Marina Freitag

Advisor: Prof. Elena Galoppini

Rutgers University – Newark

Ph.D. defense presented on: Sep 28th 2011

Outline

2

1. Introduction

1. Nanostructured Metal Oxide Interfaces

2. Background

3. The Cucurbituril Family

4. Inclusion of Methylviologen in Cucurbit[7]uril

2. Electrochromic properties of Viologen Cucurbituril complexes

1. Redox Active Compounds on TiO2

2. Viologens and their Synthesis

3. Host-guest Complexes

4. Electrochromic Devices

5. Characterization

6. Conclusions

3. Fluorescence properties of Tolyl-Viologen derivatives

1. Introduction

2. Viologen derivative synthesis

3. NMR titration

4. Emission titration

5. Quantum yield

6. Lifetime

7. Characterization

8. Conclusions

Metal Oxide Nanoparticles

3

Differences in the bandgap

between metals, semiconductors

(metal oxides) and insulators

Synthesis, characterization, and modification of nanoparticles and nanostructures

• Alternative method to attach molecules to semiconductors

• Shield the guest from the heterogeneous interface

• Lead to new chemical, photophysical and electrochemical properties 4

Surface Functionalization Methods

physisorption

trapping in

cavities covalent binding

For LED, solar cell and sensors

applications, nanoparticle

functionalization is necessary

Cathode (Au)

Electrolyte

TiO2 layer

Anode (FTO)

Glass

DSSC

The Hosts

5

U. H. Brinker, J.-L. Mieusset, Molecular Encapsulation: Organic Reactions in Constrained Systems, John Wiley and

Sons, 2010

M. Freitag , E. Galoppini, Energy & Environmental Science, 2011

e-

e-

Pioneering Work

H. Choi et al., Angew. Chem. Int. Ed., 2009, 48, 1.

P. Piotrowiak et al., Pure Appl. Chem., 2003, 75, 1061

C. Pagba et al., J. Am. Chem. Soc. 2004, 126, 9888.

S. A. Haque et al., Adv. Mater., 2004, 16, 1177.1

• Possible to find matching host

• High complexation constants

• Structural modification of guest with

anchor group is not needed

• Prevents aggregates

• Improves Chemical stability

• Prevents quenching

• Shields guest from semiconductor

surface

6

Cucurbituril Family

7

• Macrocyclic host consisting of glycoluril repeating units

• Particularly high affinity for positively charged compounds

• Commercially available

Cucurbit[7]uril

8

• Solubilization and prevention of

aggregation with CB[7]

• Negative electrostatic potential, leads

to a preference of cationic guests

• Condensation of glycoluril with

formaldehyde

• Changing the temperature of the

reaction to between 750C and 900C

to access other sizes of cucurbiturils

(CBs)

• Fractional dissolution and fractional

crystallization to separate different

cucurbituril homologues

Electrochromism of Viologens

9

• Highly efficient excited-state electron acceptor E°(MV2+*/MV•+) = 3.65 V

• Fast photoreduction (< 250 fs)

• Reversible color change

H. J. Kim, W. S. Jeon, Y. H. Ko and K. Kim, Proc. Natl. Acad. Sci. U. S. A., 2002, 99, 5007.

K. Kim, N. Selvapalam, Y. H. Ko, K. M. Park, D. Kim, K. J. Kim, Chem. Soc. Rev., 2007, 36, 267.

Viologen@CB[7] Complexes

10 Kim, K. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 5007

• Thermodynamically and kinetically stable

complexes in aqueous solutions

• Reversible electrochemical behavior in

solution

• Ion-dipole interaction between positively

charged guests and carbonyl oxygen's at the

portals of CB[7]

Outline

11

1. Introduction

1. Nanostructured Metal Oxide Interfaces

2. Background

3. The Cucurbituril Family

4. Inclusion of Methylviologen in Cucurbit[7]uril

2. Electrochromic properties of Viologen Cucurbituril complexes

1. Redox Active Compounds on TiO2

2. Viologens and their Synthesis

3. Host-guest Complexes

4. Electrochromic Devices

5. Characterization

6. Conclusions

3. Fluorescence properties of Tolyl-Viologen derivatives

1. Introduction

2. Viologen derivative synthesis

3. NMR titration

4. Emission titration

5. Quantum yield

6. Lifetime

7. Characterization

8. Conclusions

Alkyl Viologen Derivatives Bound to MOn

12

• Use of anchoring groups for binding on TiO2

• Electrolyte: LiClO4, Ferrocene, γ-Butyrolactone

• Problems and side effects: dimerization,

insolubility of the neutral species

Cummins, D., Boschloo, G., Ryan, M., Corr, D., Rao, S. N.Fitzmaurice, D. J. Phys. Chem. B, 2000, 104, 1144

