate and the substrate so that spontaneous assembly occun. Chernical

kinetics and themodynarnics control the rate and stability of an assembled structure.

Ordering in monolayers increases with dkyl length. Hydrophobie alkyl tails of at Ieast

C12 assemble easily in a tram configuration.' Adsorption cnergy increases linearly with

alkyl Iength as described b y

where -A& is the adsorption free energy, - d e h is the adsorption free energy per

methylene group, Nc is the number of carbons in the alkyl and W is the energy per

methylene group.6 The typical adsorption energy for alkylthiols is approximately 750

1mo1-' per methylene group. We focus on chemical adsorption or chernisorption of

organothiols ont0 metal surfaces using MSA. Assembly of organothiol on silver and gold

metai d a c e s has k e n previously reviewed?

In out research, we exploit MSA to self-pole ODMASP and fonn an ordered structure.

We use MSA to promote the self-poling of ODMASP required for second hannonic

generation (SHG). MSA requins no electrical poling to dign ODMASP dipoles since we

exploit the favorable themodynamics associated with the ordering of hydrophobie Ci8

alkyl tails. We pursue the origin of SHG in the following section.

1.1.3 Nonünear Optical Organic Dyes

Nonbear Optics

Nonlinear optical processes depend on microscopic (molecular) and mucroscopic (buik)

polarizability of matter.

(i) Microscopic PolPrizPbüity

At the microscopic level. the poiarizabiiity, pi, of a medium cm be represented by a

Taylor series expansion?

where a,, fijk and are the linear polarizability, fint and second hyperpolarizability

tenson, respectively (in the molecular frame of reference, i-j-k). These tensors relate the

induced polarization, pi, to the electrical field components, Ei, E,, Ek and El.

(ü) Macroscopic Polarizabüity

At the macroscopic level of bulk matter, the polarizability of a medium P I , is similarly

exprcssed as a Taylor series expansion?

nd rd where if)!,, i2)IJx and i3)[ja are nonlinear susceptibility tensors of 2 , 3 and 4' rank.

These tensors relate the induced polarization, PI, to the electrical field components Ei, E,,

Ek and El. E represents the electrical field of a plane of light that may be expressed as

E = Eocos(an), where o represents the electricai field frequency and t represents time?

The l t , 2nd- and 3dsrder nonlinear susceptibilities are related to Eo cos(a*), Eo cos(2air)

and Eo cos(3@), respective1 y.

Even-ordered ternis of the nonlinear susceptibility ~ 2 ' I J f i i 4 '~ ,~ , ...) are non-zero only

for anisotropic media (noncentrosymmetxic - with no inversion center). Nomally, we

nquire electrical field poling to achieve i2' for noncentrosymmetry. Otherwise,

centrosymmetric dye dipoles would cancel and, therefore, /3= O and i2' would not exist.

We use electrical poling by electrical point corona discharge to dign dipoles in the PS-

ODMASP and PS-NDPEPD composites while we simultaneously monitor XI2' using

SHG analYsis.'O

Heating is supplied until temperatures graduaily approach the polymer glass transition

temperature, Tg, or the polymer softening temperature (see Figure 1.1). Polymer softening

allows ODMASP or NDPEPD dipoles to align (by rotation and translation in the polymer

matnx) under an applied electrical field. Dipoles continue to align until the Tg is reached.

Afterwards, the temperature is gradually decreased to room temperature with the applied

field on. These dipoles now remain aligned or poled inside the cooled and hardened

pol ymer.

increase temperature

poling

T<T,

decrease temperature

Figure 1.1: Electrical field poling in doped NLOD polymers

As described in Section 3.2.6, we use corona discharge poling in our PS-ODMASP and

PS-NDPEPD composites to align dipoles. However, we may completely circumvent

elecûical poling by nsorting to MSA. We chwse to use self-poling ODMASP to align

ODMASP diples on a silver nanoparticle surface without the electrical poling

cequirement. By self-poling, we obtain noncentrosymmetry and thus, may measure f2' .

In this thesis we are interested in SHG processes. Optical SHG is a nonlinear optical

process that converts photons at frequency a, to produce one photon at ftequency 2a.

Figure 1.2 diagrams the frequency conversion.

Figure 1.2: Second harmonic generation (SHG)

201

dl

In particular, we are interested in SHG at the silver-ODMASP interface on our

multilayered silica glass slide composites.

nonlincar opticai medium

Orgaaic Dyes

For practical applications. organic NLODs should have environmental thermal stability

and no loss of polar orientational order. Moreover. NLODs must be processible to gain

acceptance in optical device applications. Organic ODMASP and NDPEPD are of

interest since they filfi11 these materials desiderata. In addition, improvements in

molecular design and synthesis inspires us to use ODMASP and NDPEPD.

In ODMASP and NDPEPD. nonlinear optical effects originate in donor-acceptor charge

transfer interactions." Donor functional groups donate electron density and acceptor

hinctional groups accept electron density to polarize the dipole asymmetrically

(polarization in opposite directions). A conjugated carbon structure mediates electron

charge m s f e r through pn-electron orbital delocalizations. Table 1.1 lis& typical donor-

acceptor s ystems.

Table 1.1

Donor-acceptor systems (reproduced from Nalwa et al. 12)

- -- - -

Donor px-structure ~cceptor

m2, mCH3, benzene NOz, NO, CN. OOH, N(w312, m, azobenzene COO-, CONH2, N2H3, Ft Cl, Br, 1, s tilbazole CONHR. CONR2, SH, SR. OR, CH3, tolane CHO, SSI, S02R, OH, NWCOCH3, biphen y1 so2c3F7, s-3.

OCH,. SCH3, benzy lidene COR, COCF3, CF3. oc6k c(cH3)3, polyene COCH3, H=C(CN)2,

COOCHs, O-, S' and C2(CN)3, SaNH2, aromatic N2'. W+, N(CH3);.

and aromatic

Many donor-acceptor systems exhibit optical nonlinearity that has potential in optical

device applications. Outiined in Table 1.2 are relevant examples.

Table 1.2

Linear-nonlinear optical applications (reproduced from Chemla and zysd3)

Order Macroscopic Polarizability Effects Application susce~tibilitv

1 %lfj a re flection optical fibers

2 0' f l second hannonic fnquenc y doublers generation

w+a,+2cu

frequency rnixing optical mixers ar *@ + 0 3

parme tric opticai pararnetric amplification oscillators a 3 + @I + cuz

Pockels effect electro-optical c l l + o + w modulators

Y 4-wave mixing Raman coherent spec troscop y

phase gratings reai time holography

Kerr effect ultra-high speed optical gates

optical bistability amplifiers, amplitude choppers, logic gates

1.1.4 Optical Field Enhancement

Experiments enhancing optical field interactions are well hown. These experiments have

used surface-enhanced Raman scattenng (SERS)'~ and surface-enhanced second

harmonic generation (SESHG)" with noble metal nanoparticles and films. It is

ceasonable to assume that optical fields derived from these metals may enhance the

2"-order susceptibility of ODMASP. Noble metals such as silver and gold may enhance

the optical field by exciting intense nonlinear sources near the metd surface. These

nonlinear sources are due to surface plasmons. In principle, surface plasmons are

responsible for a large electromagnetic field confined to the silver interface. A surface-

propagating mode radiates a nonlinear polarization field. This surface mode may be used

to increase the local fields near an organic dye such as ODMASP, and therefore, the i2' nonlinear optical susceptibility as well. We describe these surface plasmons and local

fields in the following section.

Local Field Factors

We may show that local field factors contribute to increase the i2' optical nonlinearity.

Initially, we cm associate local field factors and optical nonlinearity in the following

equations.16 We may relate the 1"-order nonlinear susceptibility, fi', to the microscopic

polarizability, a, through

2" = NaFIFI 141

where N is the NLOD number density and FI and FI are the local field factors. The local

field factors are tenson in the buik hune of reference. IJ-K. Similarly, we can relate the

2"d- and 3%rder nonlinear susceptibilities, i2', and i3), to the lst- and 2d-order

rnicroscopic hyperpolarizabilities, fl, and y, respectively, through

We note that the local electrical fields, FI, F,, FK and FL, differ from the applied field, E.

These local fields arise from 2 sources: the applied field and the field generated by the

dye that is polarized by the applied field. Therefore. the fields FI and E, are reiated to Lu

by

where LIJ is the 2nd-rank local field tensor, FI is the local field and EJ is the applied field.

From standard micro- and macroscopic nonlinear susceptibility equations, it can be

shown that

f $k = dVP',d) 181

where N is the dye nurnber density and ('2'qk is the znd-order local field susceptibility for

k2'. The tensor function <''k may be described according to

<"& = (Lt, j* ,Ljj;&*)}f2'i ,2.

where the exponential function i2' depends on the local field ten SOB Liie ,Lj* and Lu*. We

see therefore, that the bulk nonlinear susceptibility is a strong function of the local field

tenson. Thus, i2' increases by the 3d power. Therefore. small increases in ODMASP

local fields c m result in large increases in i2'. Thus, we may enhance the optical

nonlinearity of the silver-ODMASP composites through a local field effect.

Surface Plasmons

The way that surface plasmons at a metal surface can be used to enhance ODMASP local

fields is discussed in this section. Quantum mechanics describes surface plasmons as

quantized electmmagnetic plasma waves that arise from resonant couplings with the

conduction electron gas or plasma (quanta of free electrons) oscillation^.'^ Classical

mechanics describes a surface plasmon in terms of a simple hannonic oscillator

approximation.

With the Drude model. we may represent the optical behavior of a free electron metd by

where E is the dielecbic function with plasmon frequency, q,, and damping factor, y.

We defined the plasma frequency through a+2 = fVe2/ma, where N is the number density

of free electrons and m is the effective mass of an electron. Longitudinal electrical field

oscillations occur when d = q,2 and da) = O. These oscillations result from

electrornagnetic fields interacting on the surface of the metai. Figure 1.3 depicts the

Poynting vector that represents the magnitude and direction of the rate of transfer of

electrornagnetic energy around a metal pariicle.'8 At the surface plasmon energy, field

lines distort near the metal particle. The distorted field increases the electromagnetic field

emanating from the particle surface. ~ i e ' ~ first analyzed linear optical responses of metal

nanoparticles. Mie theory accounts for light absorption and scattering from particles

under applied fields. Typically, gold hydrosols show surface plasmon absorbance, where

gold nanoparticles (eu. 5.2-20 nm particle diameter) have a maximum absorbance (ca.

520 nm)?' In addition, silver hydrosols ai about 410 nm aiso show a surface plasmon

absorbance (ca. 8-10 nm particle diameter) have a maximum absorbance (CU. 410 nm).*'

These nanoparticles may be integrated with molecular NLODs to form assembled

multilayers. We describe the applications of multilayered composite films in the

following section.

Figure 13: Poynting vector showing a metai nanoparticle in an electrornajpetic field

1.1.5 Research Applications

Ordered multilayered composite films ranging in thickness from a few nanometers (a

monolayer) to several hundred nanometers. show considerable technological promise.

Electronic and optical devices presently incorporate structures that are in this range.

Composite film heterostnictures have been proposed to replace both passive and active

components traditionally fabncated with other materials. Some applications include

optical waveguides, sensors, detectors, displays and photoresists.? In order to fabricate

these devices, we need to draw upon 2 emerging field disciplines - materials chemistry

and photonics.

Nano- and M e s o d e

Our intenst is to develop composite heterostnictures from nano- and mesoscale matter.

Nanoscale structures or nanostructures occupy nanometer scale dimensions of 1 - 100 nm.

Similarly, mesostructures occupy nanometer scale dimensions of 10' nm (approximately

100-500 nm)? Figure 1.4 classifies these dimensions. Materials chernistry allows us to

manipulate and construct matter using the "tools" of MSA (see Section 1.1.1). Now, we

may see how MSA may be used to fabricate nano- and mesoscale matter. In the present

research, we use MSA to assemble nanoscale ODMASP and NDPEPD into multilayered

heterostructures. Colloidal nanoparticles occupy mesoscale dimensions and are

chemisorbed onto grafted MPTMS

) Nanoscale Mesoscale Microscale Macroscale I

1 - 1 0 nrn - 100 nm ci~un 1 p l 0 mm

Figure 1.4: Cornparison of different scaies of matter

OpticaI Chernid Benches

Chemical surface reactions cm be probed by combining techniques of integrated optics

with surface spectroscopy. To do so we use microscopic laboratories (optical chernical

benches or OCBs) where we combine the chemical and spectral domains by carrying out

research in both using an optical waveguide. In fact, the OCB is a modified waveguide,

whose surface acts as a "benchtop" to perform chemical reactions involving assembled

nano- and mesostructum. Figure 1.5 shows an OCB acting as an opticai waveguide with

n, representing the waveguide substrate and ni repnsenting the optical film composite.

Total internai reflection occurs inside the wavepide." At the film-substrate interface el > sin"(nrhz) and at the air-substrate interface 6 > sin-'(n3/n2).

Figure 1.5: Opticai Chemical Bench Waveguide

References

' B. E. A. Saieh, M. C. Teich, Fundamentols of Photonics, Wiley, New York, 1991, pp.

238-26 1.

* (a) D. J. Williams, Ed., Nonlinear Optical Properties of Organic and Polymeric

Materials, ACS Symposium Series 233, Amencan Chemical Society, Washington, DC,

1983; (b) S. R. Marder, J. E. Sohn, G. D. Stucky, Eds., Materials for Nonlinear Optics:

Chemical Perspectives, ACS Symposium Series 455, Amencan Chemical Society,

Washington, DC, 199 1.

(a) L. Netzer, J. Sagiv, J. Am. Chem. Soc. 105,674-676 (1983); (b) M. Pomerantz, A.

Segrnulier, L. Netzer, J. Sagiv, Thin Solid Films 132, 153-162 (1985); (c) R. Maoz, J.

Sagiv, Langmuir 3, 1034-1044 (1987); (d) G. M. Whitesides, J. P. Mathias, C. T. Seto,

Science 254, 13 1 2 ( 199 1 ); (e) J. -M. Lehn, Supramolecuhr Chemistry - Concepts and

Perspectives. VCH, Weinheim, Gemany, 1995, pp. 1-8; (f) G. A. Ozin, Adv. Mater. 4,

612 (1992).

(a) S. R. Wasserman, Y. -Tg Tao, G. M. Whitesides, Langmuir 5.10744087 (1989); (b)

D. A. Stenger, J. H. Georger, C. S. Dilcey, J. J. Hickman, A. S. Rudolph, T. B. Nielsen,

S. M. McCon, J. M. Calvert, J. Am. Chem. Soc. 114,8435-8442 (1992); (c) 2. Yang, H.

Yu, Adv. Mater. 9, 5 (1997).

(a) S. H. Chen, C. W. Frank, Langmuir 5,978 (1989): (b) A. Badia, S. Singh, L.

Demers, L. Cuccia, G. R. Brown, R. B. Lennox, Chem. Eur. 5 . 1 3 (1996).

A. W. Adamson, A. P. Gast, Physical Chernistry of Surfoces - 6Lh M., Wiley, New

York, 1997, pp. 392. 7 (a) C. B. Bain, E. B. Troughton, Y. -T. Tao, J. Evall, G. M. Whitesides, R. G. Nuzzo, J.

Am. Chem Soc. 111,321 (1 989); (b) A. Umm, J. Mat. E. 11,205 (1 989).

P. N. Prasad, D. J. Williams, Introduction to Nonlinear Optical Effects in Molecules a d

Polymers, Wiley, New York, 199 1, pp. 1 - 10.

R. Dorn, D. Baums, P. Kersten, R. Regener, Adv. Mater. 4.7-8 (1992).

'O (a) G. R. Mendith, T. G. van Dusen, D. J. Williams, Macromlecules 15,1385 (1982);

(b) J. E. Sohn, K. D. Singer, S. J. Lalama, M. Kuzyk, Polym. Mater. Sci. Eng. 55,532

(1986).

" (a) L. -T. Cheng, W. Tarn, G. R. Meredith, G. L. J. A. Rikken, E. W. Meijer, SPIE Proc. 1147,61-72 (1989); (b) L. -T. Cheng, W. Tarn, S. H. Stevenson, G. R. Meredith,

G. Rikken, S. R. Marder, J. Phys. Chem 95, 1063 1 - IO643 ( 199 1); (c) L. -T. Cheng, W.

Tarn, S. R. Marder, A. E. Steigman, G. Rikken, C. W. Spangler, J. Phys. Chem. 95,

10643-10652 (1991). 12 H. S. Nalwa, S. Miyata. Eds.. Nonlinear Optics of Organic Molecules and Polymers,

CRC Press, New York, 1997, pp. 98.

'%. S. Chemla, J. Zyss Eds., Nonlinear Optical Properties of Orgunic Molecules ami

Crystais, Vols. 1-2, Academic Press, San Diego, CA, 1987, pp. 1-35.

I4 J. Baldwin, N. Schühler, 1. S. Butler, M. P. Andrews, Lungmuir 12,6389-6398 (1996).

'' A. C. R. Pipino, R. P. Van Duyne, G. C. Schatz, Phys. Rev. B 53.7 (1996).

I6 D. J. Williams, Angew. Chem. Int. Ed. Engl. 23,690-703 (1984).

l7 (a) F. Hache, D. Ricard, C. Flytzanis, J. Opt. Soc. Am. B3, 1647 (1986); (b). J. Haus,

R. Inguva. C. Bowden, Phys. Rev. A 40,5729 (1989): (c) J. Haus, N. Kalyaniwalla,

R. Inguva, M. Bloemer, C. M. Bowden, 3. Opt. Soc. Am. B 6.797 (1989); (d) D.

Ricard, P. Roussignol. C. FIytzanis, Op?. Lea 10,s 1 1 (1985); (e) D. Stroud, P. Hui,

Phys. Rev. B 37,8719 (1988).