1 V

Guests: Viologens

13

Alkyl Viologen Synthesis

14 Cummins, D., Boschloo, G., Ryan, M., Corr, D., Rao, S. N.Fitzmaurice, D. J. Phys. Chem. B, 2000, 104, 1144

Synthesis of phosphonated viologen (4) and carboxylated viologen (5) by

Menshutkin reaction

Aryl Viologen Synthesis MTV2+

15

MTV2+ (2) was synthesized as shown, using an adaptation of the Zincke reaction

by Yamaguchi and coworkers to obtain asymmetric viologen derivatives.

Yamaguchi, I., Higashi, H., Shigesue, S., and Shingai, S. Tetrahedron Lett. 2007, 48, 7778

Zincke, T. H. and Weisspfenning, G. J. Liebigs Ann. Chem. 1913, 396, 103

Cucurbituril complexes bound to MOn

• Role of Cucurbituril: prevention of side

reactions and as binding unit to TiO2

• Binding from aqueous solution

• Inclusion confirmed by 1H NMR in

solution and UV-VIS of electrochromic

windows

16

FTO-TiO2

Complexation Constant for MTV2+

17

Benesi-Hildebrand method

NMR Complexation

18

NMR Complexation

19

Complexation and Binding

20

MOn blank Viologen@CB[7]/MOn

Binding

24h

MOn preparation:

sol-gel technique

TiO2/ ZrO2

Chemisorption (or physisorption) of MV2+@CB[7] or MTV2+@CB[7] was done by

immersing the films in an aqueous solution with the complex (0.5 mM) for 24 h.

• Equimolar amounts of MV2+ (or MTV2+) and CB[7] were dissolved in distilled

water (100 mL) to form the guest@host complex and stirred overnight.

• Formation of the complexes in solution was monitored by 1HNMR in D2O.

• It was observed that the complexation is fast (minutes).

Construction of ECW

21

Vinyl mask FTO substrate TiO2 film Binding of the complex

Counter electrode

Assembly with

thermoplastic

Surlyn

Final device

Cyclic Voltammetry in Solution

22

CV in 0.1 M phosphate buffer

(pH 7.0) of 0.05 mM solutions Compound

E11/2,V

(ΔEp, mV

vs Ag/AgCl)

E21/2, V

(ΔEp, mV

vs Ag/AgCl)

MV2+

-0.661 -0.975

MV2+

@CB[7 -0.681 -0.992

MTV2+

-0.704

MTV2+

@CB[7 -0.767

Cyclic Voltammetry of ECW

23

• The CVs of electrochromic windows prepared from MV2+@CB[7] and

MTV2+@CB[7]

• Both complexes show a semi-reversible two-electron reduction process

• The complex formation and the physisorption to TiO2 are necessary to

bring the unsubstituted viologens close to the semiconductor surface

• Control experiment: free Methylviologen shows no binding to MOn

MV2+ @CB[7] ECW

MTV2+ @CB[7] ECW

Absorption Spectra in Solution

24

• One-electron-reduced species were measured in solution at -0.6 V in the

presence and absence of one equivalent of CB[7]

• Broad absorption band centered at 600 nm

200 300 400 500

0.0

0.2

0.4

0.6

0.8

1.0

MV2+

MV2+

@CB[7]

Ab

so

rba

nce

a.u

.

Wavelength [nm]

Dication Radical Cation

500 600 700 800

0.00

0.25

0.50

0.75

1.00

Ab

so

rba

nce

a.u

.

Wavelength [nm]

MV.+

MV.+

@CB[7]

Absorption Spectra in Solution

• The spectra of the complexes were essentially identical to those of the

free compounds. 25

200 300 400 500

0.0

0.2

0.4

0.6

0.8

1.0

MTV2+

MTV2+

@CB[7]

Ab

so

rba

nce

a.u

.

Wavelength [nm]

Dication Radical Cation

500 600 700 800

0.00

0.25

0.50

0.75

1.00

Ab

so

rba

nce

a.u

.

Wavelength [nm]

MTV.+

MTV.+

@CB[7]

Absorption Spectra of ECW Colored State

• Absorption spectra of MV2+@CB[7]/TiO2 andMTV2+@CB[7]/TiO2 measured in an

electrochromic window after application of -0.6 V

• Broad band around 600 nm

• Consistent with the absorption spectrum of the corresponding radical cations

• Coloration was reversible for over 20 switching cycles between bleached and

colored state 26

Conclusions

27

• Complexes of methylviologen (MV2+) and 1-methyl-1’-p-tolyl-4,4’-

bipyridinium dichloride (MTV2+) were encapsulated in a molecular host, CB[7],

and physisorbed onto the surface of TiO2 nanoparticle films

• Proof-of-concept demonstrated the electrochromic properties of two viologen

guests encapsulated inside a cucur[7]bituril host where the host was bound

to the surface of the semiconductor

• No need for synthetic modifications of the molecules with binding groups

• Electrochromic windows were prepared using viologen@CB[7]-modified TiO2

films cast on FTO electrodes.

• These windows exhibited reversible color switching upon application of -0.8

V, corresponding to the formation of intensely blue radical cations

Outline

28

1. Introduction

1. Nanostructured Metal Oxide Interfaces

2. Background

3. The Cucurbituril Family

4. Inclusion of Methylviologen in Cucurbit[7]uril

2. Electrochromic properties of Viologen Cucurbituril complexes

1. Redox Active Compounds on TiO2

2. Viologens and their Synthesis

3. Host-guest Complexes

4. Electrochromic Devices

5. Characterization

6. Conclusions

3. Fluorescence properties of Tolyl-Viologen derivatives

1. Introduction

2. Viologen derivative synthesis

3. NMR titration

4. Emission titration

5. Quantum yield

6. Lifetime

7. Characterization

8. Conclusions

Fluorescence Properties Tolyl-Viologen in CB[7]

29

Cucurbituril Encapsulation of Fluorescent Dyes

30

Marquez, C.; Huang, F.; Nau, W. M. IEEE Trans.

NanoBiosci. 2004, 3, 39.

A. Hennig, M. Florea, D. Roth, T. Enderle, W. M. Nau,

Supramolecular Chemistry, 2007 (19) 55–66

• Increase of quantum yield

• Longer lifetimes

• Enhanced photostability

• Protected towards quenchers

• Prevents disaggregation

• Solubilization

• Change in absorption and emission

properties

31

The Viologens

p. 211

Fluorescent

OXO-Bipyridilium

Compounds

A.W.-H. Mau, J.M. Overbeek, J.W. Loder, W.H.F. Sasse, J. Chem. Soc., Faraday Trans. 2, 1986,82, 869.

BUT…

The fluorescence and excited state properties of MV2+ were thoroughly

characterized for the first time by Kohler and coworkers a decade ago.

“For example, MV2+ will quench the fluorescence of species

such as excited state [Ru(bipy)3] 2+.

A few workers have claimed that methyl viologen dication will

fluoresce, although it is now considered that much of the

‘fluorescence’ reported is in fact due to minute traces of

highly fluorescenig ’oxo’-viologen compounds as impurities.”

Host and Guests

32

Synthesis

33

12

14

Viologen region

1H NMR Titration of DTV2+ (1µM) with CB[7]

In 0.05 M NaCl / D2O

In D2O

1H NMR Titration

34

Binding Modes within the Host Cavity

35

Stoichiometry - Host - Guest

36

1:2

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

in 0.05M NaCl

in water

DTV2+

with CB[7]

Inte

gra

ted

Flu

ore

sce

nce

In

ten

sity a

.u.

CB[7]/[DTV2+

]

1:1 1:2

0.0 0.2 0.4 0.6 0.8 1.0

0

10000

20000

30000

40000

50000

60000

70000 in Water

in 0.05 M NaCl

Inte

gra

ted

Flu

ore

se

nce

In

ten

sity a

.u.

nDTV

2+/(nDTV

2++nCB[7]

)

0.33

Job's Plot

37

250 300 350 400 450 500 550 600 650

0.0

0.2

0.4

0.6

0.8

1.0

1.2

em

=470 nm

No

rma

lize

d In

ten

sity a

.u.

Wavelength [nm]

DTV2+

@CB[7] Absorption

DTV2+

@CB[7] Emission

max

=335 nm

135 nm

400 450 500 550 600 650

0

50

100

150

200

250

300

350

400

450

ex

= 350 nm

FL

= 470 nm

Em

issio

n a

.u.

Wavelength [nm]

1M DTV2+

em

= 505 nm

MCB[7]

Emission Properties of the Complex

Quantum Yield

44

Lakowicz, J. R. Principles of Fluorescence Spectroscopy,1999, Kluwer Academic / Plenum Publishers *

ex [nm] FL [nm]

DTV2+ 350 505 0.02 < 20 ps

DTV2+@CB[7]

1:1

350 482 0.12 0.4 ns

DTV2+@CB[7]

1:2

350 470 0.29 0.65 ns

DTV2+@CB[7]

1:3

350 470 0.28 0.70 ns

Tryptophan* 300 355 0.14

Conformation Effect

39

400 450 500 550 600

0

20

40

60

80

100

120

140

Em

issio

n a

.u.