C. F. Bohren, D. R. Huffman, Absorption and Scattering of lighr by Sntall Parricles,

Wiley, New York, 1983, pp. 228-265,326-369.

'' G. Mie, Ann Phys. 25,37745 (1908).

D. Pine, D. Bohm, Phys. Rev. 85,328-352 (1952).

2' S. D. Stookey, G. H. Beall, J. E. Pienon, J. Appl. Phys. 49,51144123 (1978).

J. Zyss, J. Molecular Electronics, 1 , 2 5 4 (1985).

M. Antonieîti, C. Goltner, Angew. Chem Int. Ed. Engl. 36,910-928 (1997).

24 A. B. Buckman, Guided-Wave Photonics, Saunders College Publishing, Orlando,

FL, 1992, pp. 86.

Cbapter 2

Introduction

2.1.1 Muitiiayered Composite Materiils

In this chapter, we use some of the MSA pnnciples outlined in Chapter 1. We reiierate

Our objectives here. Firstly, we show how nano- and mesoscale multilayer hetero-

structures are assembled. We use silver and gold nanoparticles, organic spacen and

ODMASP stilbazole to compose these heterostnictures. Secondly, we illustrate how

silver nanoparticles can be selectively chemisorbed ont0 gold nanoparticle surfaces.

Thirdiy, we demonstrate how i21f, is enhanced from ODMASP on silver nanoparticles

using OCB substrates. 8

In this section, we diagram the multilayend construction of each composite. Figure 2.1

outlines the development of the MPTMS-silver-rnethyl-BDMT-goid heterostructure. We

show the reaction sequence in each stage. Figure 2.1 a shows the initial grafting of

MPThlS on the substrate surface. Figure 2.1 b shows the chernisorption of silver

nanoparticles onto the MPTMS tenninal sulfhydryl groups, followed by rnethylation (see

Figure 2. lc). Methylation covers unreacted terminai sulfhydryl. Figure 2. Id shows the

chemisorption of the BDMT spacer ont0 silver followed by gold nanoparticles in Figure

2. le. Finally, Figure 2.lf shows the complete heterostructure. We use XPS. TEM and

W-VIS spectroscopy to characterize the composite heterosuuctures on silicon wafer,

silicon monoxide TEM grids and silica glas slides.

Figure 2.2 outlines the development of the MPTMS-silver-MAA-ODMASP hetero-

structure. Again, Figure 2.2a shows the grafting of MPTMS. Next. Figure 2.2b shows the

chemisorption of silver nanoparticles, foilowed by the chemisorption of the MAA spacer

ont0 silver (see Figure 2.2~). Figure 2.2d shows ionic chemisorption of ODMASP onto

MAA by acid-base reaction. Finaily, Figure 2.2e shows the complete heterostnicture.

We use UV-VIS spectroscopy and SHG to characterize the composite on silica glas and

FO-glas slides.

To constnict these composite heterostruchires, we initially "acid-etch" the substrate by

oxidation and hydrolysis of surface silica to give silanol at the air-silica interface.' Then

we derivatize the substrate by grafting an hdPTMS subsenictural layer. We graft MPTMS

onto the substrate surface by alcohol condensation reactions. These reactions involve

MPTMS methoxy groups reacting with silanol groups to form siloxane bridges (Si-O-Si)

and methanol by nucleophilic silanol addition ont0 MPTMS silicon. Hydrolysis involves

adventitious water on the substrate surface replacing the MPTMS methoxy groups with

hydroxyl groups and forming water. We exploit the property of interfacial surface

adhesion with MPTMS. Thus, an MPTMS grafi layer forms a substnicture in which we

may introduce other subsequent adlayen on top to fabricate the complete multilayered

heterostructure.

Glassware was cleaned in alcoholic sodium hydroxide (ethanol (95 % IV)-water-sodium

hydroxide, 10: 1 : 1 v/v/w) for 12 houn and then rinsed with hydrochloric acid soiution

(10 % IV). Cleaned glassware was then rinsed with distilled ~ i l l i ~ o r e @ water and dried in

an oven at 150" C for 30 minutes. Hydrosols were prepared in distilled water obtained

from the Milli-Q-Ultrapure ~ i l l i ~ o r e ~ ~ a t e r S ystem (22 ~ i l l i ~ a k @ filter).

Metal Colioid - Hydrosol Formation

2.2.1 Süver CoiIoid Hydrosol

Materiais

Silver nitrate (99.98 95) was acquired from Engelhard Industries of Canada Sodium

borohydride (98 8) was obtained from Aldrich Chernical.

Methoci

Silver colloid hydrosols wen prepared using the method of Creighton et al.' An ice bath

was prepared to hold a 500 mL Erlenmeyer reaction flask. ~ i l l i ~ o r e ~ water (1 L) was

collected in a IL Erlenmeyer flask. In a separate 50 mL stoppered Erlenmeyer flask,

silver nitrate (3.93 x 10 -~ mrnol, 6.66 mg) was weighed (with minimum exposure to

light). Sodium borohydnde (9.3 1 x lu2 rnrnol, 3 S O mg) was weighed in another 50 rnL

Erlenmeyer flask and transferred to the 500 mL, Erlenmeyer reaction flask with distilled

water (75 mL). The silver nitrate was dissolved in water (1 8 mL) and refrigerated for 15-

20 minutes. Afterwards, the 500 rnL Erlenmeyer reaction flask (containing the sodium

borohydride solution) was stirred. Silver nitrate solution (9 mL) was added into the

reaction flask at a rate of 1 drop per second using a 10 rnL pipette. Stimng was continued

for 45 minutes until a deep golden-yellow colored solution was fonned. The hydrosol

was covered and stored in the nfrigerator.

2.2.2 Gold Coiloid EiydtosoI

Materials

Hydrogen tetrachloroaurate hydrate (99.999 95) was obtained from Aldrich Chemical.

Sodium citrate (99.0 9) was acquired from A&C American Chernicais.

Method

Gold colloid hydrosols were prepared by an adaptation of the rnethod of Weia et al,) In a

250 mL Erlenmeyer flask, hydrogen temhloroaurate hydrate (0.100 m o l , 3.41 x

1 0-2 g) was measured and dissolved in water (100 m. ) . Sodium citrate ( 1 J O m o l ,

0.50 g) was dissolved in water (100 mL). In another 250 mL Erlenmeyer reaction flask

hydrogen tetrachloroaurate hydrate solution (5 mL) was added to water (90 mL). The

solution was heated to 90" C for 15 minutes with continuous stimng. Sodium citrate

solution (5 rnL. 0.5% w/w) was immediaiely added at a rate of 1 drop per second using a

5 mL pipette. Heating was continued at 90' C for 30 minutes. The resulting deep rosé-

pink colored hydrosol solution was gradually cooled in an ice bath, covered and stored in

the refrigerator.

Muitiiayered Composite - Heterostructure Fabrication

Multilayered composites were fabricated using the method of Andrews et d4 Al1 reactor

vessel glassware (Figure 2.3) was soaked in an alcoholic sodium hydroxide solution

(ethanol(95 % /v)-water-sodium hydroxide, 10: 1 : 1 v/v/w) for 12 hours and rinsed in

hydrochionc acid solution (10 96 vlv). Afterwards, the glassware was rinsed with distilled

~ i l l i ~ o r e @ water and dried in an oven at 150' C for 30 minutes. A Schlenk line apparatus

was used to perform d1 experiments involving the reactor vessel under a nitrogen

atmosphere.

MPTMS was initially grafted ont0 silicon wafer, silicon monoxide grids and silica glass

slides. MPTMS terminal sulthydryl groups were exposed on the surface.

Substrates

Silica glass slides (23 x 10 x 0.7 mm) and silicon wafen (<LOO> crystal plane) were

obtained from VWR Scientific Instruments and Si-Tcch Limited, respective1 y.

Transmission electron microscope (TEM) copper grids (300 mesh - surface-treated with

silicon monoxide to form coated silica) were received from Soquelec Limited. The TEM

grids are referred to as silicon monoxide grids.

Materiais

Sulfunc acid (36.5-38.0 46 IV) was purchased from J. T. Baker and hydrogen peroxide

(30 % IV) was obtained fiom BDH. 3-mercaptopropyltrimethoxysilane (MPTMS) was

acquired from United Chemicai Technologies and used without further purification.

Acetone (99.8 %), chloroform (99.5 1). toluene (99.8 %) and hexane (98.5 %) were

purchased from Caledon Laboratories. Toluene and hexane were further distilled fiom

calcium hydride and dried over sodium under a nitrogen atmosphere.

rerictcir vesse1 with silica glass slides in P T E support rack

Glass reactor vessel labels

1 A - silica glass slides

1 B - PTFE support rack

1 C - reactor vessel (bonom)

1 D - silicone rubber O-ring

1 E - reactor vesse1 (top)

F - side opening

G - PTFE key valve (side opening)

H - top opening (with silicon rubber O-ring) to condenser and Schlenk linc

Method

(a) Substrate Cleaasing

Silica glas slides were inserted vertically in a poly(tetrafiuoroethylene) (PTFE) support

rack (B). Aitematively, silicon <100> crystal plane wafer fragments (23 x 10 mm) cut

from full silicon wafers with a diarnond-tipped pen were inserted venically into the

support rack. Silicon monoxide grids were held in PTFE capsules and then placed into

the support rack.

The PTFE support rack was then placed into a glass reactor vessel (C) (Figure 2.3). A

pironha solution was prepared using concentrated sulfkic acid (H2SO4) and hydrogen

peroxide (H202) (1 : 1 V/V) and was added (50 mL) carefully into the glas reactor vessel

and heated for 1-2 hours (silicon monoxide grids required only 5 minutes of heating).

NOTE: Extreme caution is required (face shield and gloves). Afterwards, the solution

was carefully poured out while manipulating the support rack with PTFE tweezers. The

substrates were immersed in ~ i l l i ~ o r e ' water and the PTFE support rack was spun for 5

minutes to rinse the substrates. After rinsing, the water was then carefully poured out

while supporting the support rack with tweezers. The rinse procedure was repeated 3

times with ~il l i~ore@ water. Aftewards, acetone was adàed to the reactor vessel and the

support rack containing the samples was spun for an additional 5 minutes. Silicon

monoxide grids were f'urther rinsed wiih chloroform. The acetone was decanted while

retaining the rack with tweezers. Acetone was evaporated by spinning the support rack in

the reactor vessel under an air atmosphere for 10 minutes.

(b) Substrate Derivatization with MPTMS

The reactor vessel was equipped with a water condenser placed into the top opening (H)

of the reactor vessel as in Figure 2.3. The condenser was attached to a Schlenk vacuum

line apparatus. The vessel was clamped and sealed by a silicone rubber O-ring (D) so that

reactor vessel bottom (C) and top (E) were secured and air-tight. Then the vessel was

dned by vacuum and mild heat (with a heat gun) and filled with a nitrogen aimosphere.

Toluene (50 mL) was syringed under a nitrogen flow through the valve (G) into the

reactor vessel containing the silicon wafer, silicon monoxide gids or silica glass slides.

The syringe was inserted through a septum into the side opening (F) of the reactor vessel

(see Figure 2.3). MPTMS (1 mL) was syringed into the reactor vessel through the side

opening (F) as well (NOTE: Ptior to use, MPTMS was transferred into a dry 50 mL side-

amed flask and stored under nitrogen). After addition of MPTMS, the MPTMS-toluene

solution was heated to 40-50' C and the support rack was spun continuously for 20-24

houn under a nitrogen atmosphere. The MPTMS-toluene solution was then aliowed to

cool. The condenser was removed from the top opening (H) of the reactor vessel (while

under a nitrogen flow). A septum was installed to seal the opening. MPTMS-toluene was

cannulated out through the top opening (H) under a nitrogen flow. The substrates were

rinsed 3 times with toluene by syringe (to add toluene) and cannula (to remove toluene).

After the final rinse, the substrates were dried under vacuum and stored in the reactor

vessel under nitrogen.

Modifications of this procedure were required for silicon wafers and silicon monoxide

grids. Silicon wafers containing the MPTMS-toluene solution were heated for 12 houn

instead of 20-24 hours. Silicon monoxide gids were plred into PTFE capsules

(uncapped) and onented verticaily in the nactor vessel (C) on top of the support rack (B).

Hexane (25 rnL) was added instead of toluene. MPTMS (0.5 mL) was added and the

MPTMS-hexane solution was heated to 30-35" C for 12-16 hours.

2.24 Silver Nanoparticies

Silver nanoparticles were chernisorbed ont0 MPTMS terminal sulfhydryl groups.

Method

The silica glas slides in the PTFE support rack were deposited into silver hydrosol in

another nactor vessel containing silver coiloid hydrosol and soaked (without stirring) for

12 hours at room temperatun. The color of the solution changed h.om golden-yellow to

aubunisrange. Substrates were removed and then rinsed once with ~i l l i~ore@ water

from a Pasteur pipette. The support rack containing the substrates was stored under

nitrogen. The silicon wafers were treated in the same way as the silica glas slides. The

solution changed in color from golden-yeiiow to charcoal-gray. The silicon monoxide

grids were treated in the following way. The g d s were placed into individual PTFE

capsules (capped) containing silver colloid hydrosol instead of being placed into the

reactor vessel. The solution changed color from golden-yellow to auburn-orange. After

thorough rinsing with ~ i l l i ~ o r e " water, the grids were placed into the capsules

(uncapped) and seaied again in the reactor vesse1 under a nitrogen atmosphere as

previously descnbed.

2.2.5 Methylation of MITMS

Where required, MPTMS substrate grafts were methylated by reaction with

dimethy lsulfate.

Materiais

Toluene (99.8 %) and uiethylamine (99 + 9%) were obtained from Alcirich Chernical.

Toluene was further distilled from calcium hydride and cûied over sodium under a

nitrogen acmosphere. Dimethylsulfate (99.7 %) was obtained fiom Eastman Kodak.

Methoà

Warm toluene (35-40' C) was syringed through a septum into the reactor vessel top

opening (H) under a nitrogen flow. Dimethylsulfate (1 mL) and triethylamine (1 mL)

were also syinged. The PTFE support rack was spun in the resulting solution for 15

minutes at room tempemure. The toluenedimethylsuIfate-triethyIamine solution was

then cannulated out through a septum covering opening (H) of F i p 2.3 under a

nitrogen flow. Wafers nacted in this way were exposed to air and washed with

~ i l l i p r e @ water, followed by methanol.

2*2*6 MAA and BDMT Organic Spacers

MAA and BDMT organic spacers were chemisorbed ont0 silver nanoparticles. Spacers

were used to bridge silver to ODMASP (with MAA) and silver to gold (with BDMT).

Materials

MAA (97 %) and BDMT (98 %) were acquired from Aldrich Chernical and used as

received. Absolute ethanol(100 46 /v) and hexane (98.5 %) were purchased from

Commercial Alcohols and Caledon Laboratories, respectively. Hexane was distilled from

calcium hydnde and dried over sodium under a nitrogen atmosphere.

(a) Silver Nanoparticle Derivatization with MAA Spacer

Siiica Glass Slides

Glass slides were inserted vertically in the PTFE support rack and placed into the reactor

vessel. Absolute ethanol(50 rnL) was syringed through a septum into the top opening

(H). MAA (2.0 rnL) was added in the sarne way. The reactor vessel containing the MAA-

ethanol solution was then heated in an oil bath (30-35' C) for 12 hours under a nitrogen

atmosphere. The support rack was spun continuously to ensure proper rnixing.

Aftenuards, the MAA-ethano1 solution was cannulated out through a septum covering

opening (H) of the reactor vessel. Ethanol was then injected to rinse the slides. The rinse

was cannulated out of the vesse1 under a nitrogen flow. This process was repeated 3

times. The slides were dried under vacuum and stored in the reactor vessel under a

nitrogen atrnosphere.

(b) Siiver Nanoparticle Derivatization with BDMT Spacer

(i) Suicon Wafers

Wafers were inserted vertically in the PTFE support rack and placed into the reactor

vessel. Hexane (50 mL) was syringed through a septum into the top opening (H) of the

reactor vessel under a nitmgen flow. BDMT (5.87 x IO-' mol, 10 mg) was carehilly

added through the top opening (H) as well. The reactor vessel was heated to 30-35' C in

an oil bath for 12 hours. The support rack was spun continuously to ensure proper

stirring. The BDMT-hexane solution was cannulated under a nitrogen flow. Hexane was

then injected to rinse the wafers. The rime was cannulated out of the vessel under

nitrogen. This process was repeated 3 times. The wafers were dried under vacuum and

stored in the reactor vessel under a nitrogen atmosphere.

(ü) Süicon Moaoxide G tids

Grids were deposited into the PTFE capsules (uncapped). The capsules were inserted

vertically in the PTFE support rack (B) and placed into the reactor vessel (C). Hexane (25

mL) was syringed into the reactor vessel through a septum into the top opening (H).

BDMT (5.87 x lo-' mol, 10 mg) was added in the same way. The PTFE support rack was

spun for 12 hours at room temperature. Aftewards, the BMDT-hexane solution was

cannulated out of the vessel under a nitrogen flow. Hexane was injected to rinse the grids.

The inse was cannulated out of the vessel under nitrogen. This process was repeated 3

times. The grids were dried under vacuum and stored in the reactor vessel under a

nitrogen atmosphere.

2.2.7 Gold Nanoparticles

Gold nanoparticles were chemisorbed ont0 BDMT terminal sulfhydryl groups.

Method

Gold colloid hydrosol was added in the sarne way as silver (sce Section 2.2.4). Silica

glas slides, silicon wafers and silicon monoxide grids were placed into gold hydrosol for

12 hours. The color of the solution remained ros6-pink. The substrates were rinsed with

~ i l l i ~ o r e @ water, followed by methanol. Substrates were placed in the reactor vessel and

stored under a nitrogen atmosphere.

A control sarnple was made by adding BDMT to silica wafer under the same conditions

as the addition of BDMT spacer onto silver nanoparticles (see Section 2.2.6). The wafer

was rinsed with hexane to nmove any physisorbed BDMT. Gold colloid was added in

the sarne way as discussed previously, followed by a distilIed ~illipore@ water rinse.

2.2.8 ODMASP Orgsaic Dye

ODMASP was chemisorbed ont0 MAA by acid-base reaction.

Materiais

ODMASP was obtained from Professor G. D. Darling, McGill University. Montréal, PQ,

and used without further purification. Methanol(99.9 9%) and toluene (99.8 %) were

acquired from Caiedon Laboratories. Poly(styrene) (MW 45000) was purchased from

Aldrich Chernical.

Method

(a) Dip-coaüng

ODMASP (0.3 - 0.9 % fw) was dissolved in a methanol-toluene solution (50 ml.

1 :9 V/V) accordhg to the method of Darling et al? The silica glass slides in the PTFE

support rack were exposed to ODMASP-methanol-toluene solution for 12- 16 hours. Al1

the sarnples were rinsed with the methanol-toluene solution and then dned under a

nitrogen Row.

(b) Sph-coating

ODMASP (0.3 - 0.9 % Iw) was dissolved in methanol-toiuene (1 :9 v/v). filtering of the

solution was done through a 0.2 mm ~ c r o d i s c ~ CR PTFE filter (Gelman Sciences). A

Pasteur pipette was used to add ODMASP-methanol-toluene solution to cover each slide.

The solution was spin-coated ont0 the slides using a photo-resist spin-coater (Headway

Research) at 1500 and 2000 rpm for 30 seconds. Sampies were rinsed with the methanol-

toluene solution and dried in air.

L2.9 ODMASP in Poly(styrene)

Substrates

iTO-glas slides (25 x 37.5 x 1 mm - la0 Nsquare surface resistivity - coated on one

side) were obtained from Delta Technologies, Ltd. Slides were taped on the coated side to

allow for an exposed electncal contact ana to apply a voltage for corona discharge

poling.

Materials

ODMASP was acquired from Professor G. D. Darling, McGill University, Montréal, PQ

and used without further purification. Polystynne (MW 45000) was obtained from

Aldrich Chernical. Methanol (99.9 %) and toluene (99.8 %) were obtained from Caledon

Laboratories and used without further purification.

Method

Poly(styrene) (PS) (2.68 x IO-' mol, 1.2 10 g) was measured into a 5 Dram glas via1 and

dissolved into a methanol-toluene solution (1:4 v/v). ODMASP (1 .O mol 96) was

dissolved into the PS-methanol-toluene solution and stimd with a magnetic stir bar.

Continuous stirring was maintained for 1 hour. The solution was filtered through a 0.2

mm ~crodisc~ CR PTFE filter (Gelman Sciences) into another 5 Dram glas vial. The

solution was dipensed onto an KO-glas slide (onto the ITO-coated side) using a Pasteur

pipette and spin-coated at 1500 and 2000 rpm for 30 seconds using a photo-resist spin-

coater (Headway Research) to produce films of thickness 1-3 p.

XP spectra were recorded using an ESCALAB 220i-XL (Fisons Instruments) spectro-

meter (Al K, radiation source). Each sarnple area (1 x 1 mm) was exposed to a 10 keV

electron source at 200 W power and 5 x lo0l3 atm (4 x 1 0 ~ ' ~ Torr) intemal chamber

pressure. Binding energies were refennced to the Au fin line at 84.0 eV. Data were

convertcd with ~c f i~ se@ V 1 . 7 ~ and d y z e d using or pro@ V2.01 software. Data were

acquired at the Institut National de la Recherche Scientifique-Université du Québec à

Montréal (Énergie et Matdriaux, INRS-UQAM), Varennes, PQ. TEM analyses were

performed using the Je01 JEM-2000FX and the Philips 400 EM electron microscopes at

33000 X magnification. Micrographs were developed using 2.5 X and 5 X magnification

from the negatives. Particle size diameten were measured using Sigma ~can@ Pro 4

software. UV-VIS measurements were taken using an HP8452 UV-Visible spectrophoto-

meter (mercury larnp) with a reference silica glas slide (0.7 mm thickness). Film

thicknesses for 2'' were measured using a Dektak (Sloan Technology) profilorneter from

the Photonics Research Group, École Polytechnique de Montréal, Montréal, PQ.

SHG measurements for analyzing the i2' nonlinear optical susceptibility were perfomed

using a Q-switched Quanta-Ray DCR neodyrnium-doped yttrium-aluminum gamet

(Nd:YAG) laser (output A = 1064 nm) with a 10 ns pulse width at 5 ml and a 10 Hz

repetition rate (set Figure 2.4). Sample and x-cut quartz crystal reference mounts (Oriel

Instruments) with rotation speeds of 2' per minute €rom O - 60' were used, in addition to

photomultiplier tubes (PMTs) (Hamatsu Company) and dual-channel boxcar integrators

(Stanford Company). The SHG signai was recorded from -50' to +50° for the quartz

reference and from O - 60" for the sample, and then amplified and averaged using the

boxcar integrators. In Figure 2.4, a minor kaction of the incident laser light transmits

through the 2 0 zcut quartz crystal reference to produce SHG. The PMT detects the SHG

signai and uses the signal as a reference channel for removing laser fluctuations in the

SHG signal from the sample. The major fraction of the incident laser light enters the

sample surface to produce the SHG signal. The fundamental harmonic bearn from the

laser passes through a polarizer and a half-wave plate to p-polmize (O0 with respect to the

plane of incidence) the fundamental harmonic. A cut-off fdter placed in front of the beam

path of the laser then filters the fundamental harmonic. The laser enters the sample and

the SHG signal from the sample suface results. The fundamental light reflected from the

surface propagates dong with the SHG to a thin 2-cut quartz crystal, frorn which more

SHG signai is produced. The phase relationship between these 2 sources of SHG is

detennined by the position of the z-cut quartz dong the beam path. By translating the z-

cut quartz paralle1 to the beam path while monitoring the SHG, an interference pattem

results, which describes the relative phase between the fundamental hannonic incident on

the sample surface and the SHG produced at the surface. The phase difference can be

extracteci €rom the interference pattern (Maker fnnges) by replacing the sample with

another zcut quartz of known orientation and then repeating the interference expriment.

Aftenvards. the SHG light enters through another polarizer set to p-polarize the second

harmonie. A filter separates the second harmonic fiom the fundamental harmonic signal.

The SHG signal enten a PMT and boxcar integrator monitors the output. Maximum i2' was determined using Microcalc Clrigin@ 3.73 software. Al1 measurements were

performed in the Materids Research Center and the Department of Physics and

Astronomy, Northwestem University, Evanston. IL.

Q-switched Nd:YAG laser ( A = 1064 nm) lem

boxcar integrator

and cornputer

I v

polarizer * . -

PMT monochromator quartz reference

4 * u

Pm

Figure 2.4: Second hamonic generation (SHG) apparatus for measuring i2'

Resuits and Discussion

2.3.1 X-ray Photoelectron Spectroscopy (XPS)

In this section, we locus on the microstructural analyses of the multilayered composites.

We use XPS to follow the layer-by-layer construction of the multilayered MPTMS-

silver-methyl-BDMT-gold heterostmcture. A flowsheet ouilines how the sarnples were

fabricated and characterized (see Figure 2.5). A control sample was used to determine

whether or not BDMT andor gold were deposited ont0 silicon. Figure 2.5, Tables 2.1 and

2.2 summarize the results.

Table 2.1

MPTMS-silver-methyl-BDMT-gold heterostmcture on silicon wafer

Samp ies Layers

Con trol

Sample A

Sarnple B

Sample C

Sample D

Sample E

Sample F

Sample G

Sample H

BDMT + gold

MPTMS (exposed to air)

MPTMS (unexposed to air)

MPTMS-methyl

MPTMS-meth yl-silver

MPTMS -s il ver

MPTMS-silver-meth yl-gold

MPTMS-silver-methyl-BDMT

MPTMS-silver-meth y 1-BDMT-gold

Figure 2.5

Flowsheet - MPTMS-silver-methyl-BDMT-gold heterosenicture on silicon wafer and silicon rnonoxide grids

Sarnple A s Silicon <IO> Wafers

Silicon Monoxide TEM Gnds

(exclusion of air)

Graft MPTMS

r

Addition of

Colloidd Silver

Sample F 9 Sample G 9

Addition of

Colloidal Silver

Addition 1 1

Colloidal Gofd

1 Addition 1

Addition El Addition

Colloidal m-

Addition

(exclusion of air)

Table 2.2

Elemental binding energy6 MPTMS-silver-methyl-BDMT-gold heterosenicture

on silicon wafer

Element Theoretical Sample Sample Sample Sample Sample Sample Sample Sample Values A B C D E F G H (eV) (eV) (eV1 (eV) (eV) (eV) (eV) (eV) (eV)

Appendix Figures A-1 to A-4 (inclusive) contain the XP spectra. Repnsentative features

indicate silicon, carbon, oxygen, sulfur, silver and goid. Sulfur 2pln and 2pm Iines

monitor sulfur-silver, sulfur-carbon and sulfur-gold interactions. Spectra were not

deconvoluted, thus binding energies are derived from peak maxima of spectra.

Control Experiments

These initial experiments eliminate the possibility of defects within the layers. We use the

following control samples to venfy that we were fabricating the correct multilayered

heterostmcture. Figures A- l(contro1) and A-2(control) show the XP spectra for these

samples. As described in the Section 2.2.7, silicon wafer fragments wen immersed in

BDMT-hexane solution, rinsed and scanned for the presence of sulfur by XPS. No

evidence of physi- or chemisorbed BDMT was found. Similady, silicon wafer fragments

that were exposed to gold hydrosol showed no evidence of physi- or chemisorbed gold.

From these results, we were able to continue with the layer-by-layer construction of the

heterostnicture.

Samples A and B: MPTMS (exposed and unexposed to air)

These experiments show the result of exposing the MPTMS graft to air. We wanted to

see if oxidation of MPTMS terminal sulfhydryl functional groups was a factor. We

prepared two samples - Sarnple A and Sarnple B. Sample A was exposed to air (see

Figures A- l a and A-2a and Sample B was not exposed. Sulfur S 2pin and S 2~~~ bands

(sulfur S 2p doublet band) illustrate that Samples A and B differ somewhat. Sarnple A

(exposed to air) shows an unresolved sulfur S 2p doublet band. while Sarnple B

(unexposed to air) shows a mon resolved sulfur S 2p doublet band. Sarnple B shows the

sulfur S 2p doublet band approaching a 1:2 ratio7 for S 2pinand S 2mn. The difference in

oxidized versus unoxidized sulfur may affect the multilayer uniformity. We explain this

difference in the following. In Sample A, less MPTMS terminal sulfhydryl groups are

available for silver nanoparticles to chemisorb onto since some sulfhdryl groups may

already be oxidized. Consequentiy, these oxidized sulfhydryl groups are not able to react

and chemisorb ont0 silver nanoparticles.

Sample C: MPTMS-mcthyl

These next experiments show the methylation of M P T M S terminal suifhydryl groups. We

wanted to sec if MPTMS cm k methylated. If so, we wanted to see the extent of

methylation. These experïments will be important in loter experiments when gold is

chemisorbed oato the silver surface. Figures A-lc and A-2c show spectra for methylated

MPMS. Methylation reduces the intensity of the sulfur S 2p doublet band of free

sulfhydryl (see Figure A-2c). A shifk to an increased oxidation state of the sulfur S 2p

doublet band results from a different chernical environment. We attribute the S 2p band

shift to rnethylation, but we still see the original S 2p band of umeacted terminal

sulfhydryl groups at 165.8 and 164.9 eV. Therefore, not dl the MPTMS sulfhydryl

groups have ken methylated. Other overlapping contributions from incomplete

rnethylation may be due to hydrogen bonding of H from sulfhydryl to dimethylsulfate to

form RS-H-O. Leavell et al.' detemined the extent of hydrogen bonding from sirnilar

chernical shifts. Therefore, we attribute these overlapping bands to hydrogen bonding

interactions.

SampIe D: MPTMS-methyl + siiver

Now that methylation of MPTMS was demonstrated, these next experiments show the

extent of methylation after exposure to silver nanoparticles. MPTMS sulfhydryl groups

are initially methylated and then silver nanoparticles are added. Figures A- ld and A-2d

show spectra for methylated MPTMS, followed by exposure to colloidal silver. We

conclude that not al1 the MPTMS sulfhydryl groups are methylated since the sulfhydryl

sulhr S 2p doublet band remains. Therefore, silver nanoparticles chemisorb ont0 the

remaining exposed MPTMS terminal sulfhydryl groups. We observe the presence of both

methylated and chemisorbed silver in Figure A-2d.

Sample E: MPTMS-silver

These expenments show the chemisorption of silver nanoparticles on M P I U S . Figures

A-le and A-2e show specva of MPTMS after exposure to colloidal silver. The sulfur

S 2p doublet band is unresolved (as in Sample A). Figure A-3e shows silver Ag 3d3R and

Ag 3dsn bands. These bands are more intense than those in Sample D, therefore,

indicating the chemisorption of more silver.

Sample F: MPTMS-dver-wthyl-gold

These experiments show that gold nanoparticles do not chemisorb onto the substrate,

methylated MPTMS, or to silver nanoparticles that have not k e n derivatized with

BDMT spacers. Figures A-If, A-2f and A-4f show spectra of MPTMS afkr exposure to

colloidal silver, methylation, and then colloidai gold. Gold does not chemisorb ont0

M P T M S sulfhydryl since methyl covers the available sulfur. Sulfur S 2p doublet bands

confirm complete methylation (see Fipn A-2f). Samples C and D are very sirnilar to

Sample F since methylation occurs in dl.

Sample G : MPTMS-silver-meth y 1-BDMT

These experiments show the chemisorption of the BDMT spaccr on silver nanoparticles.

Figures A- lg and A-2g show spectra for MPTMS after exposure to colloidal silver,

methylation and BDMT. Figure Adg shows sulfur S 2p doublet bands from exposed

BDMT terminal sulfhydryl. The MPTMS terminal sulfhydryl spectnim appears tc be

screened b y the silver nanoparticle and meth yl adlayea. Therefore, we do not see

MPTMS sulthydryl. Sample A and B are similar to Sample G since free exposed terminal

sulfhydryl is observed. Thenfore, BDMT chemisorbs successfully since BDMT contains

exposed sulfhydryl.

Sample H: Mm-silver-metbyCBDIMT-gold

These experiments show the chemisorption of gold nanoparticles ont0 BDMT. Figures

A- lh, A-2h. A-3h and A-4h show spectra for MPTMS after exposure to colloidal silver,

methylation, BDMT and colloidal gold. Gold covers BDMT well as indicated by the

reduction in intensity for the BDMT sulfhydryl compared to Sample G. A broadened line

at 174-166 eV may indicate varied oxidations States of the sulfur-gold interaction. The

gold Au 4fin band shifts indicating, perhaps, an incnase in oxidation state. Therefore,

this shift may provide additional confirmation that gold chernisorbs onto BDMT

sulfhydryl. h addition, the chemisorption of gold and BDMT dramatically damps and

reduces silver Ag 3du2 and Ag 3dsn band intensities (see Figure A-4h). Wagner and

~ i l o e n ~ amibuted damping effects to the metdlic scnening from gold.

Now, we have the complete MPTMS-silver-methyl-BDMT-gold heterosmicture. We

have clearly show that we can monitor the layer-by-layer sequence of the multilayered

composite using XPS. We now use transmission electron microscopy (TEM) to analyze

the surface in the next section.

In this section, we use TEM to probe the MPTMS-silver-methyl-BDMT-gold multilayer

and image the surface topography in detail. Figure 2.5 shows a flowsheet outlining the

fabrication of the multilayered composites on silicon monoxide treated copper TEM

grids. We investigate the MPTMS-silver-methyl-BDMT-gold heterostmcture (Sample H)

(see Table 2.1). Sample H shows grafted MPTMS, followed by exposure to colloidal

silver, methyiation of MPTMS sulfhydryl groups, and exposure to BDMT and colloidal

gold.

The purpose of these experiments was to see the METMS-silver-methyl-BDMT-gold

construction (see Figures 2.6a and 2.6b). We see a random distribution of both silver

(light-colored particles) and gold (darkcolored particles) nanoparticles. Silver particles

do not ovedap since they are bound to the surface by MPTMS only. These silver

nanoparticles are polydisperse with 4.50-9.00 nm diametea and possess average

diameters of eu. 6.57 f 1 .O2 nm. Figure 2.7a shows a histogram of the silver nanoparticle

size distribution. In Figure 2.6b, we see that the gold particles (larger dark-colored

particles) chernisorb exclusively ont0 BDMT and not onto other gold particles or the

silicon monoxide grid surface. Controls confirm that gold particles do not chernisorb

directly ont0 silver particles (smaller light-colored particles) without the BDMT spacer or

the silicon monoxide grid. Gold coverage is less than that of silver and may be due to low

coverage of BDMT spacer or diffennt adsorption kinetics for gold on BDMT versus

MPTMS. Solvent and temperature effects may influence the adsorption thermodynamics

since low reaction temperatures (30-35T) were used. Silver oxides may prevent

chernisorption of BDMT as well. Gold nanoparticles are polydisperse and confirrn the

observations by orem mus.'^ These polydisperse gold particles have 9.75- 16-75 nm

diameters and possess an average particle diameter of ca. 12.59 I 0.75 nm. Figure 2%

shows a nanoparticle size distribution that agrees with observations of Turkevich et al.