Wavelength [nm]

DTV2+

in PMMA

PMMA

em= 465 nm

ex

= 350 nm

Emission spectra of DTV2+ in polymer matrix of PMMA

• Structural factors (delocalized π-electrons, electron donating groups,

chelation effect, pH etc )

• Quenching

PMMA

DFT and CIS Calculations

40

• S0, S1 and T1 states of DTV2+

• Indicating the inter-ring dihedral angles

• The (S0-S1) and (S1-T1) and

intramolecular reorganization energies

• The three semi planar rings exhibit

alternating bond lengths.

• Bonds with length changing by more

than 0.025 Å, contraction in red and

lengthening in green

300 400 500 600

0.0

0.5

1.0

1.5

DTV.+

Ab

so

rba

nce

a.u

.

Wavelength [nm]

DTV2+

330 nm 400 nm

300 400 500 600

0.0

0.5

1.0

1.5

Ab

so

rba

nce

a.u

.

Wavelength [nm]

DTV2+

DTV.+

335 nm 400 nm

Electrochromic Properties

41

UV-VIS spectra of DTV2+ @CB[7] in water

before and after reduction

UV-VIS spectra of DTV2+ in water before and

after reduction

• Viologen was reduced electrochemically by applying -1.0 V

and chemically with 1M NaOH in Methanol

Electrochromic Properties

42

400 450 500 550 600 650

0

5

10

15

20

25

ex

=350 nm

Inte

nsity a

.u.

Wavelength [nm]

DTV.+

DTV2+

em

=527 nm

400 450 500 550 600 650

0

100

200

300

400

500

600

DTV.+

ex

=350 nm

Inte

nsity a

.u.

Wavelength [nm]

DTV2+

em

=475 nm

Emission spectra of DTV2+ @CB[7] in water

before and after reduction

Emission spectra of DTV2+ in water before and

after reduction

• Viologen was reduced electrochemically by applying a

voltage of -1.0 V and chemically with 1M NaOH in Methanol

Complex on Metal Oxide Surface

43

400 450 500 550 600

0

1

2

3

4

5

6

7

8

ex

= 350 nm

Em

issio

n a

.u.

Wavelength [nm]

DTV2+

@CB[7] on ZrO2

em= 480 nm

•Fluorescence spectra of the

DTV2+@CB[7] bound to ZrO2

•ZrO2 is an insulator, similar

morphology to the semiconductor

TiO2

Conclusions

44

Use of Cucurbituril as a Host

• Encapsulation of fluorescent dyes in Cucurbituril can lead to numerous

applications

• Benefits of encapsulation: solubilization, deaggregation, photostabillization

• Pronounced enhancement of fluorescence

• Prolonged lifetime

• Restriction of conformational changes

• Binding unit to the metal oxide nanoparticles

New Viologen Derivative DTV2+

• First viologen derivative showing fluorescent properties

• DFT calculations confirm conformational effect

• Position of Methyl group in benzylic positions is key component

• Restriction of molecular mobility is necessary to enhance fluorescence (CB[7]

or Polymer matrix)

Acknowledgements

Advisor: Prof. Elena Galoppini

Thesis committee: Prof. Phillip Huskey of Rutgers University, Newark

Prof. Jenny Lockard of Rutgers University, Newark

Prof. Angel E. Kaifer of University of Miami, Florida

Collaborators: Prof. Piotr Piotrowiak, Prof. Lars Gundlach – Laser measurements

Prof. Carlo Bignozzi, Dr. Stefano Caramori – Research visit 2009

Prof. Richard Mendelsohn, Dr. Carol Flach – FT-IR-ATR Instrument

Research group: Prof. Jonathan Rochford, Prof. Olena Taratula, Dr. Sujatha Thyagarajan,

Dr. Yongyi Zhang, Andrew Kopecky, Keyur Chitre, Yan Cao

and Agnieszka Klimczak

Chemistry dept.: Prof. Philip W. Huskey, Prof. Frank Jordan and Prof. John Sheridan and all

professors and staff, former and current members of Rutgers Chemistry

Department Newark and especially to Judy Slocum, Monika Dabrowski

Lorraine McClendon, Paulo Vares and Maria Araujo

Financial support: Donors of the American Chemical Society Petroleum Research Fund

(ACS PRF #46663-AC10).

45

Thank you!

47