We observe that gold nanoparticle coverage is similar to that of silver (see Figure 2.6a).

The larger gold particles appear to cover silver only. We see variations in density of

nanoparticle distributions in certain regions in Figures 2.6a and 2.6b. These density

variations are due to the gold particle diameters being larger than silver. Not al1 the silver

particles are covered by gold. therefore, the particle density appears lower. If we assume

that at least one gold particle covers one silver particle, then the total area of particle

coverage would increase. As a result, mon of the grid surface would be occupied.

if we observe closely in Figure 2.6b, we notice interesting phenomena in the nanoparticle

distribution (see Figures 2.7a and 2%). In region A, we see separate silver particles

(smaller light-colored particles). Some gold particles (larger dark-colored particles) are

seen chemisorbed ont0 the silver. In region B. we see ciendritic formations of silver

particles. These formations are indicative of fractal behavior and we will explore this

detail in the next section. In ngion C, we see separate silver particles only. No separate

gold particles are observed. This observation clearly confirms that gold chemisorbs ont0

BDMT (which is chernisorbed ont0 silver). Gold does not chemisorb onto the silicon

monoxide grid itself since we do no< see separately scanered gold particles. Al1 gold

particles are added onto silver. We thus confm that gold does not chemisorb onto

MPTMS terminal sulfhydryl due to methylation. In ngion D, we notice dark linear bands

on several silver particles. These bands may imply silver particles eclipsed or twinned by

gold.'2 In region E, we observe aggregated gold particles. Several particles appear to be

hexagonally aggregated. We amibute this aggregation to hexagonal close packing of

silver. This packing distribution may be nlated to a parameter that quantifies how

distribution affects the propagation of light. We denote this parameter of dimension, d. h

hexagonally close packed silver, the dimension is trivial (d = 2). From the rnicrograph,

we observe an apparent random packing distribution, therefore, we assume that another

non-trivial dimension does exist. We will now explore this other dimension next.

Figure 2.7a: Histogram - silver nanoparticle size distribution

Figure 2.7b: Histogram - gold nanoparticle size distribution

Fractai Dimension

In Figure 2.6% we see a nanoparticle distribution showing apparent dilation symrnetry.

The distribution appears to be the same when viewed on a dilated scale. Such a

distribution is a fraftal. Using the method developed by Weitz et al? we exarnined the

MPTMS-silver-methyl-BDMT-gold sample for a non-trivial Fracta1 dimension. Figure

2.6b shows how the fractal dimension is calculated. We assume an average particle mass

(2.0 x IO-'' g for each silver particle and 3.7 x 10-17 g for each gold partick) and then

draw concentric circles of radius, R, around a point of mass. M, and count the number of

particles within each circle (inclusively). A fracta1 structure will scale according to

where d represents the Euclidean dimension of space. No scale invariance occurs when

d = dr , where dr represents the fractal dimension and quantitatively characterizes the

long-range dilation symrnetry. A fractal dimension with scale invariance occurs when

d > dl (where df is not an integer). We count the number of silver nanoparticles in each

concentric circle and determine the Euclidean dimension (see Figure 2.6b). We follow the

sarne method for counting the number of gold nanoparticles. The larger and darker gold

nanoparticles are counted. Bias in counting may be minimized by counting nanoparticles

in different circular regions and averaging the nanoparticle numbers that have the same

circular diameter, R. Figure 2.8a shows a plot of h ( M ) versus h ( R ) for silver

nanoparticles where the slope gives d!, the fractal dimension. Similady, Figure 2.8b

shows a plot determinhg the fracta1 dimension for gold nanoparticles.

WR)

Figure 2.8a: Logarithrnic plot - silver nanoparticle fractal dimension

Figure 2.8b: Logarïthmic plot - gold nanoparticle fractal dimension

Silver nanoparticles occupy a fracta1 dimension, df, of 1.45 i 0.08. Similarly, gold

nanopanicles appear to imprint, imbed into and replicate the silver fractd topography as

well. niese gold nanoparticles occupy a fractal dimension of 1.76 f 0.13. Andrews et

al.13 discovered similar fractal dimensions of metai nanoparticles embedded into

poly(pyrro1idone) on TEM grids. The measured fractal dimension agrees with the

diffision limited aggregation (DM) model on surfaces. This model involves the

diffision and adsorption of individual nanoparticles ont0 the outer vacant edges of an

existing aggregate. More specifically. the depositiondifision-aggregation (DDA) model

may better chvacterize nanoparticle monolayer for~nation.'~ This model diffen fiom the

DLA mode1 since it involves nanoparticle deposition onto an existing monolayer

aggregate and the difision of each nanoparticle towards a vacancy in the monolayer.

We now use W-VIS spectroscopy to analyze the various rnultilayered composites fiom

the measured absorbance spectra. Tables 2.3a and 2.3b define the compositions of the

heterostmctures that were studied on silica glas slides.

Table 2.3a

MPTMS-silver-methyl-BDMT-goId heterostnicture on silica glass slide

Sarnple Layer

Control Gold (in solution)

Gold-BDMT (in solution)

F MPTMS-silver/gold

MPTMS-silver/gold-BDMT

G MPTMS-silver

MPTMS-silver-BDMT

H MPTMS-silver

MPTMS-si1 ver-me th y 1-BDMT-gold

Table 23b

MPTMS-silver-MAA-ODMASP heterostnicture on silica glas slide

Sample Layer

Control MPTMS-silver-ODMASP

A MPTMS-silver

B MIPTMS -silver-MAA

C ODMASP

D MPTMS-silver-MAA-ODMSP

Figure 2.9

Flowsheet - MPTMS-silver-MAA-ODMASP on silica glass slide

Silica Glass Slides s Addition

Colloidal

of MAA

1

Addition of

ODMASP

Addition of

ODMASP

i) MPTMS-silver-methyi-BDMT-gold hefemstnicture

We now examine the W-VIS spectra of the following samples to determine the effect of

silver and gold with the BDMT spacer in the multilayered composite heterostnicture.

Control Smple: gold + BDMT (in solution)

These experiments show the result of chemisorption of BDMT on gold in gold hydrosol.

This LW-VIS control sarnple differs From the X P S control sample in that we perform this

control expriment in solution instead of on a silicon wafer. Figure 2.10a shows gold

hydrosol before and after exposure to BDMT. When BDMT chemisorbs ont0 gold

colloid, the absorption spectnim exhibits a shoulder centered near 650 nm.

Sample F: MPTMS-süver/gold-BDMT

These expenments show the result of chemisorption of BDMT on silver and gold

nanoparticles. This UV-VIS Sample F differs from the XPS Sample F in that we adsorb

colloidal silver first. then colloidal gold and BDMT. For the XPS Sample F, we

chemisorbed silver, methylated MPTMS, chemisorbed BDMT to silver and then

chemisorbed gold. Figure 2. lob shows spectra for equimolar colloidal silver and gold on

grafted MPTMS before and afier B D W chemisorption. Large broadening of the

absorption specuum arises from silver and gold surface plasmon band overlap. The silver

plasmon absorbance maxirnizes at 461 nm and 467 nm.

Sample G: MPTMS-silver-BDMT

These experiments show the chemisorption of BDMT on silver nanoparticles. This W-

VIS Sample G is identical to the XPS Sarnple G with the exception of MPTMS

methylation. Figure 2.10~ shows spectra for colloidal silver on grafted MPTMS before

and dter exposure to BDMT. The silver plasmon blue-shifts from 452 nm to 44L nm.

The absorption spectnim undergoes broadening from 300-375 nm and therefon, indicates

silver-BDMT interaction.

Sample H: MPTMS-suver-methyl-BDhlT-gold

These experiments show the chemisorption of gold nanoparticles on BDMT chemisorbed

ont0 colloidal silver. This W-VIS Sample H is identical to the XPS SampIe H. Figure

2.10d shows spectra for colloidal silver on grafted MPTMS before and after methylation

of MPTMS, followed by exposure to BDMT and colloidal gold. The silver plasmon blue-

shifts fiom 452- nm. We observe a visible color change from golden-yellow to rosé-

pink. This observation may indicate that the silver plasmon couples with gold. Conon et

confirmed that silver and gold coupling does indeed occur by blue-shifting in the

UV-VIS spectrum.

300 400 500 600 700 800 Wavekngth (nm)

Figure 2.10a: UV-VIS spectrum - gold-BDMT in aqueous solution

Wavekngth (nm)

Figure 2.lOb: UV-VIS specmm - WS-silverlgold-methyi on silica glass slide

300 460 500 600 700 Wavelength (nm)

Figure 2.10~: UV-VIS spectmrn - MPTMS-silver-methyl-BDMT on silica g l a s slide

Wavdmgth (nm)

Figure 2.lOd: W-VIS spectrum - MPTMS-silver-methyl-BDW-gold on silica giass slide

ü) MPTMS-silver-MAA-ODMASP heterostructure

We examine the W-VIS spectra of the foiiowing sarnples to determine the effect of

silver on ODMASP. ODMASP possesses polarizable pz-electron orbitals and electron

delocaiization occurs h m pxsrbital energy o ~ e r l a ~ . ' ~ Figure 2.1 1 shows the fomal

charge transfer process fiom the donor (dkylamino group) to the acceptor (pyridinium

group) to fonn the excited state.

t Excitai Statc

Figure 2.11: ODMASP charge transfer between rr-a* States

ODMASP probably forms an amphiphilic layer on the silver surface involving the Cis

hydrophobie alkyl tails and pyridinium hydophilic head (see Figure 2.12). The ODMASP

pyridinium nitrogen (lone electron pair) interacts by acid-base reaction with a proton

fiom MAA carboxylic acid. The MAA carboxylate anion delocalizes negative charge

whe~as the pyridinium nitrogen retains and localizes the positive charge. Acid-base ionic

chemisorption of ODMASP ont0 MAA positions ODMASP close to the silver surface.

Cross et al." c o d h e d that a Ci &y1 spacer positions the NLOD close enough to the

silver surface without disruption in charge transfer.

N""C'"Hn' I Hy drop ho bic La yer

// Hyperpolarizable Layer

Silver Nanopartic le Surface

Figure 2.12: ODMASP chernisorbed onto MAA (acid-base)

We conducted the following control experiments. Initially, we attempted to chemisorb

MAA ont0 the silica glass slides by alcohol condensation reactions. We also endeavond

to chemisorb ODMASP directly ont0 the glas slides by ionic and hydrogen bonding

interactions using the methanol-toluene (1 :9 vlv) solution for ionically chemisorbing

ODMASP ont0 MAA. As well. we attempted to chemisorb ODMASP ont0 silver by van

der Waals attraction with the methanol-toluene solution. From these control expenments

we conclude that both MAA and ODMASP do not chemisorb significantly ont0 acid-

etched, unfunctionalized silica glas slides and ODMASP alone does not chemisorb

significantiy ont0 the MPT'MS-silver heterostnxcture either.

400 500 600 700 000

Wavekngth (nm)

Figure 2.13: UV-VIS spectra - MPTMS-silver-MAA-ODMASP heterostnicture

on silica glass slides

These next experiments show the layer-by-layer construction of the MPTMS-silver-

MAA-ODMASP heterostnicture. Figure 2.13 shows spectra of colloidal silver on grafted

MPTMS (Sample A), followed by exposure to MAA (Sample B), and then exposun to

ODMASP (Sample D). We see in Sample A the signature of the surface plasmon band

maximum at 415 nm as confirmed by Bohren et a1.18 Subsequent adsorption of MAA in

Sample B suppresses the plasmon absorbance. Kreibig et al. observed that silvet-sulfur

interactions alter the fne electron density and darnp the plasmon absorbance. Sample C

shows free ODMASP with a maximum absorbance wavelength (A-) at 394 nm. We see

that this absorbance corresponds to the first electronic transition (So -+SI) and overlaps

with the silver plasmon absorbance (compare Samples A and C). Therefore. plasmon

enhancernents a cu r and promote the elecmnic excitation of ODMASP. Sample D shows

ODMASP reacting with MAA to form the MPTMS-silver-MAA-ODMASP

heterostructure. Decher et al?' obsmed that ionic acid-base chemisorption was indeed

an excellent way to construct multilayereà heterosmicnires. Spectral broadening implies

agpgation of ODMASP monomers as noted for stilbazolium dye salts by Xu et af?

Initialiy, we observe that the silver plasmon band absorbance maximum red-shifts from

344 nm to 445 nm. We may offer general explanations for the spectrum features. Firstly,

we rnay invoke a chemical effect. This effect occm when the ODMASP causes changes

in the ODMASP electronic stnicture. Secondly, we may invoke an electromagnetic

effect. This effect occurs when the plasma osciliations contribute to the molecular

eigenstates. In the fint case, protonation of ODMASP by MAA modifies the

eigenenergies and eigenhinctions of the adsorbate. In methanol, protonated ODMASP

shows a strong red-shifted absorption band at 470 nm and a weak absorption band at 320

nm. If these bands exist, then image-dipole interactions between ODMASP-H+ and the

silver surface would repnsent an additional perturbation on the ODMASP eigenstates.

Therefore, the absorption energy spectnim may simply represent protonated ODMASP

on MAA superimposed on the plasmon band of silver. In the second case, however, the

resonant response of the metai nanoparticles may actually by strongly coupled to the

absorption from the ODMASP layer. Measurernents from rhodamine B on colloidal silver

adsorbed ont0 glas reveal strong coupling between the adsorbate and silver? The

plasmon absorbance at 520 nm for uncoated silver nanoparticles splits with the bands

blue- and red-shified from the 520 nm plasmon band of the uncoated nanoparticles. The

strength of coupling depends on the degree of overlap of the absorption spectra of the dye

with the silver plasmon, the particle size and shape and the coating thickness.* From

Glass et al.18 and ~ a ~ e n , ~ ~ we suggest that the band in the plasma resonance of our coated

silver nanoparticles may be associated with the opticai resonance of the conduction

electrons through the dispersion in the reai part of the ODMASP-El? dielectric function

and through the absorption of ODMASP. In the next section, we suggest how this optical

nsonance effect can indeed enhance i2)

2.3.4 Second Harmonic Generation

We proceed to measure the SHG from the i2) nonlinear optical susceptibility. These

measurements were obtained from the multilayered composite containing both MPTMS-

silver and MPTMS-silver-MAA-ODMASP betetosüuctures on RO-glass slides. We

examine the obtained maximum as outlined in the experirnentai conditions (see

Section 2.2.10). In SHG experiments involving 22' measurements, both fundamental (a)

and second hamonic (20) waves propagate in the same direction. The wave vector

difference between the waves is described by

where k = n d c and k represents the wave vector, n is the refractive index, a, is the

fundamental frequency, Zn, is the second h m n i c frequency and c is the speed of light.

Since Ak t O, harmonic field components do not propagate in phase. Effective phase

matching occun when the second harmonic coincides with the fundamental wavelength.

Nonlinear optical susceptibility for SHG was measured by the Maker fringe techniquez

as described by Jerphagnon and ~ur t z? In this technique, the plane of the sample on

ï ï0-glas is rotated through an angle from O* to 60' to produce a fiinge pattern.

Birefringence phase matching was achieved through angle tuning, which uses the angle

dependence of the refractive index of the p-polarized wave relative to the optical wis. It

is usehil to define a nomalized f ' for p-polarized excitation as

where I, is the intensity of the excitation laser pulse and 12., is the intensity of the

comsponding SHG signal. A 1064 nm wavelength was chosen to have a Za, wavelength

overlap one of the observed electronic UV-VIS spectral bands. An alternative to the

birefringence phase matching is the conversion of the second harmonic wave to Cerenkov

radiation." On the basis of resonance enhancement, the SHG signal with 2n,

at 532 nm may become enhanced by the broad electronic transition band of ODMASP at

344 nm as well as from the overlapping silver plasmon band ai 445 nm (see Figure

2.13d). Thenfore, the nonlinear response may have contributions from both bands.

From these experiments, we show the 2'' response of the MPTMS-silver-MAA-

ODMASP heterostructure in Table 2.4.

Table 2.4 suggests that the iZCZ' from ODMASP may be enhanced by silver surface

plasmon excitations by the laser optical field and therefore, cocf~nas our previous

conjecture that a coupled enhancement may indeed occur.

Table 2.4

i2' for MPTMS-silver-MAA-ODMASP, MPTMS-silver and PS-DMASP heterostnictures

He terostruc ture f ' ( IO-* C ~ I J ~ , 10-* esu)

MPTMS-silver-MAA-ODMASP 1.48,4.00

The increase in i2' of ODMASP on silver suggests the influence of increased

hyperpolarizability, number density and local fields. We discuss the effects of these

factors show in our experiments later on.

Originally, we prepared and obtained samples of ODMASP for SHG experiments. The

fint sample consisted of ODMASP doped into poly(styrene) to form a PS-ODMASP

composite. The concentration was approximately 1 mol 46 ODMASP, which arnounts to

a number density of approximately 500 ODMASP monomers per nm2 (1 pm film

thickness). Due to thermal degradation of our sample, we used (a-[4-(N&-dimethyl-

arnino)]styrylpyridine (DMASP) from Marks et al? for cornparison. A sample that was

pied by coma discharge gave a P' of 0.29 IC 110'" ~ I J ~ (0.78 x 10' esu). ODMASP

chemisorbed ont0 MAA in the MPTMS-silver-MAA-ODMASP heterostnicture gave a

2'' of 1 A8 x luU C?/J~ (4.00 x lu8 esu). Both samples were exposed to 1064 nm light

from an Nd:YAG laser for SHG. These experiments were performed to show that the

silver nanoparticle optical fieids enhance i2' of the MPTMS-silver-MAA-ODMASP

heterostructure. This enhancement is not available in the PS-DMASP composite.

Orientational Order

We must therefore explain the differences in the measured i2' values in terms of (1)

differences in sample preparation relating to orientational order and (2) possible roles for

surface plasmon enhancements. Let us fmt consider the orientational order. Differences

in ;S2' rnay possibly be due to differences in polar orientational order. Corona poling

foms a nonequilibrium distribution of oriented monomeric DMASP. These dipoles will

spontaneously relax towards a random configuration (increased configurational entropy)

unless physically impeded by the host polymer matrix. Various techniques for impeding

the relaxation process may provided by lattice hardening for anchoring NLODs. DMASP

in poly(styrene) corresponds to the unanchored lattice hardening since the polyrner is not

cross-linked, and the DMASP is not covaiently chemisorbed to the polymer. Therefore.

DMASP polar orientation correlations c m decay immediately after the corona poling

field ceases at room temperature. Since the nonlinear susceptibility was measured

immediately after corona field poling, the measured 2'' most Iikely reflects the value that

would be obtained for the highest degree of order. This i2' assumes that the corona

poling process is efficient. We rneasured the growth of XI2' in situ and then maximized

the polar orientational order.

Surface Plasmon Enhancement

Let us now consider the surface plasmon enhancements. We consider the effects at the

metal interface. Optical SHG has been produced from roughened silver surfaces2' and

colloidal silver monolayers on Langmuir-Blodgett films. Typicall y, nonlinear effects in

the silver derive ffom electrîcal field gradients and surface effects to produce SESHG.

The second harrnonic field amplitude generated from an interfacial nonlinear polarization

on the silver surface is obtained by the use of an effective tensor. In actuality, the

measured X<Z' is temed the effective i2' and derives fiom the i2jM=, x"'La;fEl, f and X"'6m tensor components as described by ~revet~' in the fonn

where i2)sJa, i 2 j S , , f l I J P and i2)s,, are the surface 2"srder nonlinear susceptibility

tenson, E is the applied field and i3'=, i3L, XI3'= and i3'= are the 3*-order nonlinear

susceptibility tensors. Since the second harmonic field amplitude is proportional to the

tensor amplitude, we can expect a nonlinear intensity for the response to be proportional

to the quaciratic of the tensor amplitude as shown in Equation [12]. We use f ' to

represent i2)@, or in essence, ~ 2 J ~ c Z Z X , i2)&- and iZ)Cfim, throughout the thesis, when

refemng to our nonlinear optical susceptibility measunments. Usually, i2 '~ , dominates but in the case of surface-enhanced SHG (SESHG) the other tensor

components must be accounted for. We will explore SESHG regarding our experirnental

samples next.

From our samples, we should see evidence of SHG as a result of surface enhancement of

colloidal silver in the MPTMS-silver heterosmcture. From our measurements, the

control sarnple of silver nanoparticles in the MITMS-silver heterostructure produced no

SHG after exposure to 1064 nm laser light. Thecefore, no direct contribution of 532 nm

light from the silver nanoparticle layer was observed using Our conditions of sarnple

preparation and measurement. We may explain this occumnce in terms of nanoparticle

distribution. Our MPTMS-silver heterosenictural samples on TEM grids showed fractal

distributions of silver nanoparticles. Fractal distributions have not yet been explorcd

extensively for SESHG. Depending on the extent of fractality, the SESHG signal may or

may not be detected. McGum et al." concluded chat multiple scattering by disordered

distributions such as fractals may decrease SESHG. As we explore further, the details for

this occurrence will become clear.

We see that SESHG in silver occm as laser light impinges on the surface. We may

describe the subsequent SESHG prwess by the following. ûn the süver surface, we may

use describe a free electron gas at the silver-air interfa~e?~ We assume that the electron

density is a hinction of oscillations at both the fundamental and second harmonies of the

incident electromagnetic wave. These harmonic oscillations superimpose upon each other

and occur at certain incident angles. Some of these angles correspond to surface silver

plasmon modes of the impinging laser. Unfortunately, fractd distributions rnay not

support these oscillations at al1 incident angles. For silicon monoxide TEM grids, a

fractai distribution was confirmed. We infer that these nanoparticle fractal distributions

rnay be similar for the ITO-glass samples that were measured for 22' during SHG

éxperirnents. We deduce that the varied surface topography of silver particies rnay inhibit

SESHG, especially since formation of silver oxides easily occurs. Ishida et al?'

concluded that the kinetics of MSA depend on the surface conditions of silver and gold.

Adsorption (both chemi- and physisorption) from various chemicai species do indeed

occur and rnay contaminate the surface. Somo jai et confimed that carbon

monoxide, oxygen, water and hydrocarbons chemisorb onto silver. In addition, Richter et

al? noted that water and hydrocarbons tend to physisorb ont0 silver. Thenfore,

adsorption of chernical species evidently does occur on the silver nanoparticle surface.

Therefore, the i2' response from SHG due to permeating SESHG electromagnetic waves

rnay not occur at d l . We have shown that the silver nanoparticles alone do not produce

any SHG signal. Similady, samples of residual ODMASP on underivatized silica glus

slides gave no SHG signal. We show that accidental adsorption of ODMASP in the

interstices between silver nanoparticles on the silica substrate cannot contribute to the

signal. Enhancements in i2' rnay be caused by resonance of surface plasmon modes at

the second hmonic wavelength. We descnbe this enhancement in the following. SHG

signal radiating from ODMASP pemeates into the silver particles to excite a plasma

response (see Section 1.1.4). We speculate that an excitational resonance occurs from a

coupled state between the plasma oscillations and the photons, therefore forming surface

plasmons. The plasmons focus and align electromagnetic fields of incident radiation into

the surrounding ODMASP layer. Pocluand et al? concluded that d2' becornes enhanced

on various silver surfaces. Consequently, the resulting surface plasmon resonance at the

silver-ODMASP interface enhances the XI2' response From SHG.

hfîuences on d2) i) Quaternization

Explanations for the differences in the i2' nsponse in our samples (see Table 2.4) may

be attributed to various factors including ODMASP molecular hyperpolarizability, self-

poling effkiency, local fields and number density. Park et al." surmised that an increase

in /la dye such as ODMASP may simply be accounted for by the effect of quaternization

of the pyridyl nitrogen. The increase in f l would therefore, increase the eficiency for

SHG. Other researchers do not account for an incnase in j from quatemization.

Therefore, whether or not quaternization is a factor in raising p remains questionable.

ü) Polar Order

Another explanation for the difference in the values of i2' obtained from the 2 systems

may be sought in the polar order of ODMASP on the silver nanoparticles. ODMASP self-

poles by van der Waals and electrostatic interactions. Cis alkyl tails promote hyàrophobic

van der Waals interaction among other alkyls. Porter et aL3* concluded from FT-IR and

electron diffraction experiments that stilbazole alkyl tails greater than Clo promote better

self-poling. Cross et al." concluded that Ci* self-poles the most efficiently using Ca, CIO

and C14 alkyl tails. In addition, Pincreases as alkyl carbon chah length increases from Ci

to Ci* (see Tables 3.2 and 3.3). This f l increase results from improved crystailization of

monomeric ODMASP. Ashwell et al?* confirmed that increases in Band i2' up to Czo

alkyl for stilbazoles in general such as ODMASP.

iii) Number Density

Local fields are associated with the dipole-induced-dipole interactions among monomeric

ODMASP for the MPTMS-silver-MAA-ODMASP heterostnicture. These interactions

affect the crystaiIization and thenfore, the ODMASP number density. High crystallinity

produces increased numbcr âensity and larger 8. Girling et al?' noted that increased

number density and fllead to an increase in the local fields. Steinhoff et al." observed

larger local fields in crystalline stilbazole venus monomeric stilbamle.

We speculate that the MPTMS-silver-MAA-ODMASP samples contain a low degree of

ODMASP crystallinity. Low crystailinity may be due to a number of reasons. Among

these reasons includes steric interactions as described by UlmanO4' A large free volume in

ODMASP occurs fkom the hydrocarbon Ci8 alkyl tail, which may lower the packing

efficiency leading to effective crystallization. Effectively, a lower y2' would result due to

a lower ODMASP number density. We calculated an estimated 1 .S ODMASP monomers

per nm2 on silver (assuming each ODMASP occupies a "foorprint" area of 54 nm2 on the

surface). Initidly, we assumed a hexagonal close-packing pattern. However, metal

particles aggregated into a fractal dimension as shown by the MFFïMS-silver-rnethyl-

BDMT-gold heterostmcture on TEM grids (see Figures 2.6a and 2.6b). We have yet to

ascertain if the MPTMS-silver-MAA-ODMASP heterostmcture on the silica glass OCB

slide shows fractal character as well. If we see a fracta1 dimension, then we may assume

that the number density of ODMASP on silver is much lower than previously estimated

since silver particles are pnsumably fractally (not hexagonally) distributed. By Our

estimation, there is a very low number density in the MPTMS-silver-MAA-ODMASP

heterostmcture compared to the PS-DMASP composite. We would othenvise assume that

the large DMASP number density in PS-DMASP would produce an exceptionally large

i2) - much 1-r than that for the MPTMS-silver-MAA-OMDAPS heterostmcture. This

consideration supports our conjecture that the fractal silver nanoparticle distribution

increases f ' . Andrews et al?' enhanced local fields of i3) in fracta1 silver nanoparticles

in poly(methy1methacrylate) composites. Since local fields may be enhanced up to 106

fiom fractal silver, we therefon assume that a sirnilar response in f2' of locai fields

occurs in the MPTMS-silver-MAA-ODMASP heterostructurc. From the data, we observe

a larger $' in MFTMS-silver-MAA-ODMASP even though the ODMASP number

density is much lower than expected. Therefore, we may conclude that local field

enhancement ofi2' occurs fiom the fractal silver nanopaiticles.

Conclusions

summery

New types of nano- and mesoscale multilayered composites were prepared. We

fabricated MPTMS-silver-methyl-BDMT-gold heterostructures and successfully used

XPS to follow the formation of each layer.

We concluded that BDMT and gold were not chernisorbed ont0 the silicon wafer. As

well, we monitored the sulf'ur S 2p doublet band to confirm the methylation and

chemisorption of colloidal silver, and the chemisorption of BDMT and colloidal gold.

Methylation was effective but did not envelop al1 the exposed M P T M S terminal

sulfhydryl groups. Monitoring of the silver Ag 3d doublet band showed that the band was

darnped after chemisorption of colloidal gold ont0 BDMT.

We confirmed by using TEM that colloidal gold nanoparticles could be chernisortted

selectively ont0 a colloidal silver nanoparticle sublayer. Gold chemisorbed exclusively on

top of silver by the BDMT spacer with no overlapping of pld-gold or silver-silver

nanoparticles. Colloidal silver and gold nanoparticles were measured to be 6.57 f 1 .O2

nm and 12.59 I0 .75 nm in diameter. respectively. We calculated the fractal dimension of

coiloidai silver to be 1.45 f 0.08. Following the addition of BDMT. colloidal gold

nanoparticles were imprinted and replicated into the fracta1 pattern of previously

deposited colloidal silver nanoparticles to occupy a fractal dimension of 1.76 f 0.13.

We also fabricated gold-BDMT and MPTMS-silverlgold-BDMT, MPTMS-silver-BDMT

and MPTMS-silver-methyl-BDMT-gold heterostructures on silica glass slides. Overall,

the W-VIS spectra revealed a silver surface plasmon absorbance blue-shifi due to a

coupled silver-gold charge transfer. We fabrîcated the MPTMS-silver-MAA-ODMASP

heterostmcture as well. We calculated the ODMASP number density in MPTMS-silver-

MAA-ODMASP (1.5 ODMASP per d) and in PS-DMASP (500 DMASP per nm2 in 1

pn thick film). Fuidly, we obtained a i2' of 1 A8 n 1 & J ~ (4.00 x 1 O-' esu) and 0.29

x IO-= Cfl2 (0.78 x 1 0 ~ esu), mspectively, for the 2 samples as well. The low number

density in the MPTMS-silver-MAA-ODMASP heterostructure points to a Low extent of

ODMASP crystallization (influencing P). The silver plasmon absorbance using W-VIS

spectroscopy revealed a nd-shift due to ODMASP. We postulated that resonant

excitations may be nsponsible for i2' enhancernents and proposed potential models.

Future Research

We suggest hirther improvements in design strategies for fabricating heterostnictures

incorporating siiver and gold nanoparticles and ODMASP. Proving enhancement of 2'' from silver rnay be made by the following:

1) Measure the 2*' of ODMASP or DMASP quatemized in poly(styrene),

2) Tune the laser wavelength into the piasmon band maximum to see if 2') increases as

the plasmon is excited,

3) Use a squaraine dye that does not absorb at 532 nm (second harmonie).

References

' (a) M. Pomerantz, A. Segmuller, L. Netzer, J. Sagiv, Thin Solid F i l m 132, 153- 162

(1985); (b) R. Maoz, J. Sagiv, Langmuir 3, 1034-1044 (1987); (c) S. R. Wasserman, Y.

-T. Tao, G. M . Whitesides, h g m u i r 5, 1074-1087 (1989); (d) D. A. Stenger, J. H.

Georger, C. S. Dilcey, J. J. Hickman, A. S. Rudolph, T. B. Nielsen, S. M. McCort, J. M.

Calvert, J. Am. Chem. Soc. 114,8435-8442 (1992); (e) Z. Yang, H. Yu, Adv. Mater. 9,

2 J. A. Creighton, C. G. Blatchford, M. G. Aibrecht, Chem Soc. J. Faraday Trans. II 75,

D. A. Weitz, Surf: Sci. 158, 146 ( 1985).

J. Baldwin, N. Schühler, 1. S. Butler, M. P. Andrews, Langmuir 12,6389-6398 (1996). * J. P. Gao and G. D. Darling, J. Am Chem. Suc. 114,3997-3998 (1992).

1. W. Rabalais, Principles of Ultravioler and Photoelectron Spectroscopy, Wiley,

New York, 1977, pp. 349.

' P. E. Laibinis, O. M. Whitesides, D. L. Allara, Y. Tao, A. N. Parikh, R. G. Nuuo, J.

Am. Chem Soc. 113,7152 (1991).

S. Leavell, J . Steichen, J. L. Frankiin, J. Chem. Phys. 59,4343 (1973).

C. D. Wagner, P. Bilan, Surf: Sci. 35,82-95 (1973).

'O R. H. Doremus, J. Chem Phys. 40,2389-2396 (1964).

' * J. Turkevich, G. Garton, P. C. Stevenson, J. Culloid. Sci. 9,26-35 ( 1954).

l2 A. R. West, Solid State Chemistry and its Applications, Wiley, New York, pp. 59-69,

1984.

l3 M. P. Andrews, T. Kanigan, W. Xu, M. O. Kuzyk, SPIE Proc. 2042,366 (1994).

l4 A. DL. Barabbi, H . E. Stanley, Fractal Concepts in Surface Growth, Cambridge

University Press, Cambridge, UK, 1995, 175-191.

l5 G. Chumanov, K. Sokolov, B. W. Gregory, T. M. Cotton, J. Phys. Chem. 99,23

(1995).

l6 L. -T. Cheng, W. Tarn, S. H. Stevenson, G. R. Mendith, G. Rikken, S. R Marder, J.

Phys. Chem. 95,10631 (1991).

" G. H. Cross, N. A. Cade, 1. R. Girling, 1. R. Peterson, D. C. Andrews, J. Chem Phys.

F. C. Bohren, D. R. Huffinan, Absorption und Scatiering of Light by Smnll Parricles,

Wiley, New York, pp. 228,265,326-369 (1983).

l9 U. Kreibig, J. Phys. F: Met. Phys. 4,999 ( 1974).

20 G. Decher, J. D. Hong, J. Schmit, ThUi Solid Films 211,831 (1992).

21 2. Xu, W. Lu, P. W. Bohn, J. Phys. Chem. 99,71547159 (1995).

M. A. Glass, P. F. Liao, J. G. Bergman, D. H. Olson, Opt. Lon. 5,368-370 (1980). 23 H. G. Craighead, A. M. Glass, Opt. Lett 6,248-250 (198 1 ). 24 C. F. Eagen, Appl. Opt. 20,3035-3042 (1996). 25 P. D. Maker, R. W. Terhune, M. Nisenhoff, C. M. Savage, Phys. Rev. Le#. 8.21

(1 962).

26 J. Jerphagnon, S. K. Kurtz, J. Appl. Phys. 41, 1667 (1970).

" P. K. Tien, R. Ulrich, R. J. Martin, Appl. Phys. Let?. 17,447 (1970).

" T. J. Marks, M. A. Rainer, Angew. Chem. Inr. Ed. Engl. 34, 155-173. (1995).

29 A. C. R. Pipino, R. P. Van Duyne, G. C. Schatz, Phys. Rev. B 53.7 (1996).

'O P. F. Brevet, Surface Second Humonic Generation, Press Polytechniques et

Universitaires Romandes, Lausanne, France. 1 15-144 (1997).

A. R. McGurn, T. A. Leskova, V. M. Agranovich, Phys. Rev. B 44, 11441 (1991).

'' 2. Sekkat, W. Knoll, SPIE Proc. 2988, 164- 184 (1997).

" T. Ishida, S. Tsuneda, N. Nishida, M. Hara, H. Sasabe, W. Knoll, Langmuir 13,4638-

4643 (1987). 34 M. A. Chester, G. A. Sorno rjai, Surf: Sci. 52,21 (1975).

35 J. Richter, L. Stolberg, J. Lipkowski, h g m u i r 2,630 (1986).

36 (a) 1. Pockrand, A. Brillante, D. Mobius, J. Chem. Phys. 77,6289 (1982); (b) 1. R.

Girling, N. A. Cade, P. V. Kolinsky, G. H. Cross, L R. Peterson, I. Phys. D 19,2065

(1986).

" I. H. Moon, J. U. Choi, J. H. Kim, H. Chung, J. H. Hahn, S. B. Kim, J. W. Park, J.

Mater. Chem 6(3), 365-368 (1996).

38 M. D. Porter, T. B. Bright, D. L. Man, C. F. D. Chidsey, J. Am. Chem. Soc. 109,3559

(1987).

39 1. R. Girling, N. A. Cade. P. V. Kolensky, G. H. Cross. 1. R. Peteaon, J. Phys. D 19,

2065 (1986).

" R. Steinhoff, L. F. Chi, G. Mamwsky, D. Mobius, J. Opt. Soc. Am. B 6.843 (1989).

41 A. Ulman, An Introduction to Ultrathin Orgonic Films - Part 3, Acadcmic Press.

Boston, MA 199 1.

a (a) M. P. Andrews, M. G. Kuzyk, F. Ghebrernichael. Nonlinear Optics 6, 103- 1 12

(1993); (b) M. P. Andrews, T. Kanigm, W. Xu, M . G. Kuzyk, SPIE Proc. 2042,366

(1994).

Chapter 3

Introduction

3.1.1 NLOD Alternative - NDPEPD In this chapter, we design an NLOD to follow some of the MSA principles outlined in

Chapter 1. We reiterate Our objective here. We describe the synthesis of a novel NLOD

(NDPEPD tolane) that chemisorbs directly ont0 silver or gold nanoparticle surfaces

without the use of a spacer.

Tolanes are ngid linear structures that self-align very efficiently onto OCBS.' In general,

NLODs can be chemisorbed to fom heterostructural OCBs. in our structures, we initially

chose ODMAPS to use in the MPTMS-silver-MAA-ODMAPS. We capitalized on self-

poling since it is driven by the hydrophobic interactions associated with the hydrocarbon

alkyl tail. Self-poling circumvents electrical field poling to bnng about alignment for i2'. Several factors are important to ODMAPS chernisorption. orientation and optical

response. Solvent polarity and hydrogen bonding are important. In addition, polarity and

hydrogen bonding affect the excited state. For example. polar solvents stabilize the

excited state more than the ground state? As stated pnviously, Darling et al.' used a

methanol-toluene (1 :9 v/v) solvent mixture to chemisorb ODMAPS onto an MAA spacer.

Care must be taken to controi the pH of the medium since the pyridinium nitrogen may

be protonated by water (in methanol) prior to the acid-base interaction with ODMAPS-

MAA. Therefore, speculations arise in the nliability of ODMAPS chernisorption ont0 the

MAA spacer.

As an aitemative to ODMAPS, we proposed the use of N4[(4'-nitrodiphenylethyny1)-

phenyll-bis-2"-diethanethiolamine (NDPEPD), which could chemisorb directly onto the

siiver surface by the sulfhydryl group without the use of any additional spacer. We

surmise that this alternative circumvents the diff'icuity associated with spacer

incorporation into the heterostructue. Consequently, a more extensive chemisorption of

the NLOD ont0 the silver surface may be possible with NDPEPD. The availability of the

disulfhydryl groups allows for an increased degree of chemisorption ont0 the silver

surface. Contrarily, ODMAPS only has a monosulfhydryl group from the MAA spacer

for chernisorption. Therefore, NDPEPD has a larger probability of chemisorption ont0

the surface than ODMAPS. As well, NDPEPD can self-pole by MSA more eficientiy

than ODMAPS. ODMAPS bas Cia carbon alkyl tails that are dependent more extensive1 y

on kinetics and themodynamics to promote aiignment. NDPEPD pz-orbital interactions

occur between adjacent phenyl groups of monomeric NDPEPD. Such interactions may

lead to phenyl x-r stacking of NDPEPD? In contrast to ODMAPS, NDPEPD has no

stenc interactions from the Cl* carbon alkyl tails with which to contend. ODMAPS has a

hydrophobie Cla alkyl tail that cm sterically interfere with self-poling due to the large

imposed free volume. On the contrary, NDPEPD cm aggregate and pole due to linear

molecular rigidity. A detailed discussion comparing NDPEPD and ODMAPS. as well as

addressing the advantages of NDPEPD will be discussed later (Section 3.3.2). Now, we

will explore and propose the preparation of NDPEPD next.

3.13 NDPEPD Tolane Dye Synthesis

The preparation of N4-[(4-nitrodiphenyIethynyl)phenyl)phenyl]-bis-2"-die~mehiol-

amine (NDPEPD) was carried out according to Figure 3.1.

OH PDEA

PdlP(C6Hdh (2 mol 96) Cul (2 mol %) diùopmpylamine 8S0 C

Figure 3.1: Schematic - NDPEPD synthesis

N-phenyldiethanolamine (PDEA) was iodinated to form [ I l from the aryl amine

according to the procedure of ~rewster? The hydroxyl group in [ I l was protected by both

acetylation6 and silanation? Purified [3] was synthesized and palladium-catalyzed cross-

coupling of [2a] and [2b] each with [3] was perfomed to produce [4a] and [4b] as

described by Mardcr et d8 The hydroxyl group in [4] was deprotected by deacety1ation9

and desilanation.1° Thiolation was performed to convert hydroxyl to sulfhydryl according

to the procedure by ~ishio" involving Lawesson's nagent to form [6]. Conversion of

hydroxyl to suLfhydry1 fier crosscoupling instead of before was perfonned to prevent

contamination of the palladium catalyst.12 The triphenylphosphine ligands on the

palladium metal center easily absmcts sulfur from thiosulfates and thi~alk~ls . '~

Therefore, protection of hydroxyl by sulfhydryl is not feasible in these circumstances.

Sulfhydryl may be easily removed and chemisorbed onto the catalyst surface. Mfication

of [2] to [6] was accomplished by flash column chromatography with silica using hexane-

ethylacetate or methanol-dichloromethane as the eluting solvent mixture.

3.2.1 IPD and IPTE - Aryl Iodkie Spthesis

[l] 4-iodop hen y ldiethmolamine

Materiais

iV-phenyldiethanolamine (97%), sodium bicarbonate (99.7 + %), iodine (99.999 + %),

chloroform (99.8 56) and sodium hydroxide (97 96) were obtained from Aldrich

Chernical. Methanol(99.5 + %) was obtained from Caledon Laboratones. Al1 chernicals

were used without further purification.

Method

N-phenyldiethanolamine (PDEA) (120 rnrnol, 2 1.75 g) and sodium bicarbonate

( 1 80 mmol. 1 5.12 g) were measund into a 100 mL round bottom fias k and dissolved in

methanol(20 mL). The flask was cooled to 10-15' C in an ice bath and the cream-white

solution was stirred for 5 minutes. Distilled water was added and the solution was stirred

for an additional 20 minutes. Iodine (100 mmol, 25.38 g) was slowly added. The olive-

yellow solution was stirred for another 30 minutes. Cnide [1] was collected as a matte-

black viscous oil on a Buchner funnel under vacuum. Chloroform was added to dissolve

crude [l], which was extracted using a separatory funnel. Dilute sodium hydroxide

solution (10 % w/v) was added to separate [1] in the organic phase from ammonium salts

in the aqueous phase. The organic phase was isolated and the solvent was removed using

a rotating evaporator under vacuum. Charcoal-black crystals were produced in yield:

30.22 g (82 %). MS ml2 307 (m, 263 (MC - 1-C&N(CH2-H)), 18 1 (AC - C a -

N(CH2CH20H)2). 45 (M+ - CH2CH20H); MS mh calcd for Ci&Ii402NI: 307.00; Found:

306.71. 'H NMR (CDCi3: 6 3.54 (t, 4H. -NC&on arnino, J = 5.00 Hz), 3.81 (t, 4H,

- C w - on arnino, J = 5.20 Hz), 6.46 (d. 2H, -CEJOL on phenyl, J = 9.20 Hz), 7.45 (d,

W, Ica- on phenyl, J = 9.00 Hz) ppm. Anal. Calcd for C1&402M: C, 39.10; H, 4.59;

N, 4.56. Found: C, 41.27; H, 5.01; N, 4.84.

[fa] 4-iodophenyi-bk-2'dethyletb8tloaty1amine or IPD

Materials

Acetic anhydride (98 %), 4dimeihylaminopyridine (DMAP) (99 + %), and pyridine

(99 + %), ethanol(95 %), ethylacetate (99.5 + %), sodium sulfate (99 + 8) were obtained

from Aldrich Chernical and used without further purification. Toluene (99.8 %) was

obtained from Caledon Laboratories.

M e a d

Purificd [l] (1.00 mmol, 0.291 g), acetic anhydride (2.50 rnmol, 0.32 mg) and DMAP

(10 mg) were measured into a 100 mL round bonom flask and dissolved in pyridine

(50 mL). The solution was stirred for 1 hour at room temperature and later transferred to

a separatory hinnel. Ethanol(10 mL), ethylacetate (10 mL), water (10 mL) and potassium

carbonate (17.5 mmol, 2.02 g) were added and extracted in succession (in the aqueous

phase). The organic phase was isofated and the ethylacetate nmoved by rotating

evaporator under vacuum. Toluene was added to assist removal of pyridine and crude

[2a] was dried over sodium sulfate. Cnide [2a] was separated and purified by flash

column chromatography on silica (70-230 mesh) using hexane-ethylacetate (4: 1,3: 1 and

2: 1 V/V in sequence) as the eluting solvent. The procedure is described at the end of the

section. A peach-orange powder was obtained in yield: 0.25 g (65 %). MS rnh 39 1 (m, 26 1 (M+ - I-C&-N(CH2CH2-0)2), 84 (M+ - CH2CH2-O-COCH& MS m/z calcd for

CLaLB0W: 391.14; Found: 391.15. 'H NMR (CDC13): S 2.04 (s, 6H, -C& on acetyl),

3.59 (t, 4H, -NC&- on amino. 1 = 6.30 Hz), 4.2 1 (t, 4H, -C&û- on amino, J = 6.10 Hz),

6.56 (d, 2H, --CN- on phenyl, J = 9.00 Hz), 7.47 (d, 2H. 1CCI-J- on phenyl. J = 9.20

Hz) ppm. Anal. Calcd for Ci&804h?k C. 43.00; H, 5.41; N, 4.18. Found. C, 43.23; H.

5.56; N, 4.25.

Materials

Terr-butyldimethylsilyl (TBMDS) chloride (97 8). triethylamine (99 + %),

4-dimethylaminopyridine (DMAP) (99 + 96). and dichloromethane (99.6 %) were

obtained from Aldrich Chemical and used without hirther purification.

Methoà

Purified [l] (3.49 m o l , 1.02 g), TBDMS chloride (16.2 mrnol. 2.45 g), triethylarnine

(19.5 mmol, 1.97 g), DMAP (10 mg) and dichloromethane (25 mL) were combined in a

100 mL round bottom flask and stined for 12 hours. Chloroform, distilled water and

dilute hydrochloric acid were added to neuulilize excess triethylarnine. Cnide [2b] was

isolated by rernoval of triethylammonium salts in the aqueous phase by separatory Funnel

and the organic phase was removed by rotating evaporator under vacuum. Cnide [2b] was

separated and purified using flash colurnn chromatography on silica (70-230 mesh) using

methanol-dichloromethane ( 1 9 vlv) as the eluting solvent. The procedure is descnbed at

the end of the section. A cherry-nd powder was obtained in yield: 1.42 g (76 %). MS rn/z

535 (m, 409 (M+ - C&+QCH~CHI-O-S~(CH~)~C(CH~)~)~), 334 (M+ - N(CH2CH2-O-

Si(CH3)2C(CH3)3)2), 3 1 8 (M+ - C&-N(CH2CH20Si(CH3)2)). MS mlz calcd for

C&,&NISi2: 535.18; Found: 535.13. 'H NMR (CDCI,): 6 0.03 (s, 12H. -C& on

methyl), 0.89 (s, f8H, -C& on ter?-butyl), 3.45 (t, 4H. -NC&- on amino. J = 6.40 Hz),

3.70 (t, 4H, -C&O- on amino, J = 6.10 Hz), 6.45 (d, 2H. =aCN- on phen y 1.3 = 9.20

Hz), 7.40 (d, 2H, ICCH- on phenyl, J = 9.20 Hz) ppm. And. Calcd for C2H4202NISil: C,

49.33: H, 7.90; N, 2.62. Found: C, 51.78; H, 8.54; N, 2.71.

33.2 NEDPA - Aryl Ailcyne Synthesis

[3] 4-nitro4'=ethynyldiphenylacetylene or NEDPA

Materials

1-nitro4iodobenzene (99.8 %), 2-methyl-3-butyn-2-oI(99.5 4b). palladium dichiorodi-

(triphenylphosphine) (99.5 %), diisopropylamine (99 $6). sodium hydroxide (97 45). and

1,Lkliiodobenzene (99.5 %), toluene (99.8 96) were obtained from Aldnch Chemical.

Cuprous iodide (99.999 Q) was obtained from Fisher Scientific. Toluene and

diisopropylamine were further distilled from calcium hydride and dried over sodium

under a nitrogen atmosphere.

Meîhoà

Purified [3] was synthesized and obtained from Professor T. B. Manier, University of

Waterloo, Waterloo. ON. 1 -nitro4iodobenzene (1 .ûû mmol, 0.23 g), 2-rnethyi-3-butyn-

2-01 ( 1 .O rnrnol, 0.76 mg), palladium dichlorodi(tripheny1phosp hine) (PDCDTPP)

(2 mol %) and cuprous iodide (2 mol 96) were added to a triple-necked 50 mi, round

bottom flask under an argon atmosphere in a glove box. The top-middle and top-left flask

openings were attached to a condenser and a Schlenk line apparatus. respectively.

Diisopropylamine (20 mL) was added through a septum into the top-right opening by

syringe under a nitmgen flow. The solution was refluxed for 15 minutes and solvent was

later cannulated under a nitrogen flow. Sodium hydroxide (15.6 mmol, 0.50 g) was

dissolved into toluene (50 mL) and added into the top-right opening through a septum by

syringe under a nitrogen flow. The naction was refîuxed for an additional 15 minutes and

cmde ethynylbenzene (0.8 1 mmol, 0.1 1 g) was isolated. Solvent was cannulated under a

nitrogen flow. I ,4diiodobenzene (2.43 mrnol, 0.79 mg), PDCDTPP (2 mol a), cuprous

iodide (2 moi %) and diisopropylamine (20 mL) were added to the triple-necked 50 m .

round bottom flask under the same previous conditions. The solution was refluxed for 15

minutes to form 1 -iodo4(4'-nitrophenylethyny1)benzene. Al1 the previous procedures

were repeated to produce 131. Solvent was rernoved and crude [3] was extracted into hot

toluene and filtend through a pad (2 cm deep) of silica gel (70-230 mesh). A lemon-

yellow powder was obtained in yield: 0.18 g (71 96). MS mlz 247 (M+) 2 17,200. 189,

174, 153, 136, 105.89.77. MS rn/z calcd for Ci&02N: 247.06; Found: 246.80. 'H

NMR (CDC13): 6 3.21 (s, lH, =Cg on terminal ethpyl), 7.5 1 (s, 4H, = C C - and - CHCC= on phenyl near to terminal ethynyl), 7.66 (d, 2H, -ClJCC= on phenyl near to

center ethynyl, J = 8.85 Hz), 8.22 (d, 2H, -NCW- on phenyl near to nitro, J = 9.03 Hz)

ppm. Anal. Calcd for C1&O2N: C, 77.72; H. 3.67; NT 5.67. Found: C, 78.48; H, 3.70; N,

4.81.

33.3 IPD and IPTE with NEDPA - Palladium-catalyzeà Cross-coupiing

Materiais

Palladium tetra(tripheny1phosphine) (99.9 9) and diisopropylarnine (99 Sb) were

obtained from Aldrich Chernical. Cuprous iodide was obtained from Fisher Scientific

(99.999 %). Diisopropylamine was further distilled from calcium hydride and dned over

sodium under a nitrogen atmosphere.

Method

Coupling of [îa] with [3] to form [4a] was performed. Palladium tetra(inpheny1-

phosphine) (PT'ïPP) was measured (2 mol %) under an argon atmosphere in a @ove box

and deposited into a triple-necked 50 mL round bottom flask equipped with a condenser

(located on the top-middle opening) and sealed with a septum. [2a] (2.96 mmol, 1.59 g)

was added into a 25 mL side-amed flask. Diisopropylamine (5 mL) was added by

syringe under a nitrogen atmosphen and the solution was bubbled under a nitrogen flow

by syringe needle for 20 minutes. Cuprous iodide (2 mol 46) and 4nitro-4'-ethynyldi-

phenylacetylene (1.19 mmol. 0.50 g) were carefhlly added to the topright opening of the

flask while under a nitrogen flow. [2a] was canaulated and added into the flask at a rate

of 1 &op per second under a nitrogen flow. Diisopropylamine (15 rnL) was used to rime

the inside of the flask. The solution was refluxed for 10-15 minutes and the diisopropyl-

amine solvent was removed under vacuum. Cnide [4a] was separated and purified by

flash column chromatography with silica (70-230 mesh) using hexane-ethylacetate (4: 1 to

2: 1 vlv). The procedure is described at the end of the section. An orange-yellow powder

was produced in yield: 1 .O3 g (73 %). 'H NMR (CDC13): 6 3.66 (t. 4H. -NC&- on amino,

J = 6.10 Hz). 4.24 (t, 4H, - C w - on amino. J = 6.10 Hz), 6.72 (d. 2H, -CHCN- on

phenyl near to amino. J = 8.53 Hz), 7.39 (d, 2H, -CCCIJ- on phenyl near to amino.

J = 8.3 1 Hz), 7.50 (S. 4H, S C C E - and -=Ck on center phenyl), 7.65 (d, 2H, -ECCE

on phenyl near to nitro, J = 8.53 Hz), 8.22 (d, 2H, -NCCH- on phenyl near to nitro,

J = 8.3 1 Hz) ppm. Mass spectrometric and elemental analyses were not completed for

[4a] due tu distorted mass spectra resulting from product decomposition.

Materiais

Palladium tetra(tripheny1phosphine) (99.9 %) and diisopropylamine (99 %) were

obtained from Aldrich Chernical. Cuprous ioâide (99.999 %) was obtained from Fisher

Scientific. Diisopropylamine was further distilled hom calcium hydnde and dned over

sodium under a nitrogen atmosphere.

Method

Coupling of [2b] with [3] to form [4b] was followed from the previous procedure. Cnide

[4b] was separated and purified by flash colurnn chromatography with silica (70-230

mesh) using methanoi-dichloromethane (1 :9 v/v). The procedure is described at the end

of the section. An orange-nd powder was produced in yield: 1.32 g (68 46). MS rn/z 655

(m, 535 (MC - CC-CaH4-CC-C&N(CH2CH2-O-Si(CH3)2C(CH3)3)2)), 409 (W - C a - N(CH2CH2-O-Si(CH&C(CH3)3)2), 147 (M+ - 02N-Cd&-CC); MS mlz calcd for

C3&1500,@2Si2: 654.33; Found: 654.41. 'H NMR (mg): 6 0.03 (S. 4H. -CE& on

methyi), 0.86 (s, 18H, CH3 on rert-butyt), 3.47 (t, 4H, -NC& on amino, J = 0.04 Hz),

3.72 (t, 4H, -CHHO- on amino, J = 0.04 Hz), 6.47 (d, 2H, -CIJCN- on phenyl near to

arnino, J = 0.05 Hz), 7.3 1 (d, 2H, - C C - on phenyl near to amino, J = 0.05 Hz), 7.50 (s,

4H, <CC- and -Cm& on center phenyl), 7.69 (d, 2H, - C C - on phenyl near to

nitro, J = 0.05 Hz), 8.25 ( d 2H, - N C - on phenyl near to nitro, J = 0.06 Hz) ppm. Anal.

Calcd for C38H500&2Siz: C, 69.69; H, 7.69; N, 4.27. Found. C. 69.93; H, 7 3 5 ; N, 4.30.

3.2.4 NDPEPD - Direct Thiolation

Materiais

Methanol(99.9 %) was obtained frorn Caiedon Laboratones. Chloroform (99.8 96).

potassium carbonate (99.99 %), tetrabutylammoniurn chloride (TBAC) (99 + 96) and

sodium hydroxide (97 + %) were acquired frorn Aldrich Chemical md used without

further purification.

Method

Puiified [4a] (2.23 mmol, 1 .O3 g) was added into a 100 mL round bottom flask and

partially dissolved in methanol-chloroform-water ( 1 : 1 : 1 v/v/v). Potassium carbonate

(3.62 mmol, 0.5 g), TBAC (4.44 mmol, 1.23 g) and sodium hydroxide (2.08 mmol,

0.10 g) were added. Unfortunately, decomposition of [4a] did not permit further analysis.

Materials

Teinmethylammonium fluoride (TMAF) tetrahydrate (98 %) in acetonit.de (99 + %),

methanol(99.9 %), toluene (99.8 96) and hydrochloric acid (37 % wlv) were acquired

from Aldrich Chemical.

Method

Purified [4b] (2.12 mmol, 1.32 g) was added into a 100 mL round bottom flask and

dissolved in TMAF tetrahydrate. A methanol-toluene (5: 1 vlv) solution and h ydrochloric

acid (0.5 rnL) were added and the solution was heated to SOO C. Solvent was removed

using a rotating evaporator under vacuum. Cnide [Sb] was separated and purïfied by

silica gel flash column chromatography (70-230 mesh) using hexane-ethylacetate (4: 1 to

2:1 v h ) . The procedure is described at the end of the section. A cherry-red powder was

produced in yield: 0.92 g (82 %). MS m/z 426 (M+), 379 (M' - Cs&çC-C6&-cC-C6H4-

N(CH2CHtOH)2), 305 (W - CC-C&-CC-C&-N(CH2CH20H)z), 28 1 (M+ - C A - C C -

Ca)4-N(CHzCHzOH)2), 146 (M+ - 02N-Cd&-CC); MS mlz caicd for Cz&IuO&:

426.16; Found: 426.45. 'H NMR (CDC13): 6 2.10 (s, 2H, broad terminal OH), 3.5 1 (t, 1H,

-NC&- on arnino. J = 6.10 Hz), 3.76 (t, 4H, -C&O- on amino, J = 6.10 Hz), 6.69 (d, 2H,

-CEJCN- on phenyl near to arnino, J = 8.54 Hz), 7.23 (d, 2H. =CCC& on phenyl near to

arnino, J = 8.30 Hz). 7.39 (s, 4H, S C C H - and -CHCC= on center phenyl), 7.65 (d, W ,

-CHCCs near to nitro, J = 8.54 Hz), 8.21 (d. 2H, -NCC& near to nitro, J = 8.30 Hz)

ppm. Anal. Calcd for C26HZo4N2: C, 73.24; H. 5.20; N, 6.57. Found. C, 73.48; H. 5.60;

N, 6.8 1.

[a] N4-[(4'-nitrodiphenylethynyl)phenyl]-b&-2"die~me~iola~e or NDPEPD

Materiais

2.4-bis-(4-methoxypheny1)- 1,3,2,4-dithiadiphosphetane 2,4disulfide (Lawesson's

reagent) (97 %) in toluene was obtained fiom Aldrich Chemicai.

Met hod

[Sb] was converted to [6] by direct thiolation. Lawesson's reagent (5.86 mmol, 0.8 1 g)

and [Sb] (2.37 mmol, 0.18 g) were added under an argon atmosphere in a glove box and

deposited into a triple-necked 50 mL round bottom flask equipped with a condenser

(located on the top-middle opening). Toluene (20 mL) was added by syringe under a

nitrogen atmosphere and the solution was s h e d for 24 hours under a nitrogen

atmosphere at room temperature. Toluene was cannulated under a nitrogen flow. Cnide

[6] was separated and purified by silica gel flash column chromatography (70-230 mesh)

using toluene-methanol(2: 1 to 1: 1 vlv) to produce an orange-brown powder in yield:

0.73 g (70 96). MS m/z 458 (M?), 424 (M+ - HzS), 246 ((W - C&-N(CHZCH~SH)~); MS

m/z caicd for C&IUO~N~S~: 458.1 1; Found: 458.12. 'H NMR (CDC13: 6 1.33 (s, 2H,

broad terminal -Su, J = 6.15 Hz), 3.76 (t, 4H, -NC& on amino, J = 6.10 Hz), 4.06 (t,

4H, -Cas- on amino. J = 6.10 HZ), 6.69 (d, 2H, -CuCN- on phenyl near to amino,

J = 8.54 HZ), 7.42 (d, 2H. -CCCI-J- on phenyl near to amino. J = 8.30 Hz), 7.51 (s, 4H,

=CCCH- and -CHCG on center phenyl), 7.65 (d, 2H, -CHCG near to nitro, J = 8.54

Hz), 8.23 (d, 2H, -NCCH- near to nitro, J = 8.30 Hz) ppm. Anal. Calcd for

C ~ ~ H Z O ~ N ~ S ? : C, 68.1 1 ; H, 4.84; N, 6.1 1. Found. C, 68.65; H, 4.95; N, 6.16.

Süica-Gel Column Preparation for Flash ~hromatography'~

Materials

Hexane (98.5 %). ethylacetate (99.5 + %), silica gel (75-230 mesh), chloroform (99.8 %),

methanol(99.8 %), dichloromethane (99.6 %) were obtained from Aldrich Chernical and

used without further purification.

Method

Hexane-ethylacetate (4: 1 v/v) was added into a flask containing the dry silica gel to

produce a white slurry. The silica gel was transferred to a glass column (4 cm - inner

diameter) and filled to at least 30-50 cm in depth. Solvent levels were always maintained

above the silica gel level to provide efficient separation dunng elution. A sand layer

(0.5 cm) was placed on top of the silica gel after allowing the silica gel to settle. The

solvent level was lowered to just above the sand level layer. Chloroform was used to

dissolve the product and the solution was then carefully transferred into the colurnn by

Pasteur pipette. Hexane-ethylacetate was carefully added beginning with 4: 1 v/v portions

(NOTE: methanol-dichloromethane was used in some cases). Gradually. 3: 1 and 2: 1 v/v

portions were added as the separation proceeded. Fractions were collected in test tubes

and simultaneously anaiyzed with thin layer chromatography (70-230 mesh) using the

same eluting solvent. The product was isolated by cornparhg the starting material to the

gathered fractions. Fractions containing the product were collected and solvent was

removed by rotating evaporator under vacuum.

3.2.5 NDPEPD in Poly(styrene)

Su bs trates

ITO-glass slides (25 x 37.5 x 1 mm - 100 #square surface resisitivity - coated on one

side) were obtained from Delta Technologies, Ltd. Slides were taped on the coated side to

allow for an exposed electricai contact area to apply a voltage for corona discharge

poling.

Materials

NDPEPD was synthesized by us and used after final purification. Polystyrene (MW

45000) was obtained from Aldnch Chernical. Methanol(99.9 96) and toluene (99.8 %)

were obtained from Caledon Laboratones and used without hirther purification.

Method

Poly(styrene) (PS) (2.68 x IO-' mol, 1.210 g) was measured into a 5 D m glass viai and

dissolved into a methanol-toluene solution (1:4 v/v). NDPEPD (1 .O mol Z) was dissolved

into the PS-methanol-toluene solution and stirred with a magnetic stir bar. Continuous

stimng was rnaintained for 1 hour. The solution was filtered through a 0.2 mm ~crodisc@

CR PTFE filter (Gelman Sciences) into another 5 Dram glass vial. The solution was

dipensed ont0 an iT0-glass slide (onto the ITO-coated side) using a Pasteur pipette and

spin-coated at 1500 and 2000 rpm for 30 seconds using a photo-resist spin-coater

(Headway Research) to produce films of thickness 1-3 m.

Mass spectrometry was perfonned using an MS25RFA mass spectrometer (Kratos

Analytical Instrumentation) with a source temperature of 250°C and a 70 eV source

voltage. 'H NMR spectroscopy was recorded using the Gemini-200 NMR (Bruker

Instruments) at 200 MHz resonance frequency. 'H chenilcd shifis were nferenced to the

intemal standard tetramethylsilane (TMS) and d l spectra were recorded in deuterated

chloroform (CDC13). Elemental analyses were conducted using a 240 XA elementd

analyzer (CEC Instruments) in the Department of Chernical Engineering, McGill

University. Montréal, PQ. Film thickness was measured using a Dektak (Sloan

Technology) profilorneter provided by the Photonics Research Group, École

Polytechnique de Montr&d, Montréal, PQ. Electncal poling by electrical point corona

discharge poling at elevated temperatures was followed from Monazavi et al." and was

performed simu1taneously with SHG measurement for i21Z' nonlinear optical susceptibility

(see Figure 2.4). Samples were heated to 150' C over a 40 minute interval with an

electrical field of 4.0 kV (1.0 cm tip-to-piane gap) and cooled to room temperature over a

30 minute interval. SHG measurements for determining i2' was performed using a

Quanta-Ray DCR Q-switched neodymiurn-doped yttrium-aluminum gamet (Nd:YAG)

laser (output A = 1064 nm) with a 10 ns pulse width at 5 ml, a 10 Hz repetition rate and

equipped with optical lens components (Oriel Instruments). Sarnple and z-cut quartz

reference mounts (Oriel Instruments) with rotating speed 2' per minute from O - 60°.

photomultiplier tubes (PMTs) (Harnatsu Company) and duai-channel boxcar integrators

(Stanford Company) were used. The SHG signal was recorded from -50' to +50° for the

quartz reference and from O to 60" for the sample, and amplified using PMTs and

averaged using the boxcar integrators. Maximum 22' was calculated using Microcaic

Origina 3.73 software. Al1 rneasurements were performed in the Materials Research

Center and the Department of Physics and Astronorny, Northwestern University,

Evanston, IL.

Results and Discussion

3.3.1 Synthesis - NDPEPD

Iodination of N-phenyldiethanolamine (PDEA) was initially perfomed by dissolving

PDEA into methanol instead of water to improve solubility. Sodium bicarbonate extracts

hydrogen iodide to form sodium iodide and water (favorable equilibrium to prevent

hydrogen iodide formation - reduction). Further purification of [1] is necessary since

PDEA was not initial1 y purified (recrystailized).

The exposed hydroxyl groups in [ I l required protection. Acetic anhydride was used to

acetylate PD hydroxyl in the presence of pyridine base and catalytic DMAP? DMAP is

104 times more active as an acetylation cataiyst than pyridine alone.l6 Nucleophilic

addition of hydroxyl at carbonyl (acetic anhydride) gives the acetyl ester [2a]. Another

method for acetylation includes using acyl chloride in pyridine.'7 Similarly, TBDMS

chloride was used to silanate PD by reacting with catalytic DMAP in pyridine base.

Nucleophilic addition of hydroxyl to the silicon cation forms the silyl ether [2b]. TBDMS

is useful for a wide range of alcohols and is more stable to hydrolysis than trimethylsilyl

or dimethylisopropylsilyl ether. Other methods for silanation include using imida~ole~~

and dilithium s~lfide.'~

Palladium-cataiyzed cross-coupling of [2a] and [2b] each with [3] produce [4a] and [4b].

PTTPP catalyst initiates and propagates the cataiytic cycle.21 ~ d * reduces to pd0 by

oxidative coupling of [3]. P'iTPP oxidizes by addition of [2a] or [2b] but the presence of

thiol during coupling forms disulfide bridges by oxidative coupling. Consequenily, sulfur

contaminates PTTPP catalyst and depresses yields. Tram-metallation is performd by

reductive elimination of [4a] or [4b] and ETTPP is qenerated."

Deacetylation was used to deprotect acetylated hydroxyl (ester). Insolubility of [4a] in

methanolthloroforrn-water prevented deacetylation. Phase iraasfer TBAC improved

deacetylation at the aqueous-organic interface. Potassium carbonate was added initially to

deacetylate the [4a]? However, deacetylation was inhibited by insolubility of [4a].

Therefore, sodium hydroxide was added to aid in acetyl removal. Unfominately, [4a]

decornposed soon thereafter, and ammonium salts precipitated. Another method for

deacetylation involving potassium cyanide in ethanol for transesterification may have

been possible.u Nevertheless, rnilder conditions were necessary to remove acetyl. Thus,

we turned to TBDMS since deprotection procedures were extremely mild and limited the

risk for decomposition of product.

Desilanation ruas used to deprotect silanated hydroxyl (silyl ether). A common approach

used €or mild desilanation involves TBAF tetrahydrate in THF. Unfortunately, gelation

occurred due to steric restraints in [Sb]. Other less efficient methods for silyl removal

include boron trifluoride etherate in potassium," hydrofluoric acid in acet~nitrile.~ We

resorted to TMAF tetrahydrate since effective fluoridation was accomplished with

minimal side reactions? TBDMS was easily rernoved using fluotide ion by fluoride

nucleophilic addition on silicon.

Figure 3.2 shows the direct thiolation of hydroxyl in [5bl to form sulfhydryl in [6] with

Lawesson's reagent (LR). LR or (2.4-bis-(4-methoxypheny1)- l,3,2,4dithiadiphos-

phetane-2,4-disulfide) converts hydroxyl directly to sulfhydryl. The mechanisrn for the

direct thiolation postulates an O-alkylphosphonodithioic acid intermediate."

Nucleophilic addition of [Sb] on LR forms the intermediate. Subsequent P-SH

nucleophilic addition follows by cleavage to form [6]. We considered other methods for

thiolation. However, these methods involve multiple and complex synthetic steps.

1) acid hydrolysis of Bunte salts2' (S-alkyl thiosulfates to foxm thiols),

2) acid hydrolysis of aceta12' (to fom thioacetai and then thiol),

3) acid hydrolysis (peroxyformic acid) of hydroxypheny130 (to form thiols).

Chernical ionization (CI) methods wen used to analyze [Il to [4a] and [4b] and fast-atom

bombardment (FAB) methods were used to analyze [Sb] and [6]. 'H NMR spectra

assignments are given in tenns of chernical shifts. Most elemental analyses erron are

greater than the f 0.4 % acceptable range for carbon and hydrogen probably due to

impurities. These data include values for [l], [2b], [3] and [6].

Figure 3.2: Schematic - NDPEPD direct thiolation

3.3.2 Cornparison - NDPEPD versus ODMAPS

NDPEPD has 3 phenyl units and 2 ethynyl units (see Figure 3.2). Dialkylarnino is the

donor and nitro is the acceptor. ODMAPS has I phenyl, 1 pyridyl and 1 ethenyl unit (see

Figure 3.3). Dialkylarnino is the donor and pyridinium is the acceptor. Both NDPEPD

and ODMAPS have extended conjugation that increases linear and nonlinear

polarizability. Nonlinear poluizability increases by specific donor-acceptor

combinations. Marder er al?' descrîbed donor-acceptor influences on the Is'order

molecular hyperpolarizability, p.

Projecting pont0 the z-axis with the dipole moment, p, results in large nonlinear i2', as

shown by

i 2 j = (kem [ 151

where collinearity is important for and k. NDPEPD is molecularly linear and rigid

with ,u and pdirected dong the z-axis (set Figure 3.3). Therefore, the largest f l component (m ont0 pz allows for charge transfer to fom the excited state on the z-axis.

Figure 3.3: NDPEPD ground and excited (rr-x*) States

Optimal poling of the dipole moment, p, produces optimal 2''. Donor and acceptor

rernain conjugated by pz-electron orbital interactions even during unrestrîcted phenyl

rotation in tolanes?* Banoukas et al." obsewed that tolanes still exhibit peven after 90"

rotations about the z-axis plane. Stilbazoles do not exhibit #Mer z-ais plane rotations

since the px-electron conjugation is broken. Unrestricted phen y 1 rotation in tolanes

contrasts with the restncted phenyl rotation in stilbazoles.

ODMAPS is molecuIarly rigid with p and Pdirected along the z-axis as well (see Figure

3.4). A along allows for charge transfer to occur and form the excited state along the

Figure 3.4: ODMAPS ground and excited (x-x*) States

As mentioned previously, the structural conformation (E)- or trans- from ethenyl nstricts

phenyl rotation in ODMAPS. Stilbazoles have inherently larger f l than tolanes even with

identical donors and acceptors (see Tables 3.2 and 3.3). Both s tilbazole and stilbene have

large and i2', and these are 40-50 % larger than those of tolane. Cheng et al."

attnbuted lower to sp2-hybridized phenyl and sp-hybridized ethynyl interactions (see

Figure 3.5). Diminished electron transfer in ethynyl compared with ethenyl accounts for

large differences in rr-electron energy leveis.

NDPEPD carbon sp2- sp hybridized orbitals

ODMAPS carbon SC- sp2

hybridized orbitals

Figure 3.5: NDPEPD and ODMAPS orbital configurations

However, recent experiments indicated that eth yn y1 significantl y improves opticd

tran~~arenc~.~' In stilbazole derivatives, nonlinearity increases but optical transparency

decreases. A compromise between transparency and nonlinearity must be considered

when optimizing the optical performance. This compromise is known as the nonlinearîty-

transparency trade-off. Marder et aLM demonstrated improvements in both opticd

nonlinearity and transparency in tolanes by increasing the ir-electron conjugation length.

Tables 3.2 and 3.3 show the relationship between Band An, for tolanes and stilbazoles.

In Table 3.2, CN is an acceptor with increasing donor strength from CH30 to N(CH3)2.

With NO2 as an acceptor, the acceptor strength increases as shown Sy die increasing

and p. Donor strength increases as the carbon number of the alkylamino group is

lengthened. Increases in carbon number promotes alkyl tail self-poling and contributes to

p and i2'. In addition, the presence of sulfhydryl appears to increase A- and P substantiall y.

Table 3.1

A- and f l for tolane derivatives (adapted from Marder et

Tolane LU P (Donor : Accepter) (nm) (10 -49 C 3 m/J 3 2 , 10"~esu)

NOTE: All measurements were measured in CHC13. Electric field induced second harmonic (EFISH) measurernents for fl were obtained at 1064 nm.

Table 3.2 A- and f l for stilbazole derivatives

(adapted from Bubeck et al?')

S tilbazole LU f l (Donor : Accepter) (nm) (10 -49 C 3 m 3 /J 2 , 10;" esu)

N=R : N(C3&0H), 354 nm 6.61, 178

CH3-N'=R : N(C16HB)2 475 nm 1 1.2,304

Ch-W-R : N(CiaHnh 325 nm 9.28,250

H - f i R : NCH,(CliH3,) 394 nm -

NOTE: N=R represents pyridinium

In Figure 3.6, the A, for NDPEPD is 455 nm. NDPEPD may be more affected by the

overlapping silver surface plasmon absorbance at 415 nm and may provide a more

effective optical field enhancement than ODMAPS in the MPTMS-silver-MAA-

ODMAPS heterostnicture. Therefore, NDPEPD may overall be a better option than

ODMAPS for use in MPTMS-silver-NLOD heterostructures,

500 6b 700 Wavekngth (nm)

Figure 3.6: UV-VIS spectrum - NDPEPD tolane in methmol

We use NDPEPD and DMAPS (at the bottom of Tables 3.2 and 3.3). In general,

stilbazole has larger ,û than tolam, therefore al1 things king equal, DMAPS should

possess larger 2'' than NDPEPD. Moylan et al? also noted that tolanes (including

NDPEPD) possess lower f l than stilbazoles (including ODMAPS). In our i2' measurements, we simultaneousl y monitor ia responses as poling occurs until maximum

f ' . Table 3.4 compares i2' (1 -5 x 10-23 &J2 or 0.4 x 1 0 ~ CSU) for PS-NDPEPD to those

for other NLODs doped into poly(styrene).

Table 3.3

i2' for NDPEPD and DMAPS in poly(styrene)

NLOD doped into f ' 23 3 2 Poly(stpne) (10- C IJ , lu8 esu)

PS-NDPEPD 1.49,0.40

PS-Disperse Red 1" 4.46, 1.20

PS-DMAPS~~ 2.90,0.78

Differences between 2'' for PS-NDPEPD and PS-DMAPS result from lower ,ûof

NDPEPD. as discussed previously. Overall, the i2' for PS-NDPEPD is comparable io

many similar organic NLODs and may prove to be better in the nonlinearity-transparency

trade-off regime.2g

Conclusions

summnry

We successfully synthesized an alternative NLOD tolane (NDPEPD) that possesses

spacers that can be chemisorbed direcily ont0 silver or gold nanoparticle surfaces without

the requirement of an additional separate spacer. Palladium-catalyzed cross-coupling of

IPD and NEDPA provided access to design the linear NDPEPD. Direct thiolation with

Lawesson's reagent was used to convert hydroxyl directly to suuhydryl. Thiolation was

not performed prior to cross-coupling due to inevitable contamination of the palladium

catal yst. Desilanation of TBDMS with TMAF proved to be more effective than

deacetylation with potassium carbonate and sodium hydroxide in rernoving protecting

groups on [4b] and [4a], respectively.

23 3 2 i2' for PS-NDPEPD (1.5 x 1U C /J or 0.4 x 10" esu) compared favorably to those

PS-DMAPS (2.90 x 10'~ or 0.78 x 10-~ esu). In both cases, the AC2' of the organic

NDPEPD and DMAPS were comparable those of the organic NLODs listed. Potentiai for

effective silver surface plasmon optical field enhancements were evident with the use of

NDPEPD, which has A- at 455 nm. Therefore, NDPEPD demonstrates itself as a

cornpetitive NLOD alternative to potentially replace ODMAPS in the MPTMS-silver-

MAA-ODMAPS heterostructure.

Future Research

We suggest further exploration of design strategies for advancing NDPEPD tolane

synthesis. P'lWP cataiyst contamination may be eliminated by starting with extrernely

pure IPD and NEDPA. Improvernents in #3 while maintaining transparency may be

incorporated into NDPEPD for uses in optical device applications. NDPEPD may also be

anchored into polyrner to prevent relaxation decay after electrical field poling, thereby

alleviating i2' decay in PS-NDPEPD composites.

References

' (a) H. W. Fox, E. F. Hase, W. A. Zisman, J. Colloid Sei. 8, 194 ( 1953); (b) A. Aviram,

M. A. Ratner, Chem Phys. Lett. 29,277 (1974); (c) A. -A. Dhirani, R. W. Zehner, R. P.

Hsung, P. Guyot-Sionnest, L. R. Sita, J. Am. Chem. Soc. 118.33 19-3320 (1996).

G. J. Ashwell, P. D. Jackson, G. Jefferies, 1. R. Gentle, C. H. L. Kennard, J. Mater.

Chem. 6,2, 131-136 (1996).

J. P. Gao and G. D. Darling, J. Am. Chem. Soc. 114,3997-3998 (1992).

' (a) L.-T. Cheng, W. Tm, G. R. Meredith, G. L. J. A. Rikken, E. W. Meijer, SPIE

Proc. 1147,61-72 (1989); (b) L.-T. Cheng, W. Tarn. S. H. Stevenson, G. R. Meredith,

G. Rikken, S. R. Marder, J. Phys. Chem. 95, 1063 1-10643 (1991); (c) L. -T. Cheng, W.

Tarn, S. R. Marder, A. E. Steigman, G. Rikken, C. W. Spangler, J. Phys. Chem. 95,

10643-10652 (1991).

* R. Q. Brewster, Organic Synthesis Collection - Vol. II, A. H. Blatt, Ed., Wiley, New

York, 1943, pp. 347-349.

G. Hofle, W. Steglich. H. Vorbrliggen, Angew. Chem. [nt. Ed. Engl. 17,569 (1978).

' E. J. Corey, B. B. Snider, J. Am. Chem. Soc. 94,2549 (1972).

P. Nguyen, G. Lesley, T. B. Marder, Chem Marer. 9.406-408 (1997).

1. I. Plattner, R. D. Gless, H. Rapoport, J. Am. Chem Soc. 94,86 13 (1972).

'O B. W. Metcalf, J. P. Burichart and K. Jund, Tetrnhed. Leu., 21,35-36 (1980).

I L T. Nishio, J. Chem. Soc. Perkîn Trans. 1, 1 1 13-1 1 17 ( 1993).

" F. F. Heck, Palladium Reagents in Organic Synthesis, Acadernic Press. London, 1985.

l 3 A. Schonberg,, M. Z . Barakat. J. Chem. Soc. 892 (1949).

I4 G. J. Shugar, R. A. Shugar, L. Bauman, R. Shugar Bauman, Chernical Technician's

Ready Reference Handbook, Edition, McGraw-Hill. New York, 198 1, pp. 63.

l5 (a) M. A. Mortazavi, A. Knoesen, S. T. Kowel, B. G. Higgins, A. Dienes, J. Opt. Soc.

Am. B 6,4 (1989); (b) K. D. Singer, J. E. Sohn. S. J. Lalama, Appl. Phys. Lett. 49.

248-250 (1986); (c) G. R. Meredith, J. G. van Duser, D. J. Williams, Macromolecules

5, 1385-1389 (1982); (ci) P. Pantelis, J. R. Hill. G. J. Davies, in Nonlinear Optical and

Elecrroactive Poljmers, P. N. Prasad, D. R Ulrich, Eds., Plenum h s s , New York,

1988, pp. 119.

0 l6 K. K. Olgivie, S. L. Beaucage, A. L. Schifman, N. Y. Theriault, K. L. Sadana, Con. J. Chem. 56,2768 (1978).

17 H. Weber, H. G. Khorana, J. Mol. Biol. 72,219 (1972).

S. K. Chaudhary, O. Hernandez, Tetrahed Lea. 99 (1979).

l9 E. J. Corey and A. Venkateswarlu, ' Amer. Chem. Soc. 94,6 190 (1972).

G. A. Olah, B. G. B. Gupta, S. C. Narang, R. Mdhotra, J. Org. Chem. 44,4272 (1979).

" P. Nguyen, 2. Yuan, L. Agocs, G. Lesley and T. B. Marder, Inorg. Chim. Acta 220,

289-296 (1 994).

" (a) S. Takahashi, Y, Yuroyama, K. Sonogashira and N. Hagihara, Synrhesis 627

(1980); (b) W. B. Austin, N. Bilow, W. J. Kelleghan and S. Y. Lau, J. Org. Chem. 46,

2280 (1981); (c) E. T. Sabourin and A. Onopchenko, J. Org. Chem. 48,5135 (1983);

( d ) L. D. Ciana and A. Haim, J. Heterocycl. Chem. 21,607 ( 1984); (e) S. J. Havens

and P. M. Hergenrother, J. Org. Chem. 50, 1763 (1985); ( f ) T. X. Neenan and G. M.

Whitesides, J. Org. Chem. 53,2489 (1988); (g) R. Singh and G. Just, J. Org. Chem.

54,4453 (1989); (h) M. A. De la Rosa, E. Velarde and A. Guzman, Synth. Commun.

20,2059 (1990); (i) D. Villemin and E. Schigeko, J. Organomet. Chem. 293, C 10

(1985); 0') K. A. Hom, R. B. Grossman and A. A. Whitenack, J. Orgonomet. Chem.

332,27 1 (1987).

23 K. Mori, M. Tomenaga, T. Takigawa, M. Matsui, Synthesis 790 (1973).

24 L. A. Carpino, A. C. Sau, J. Chem. Soc. Chem. Commun. 5 14 (1979).

R. F. Newton, D. P. Reynolds, M. A. W. Finch, D. R. Kelly, S . M . Roberts, Tetrah.

Lm. 398 1 (1979).

26 B. C. Ahvazi, D. S. Argyropoulos, J. Agr. Food Chem 44,2 167-2 175 ( 1996).

27 T. Nishio, J. Chem Soc. Perkin. Trms. 1 11 13 (1993).

T. S. Price, D. F. Twiss, J. Chem. Soc. 95, 1725 (1909).

" (a) M. d'Alarcao and N. J. Leonard, J. Am Chem. Soc. 105,5958 (1983); (b) K.

Mikami, K.4. Anima and T. Nakai, Tetrohedron 40,2308 (1 984); (c) A. N. Tischler

and T. J. Lanza, Tetrahed. Lett. 27, 1653 (1986); (d) B. M Trost, C. Chan and G.

Ruhter, J. Arn. Chem. Soc. 109,3486 (1987); (e) Y. Zhang and J. Wen, Synthesis 727

(1990).

30 (a) W. B. Austin, N. Bilow, W. I. Weghan and S. Y. Lau, 3. Org. Chem. 46,2280

e (198 1); (b) E. T. Sabourin and A. ûnopchenko, J. Org. Chem. 48,5 135 (1983);

(c) L. D. Ciana and A. Haim, J. Heterocycl. Chem. 21,607 (1984); (d) S. I. Havens

and P. M. Hergenrother, J. Org. Chem. 50,1763 (1 985); (e) T. X. Neenan and G. M.

Whitesides, J. Org. Chem. 53,2489 (1988); (f) R Singh and G. Just, J. Org. Chem.

54,4453 (1989); (g) M. A. De la Rosa, E. Velarde and A. Guanan, Synth. Commun.

20,2059 (1990); (h) D. Villemin and E. Schigeko, J. Organornet. Chem. 293, Cl0

(1 985); (i) K. A. Hom, R. B. Grossman and A. A. Whitenack, J. Organomet. Chem.

332,271 (1987).

" (a) J. W. Perry, A. E. Stiegman, S. R. Marder, D. R Coulter, D. N. Beratan, D. E.

Brinza, F. L. Klavetter, R. H . Gnibbs, SPIE Proc. 971, 17 (1988); (b) J. W. Perry, A.

E. Stiegman, S. R. Marder, D. R. Coulter, D. N. Beratan, D. E. Brinza, F. L. Klavetter,

R. H. Gnibbs, SPIE Proc. 971,17 (1988); (c) W. Tarn, Y. Wang, I. C. Calabrese, R. A.

Clement, SPIE Proc. 971, 107 (1988); (d) Y. Wang, W. T m , S. H. Stevenson, R. A.

Clement, J. Calabrese, Chem. Phys. Lett. 148, 136 ( 1 988).

'* D. Ingle, S. R Crouch, Spectrochenticul Ana&sis, Prentice Hall, Englewood Cliffs, NI,

1988, pp. 317.

33 M. Barzoukas, A. Fort, G. Klein, A. Boeglin, C. Serbutoviez, L. Oswald, 5. F. Nicoud,

Chem. Phys. 153,457 (1991).

34 L. -T. Cheng, W. Tarn, S. R. Marder, A. E. Stiegeman, G. Rikken, C. W. Spangler, A

Phys. Chem. 95,10643 (1991).

'' A. E. Stiegman, V. M. Miskowski, J. W. Peny, D. R. Coulter, J. Am. Chem. Soc. 109,

5884 (1987).

36 S. M. Lovejoy, S. Emer, D. S. Leung, C. W. Dirk, P. Kalmegham, L. Zhang, C. R.

Moy lan, in Organic Th in F i h for Photonia App[icutions - Technical Digest, Vo 1.

" C. Bubeck, A. Laschewsky, D. Lupo, D. Neher, P. Ottentreit, W. Paulus, W. Prass, H.

Ringsdorf, G. Wegner, Advanced Mater. 3,54 ( 1 9%).

38 C.R. Moylan, C. A, Walsh, Nonlhear Optics 6,113-1 21 (1993).

39 T. J. Marks, M. A. Ratner, Angew. Chem. Int. Ed. Engl. 34, 155-173, (1995).

Appendix

Units Conversion Table A-1 lis& cornmon units used in nonlinear optics for MKS, SI (système

international) and esu (electrostatic unit) systems. Units for i2' follows from the MKS

system, as used in the literature. Q defines the conversion factor, and N is the physical

quantity of interest.

Table A- 1

Units for polarizability, hyperpolarizability and nonlinear susceptibility

Ph ysicai MKS SI esu* NsiQ = Na" NMKSQ = N a Quantity A

Units described by the esu* system are often quoted as esu units.

Note:

C = coulomb

SC = statcoulomb (also represents esu units)

J =joule

m = meter

pm = picorneter

V = volt

Units Conversion

Table A- 1 lists common units used in nonlinear optics for MKS, SI (système

international) and esu (electrostatic unit) systerns. Units for 2" follows frorn the MKS

system, as used in the Iiteratun. Q defines the conversion factor. and N is the physical

quantity of interest.

Table A- 1

Units for polarizability, hyperpolarizability and nonlinear susceptibility

Uni& descnbed by the esu* system are often quoted as esu units.

Note:

C = coulomb

SC = statcoulomb (also rcpmnts esu units)

J = joule

m = meter

pm = picorneter

V = volt