The photophysical properties of quadruply bonded M2 arylethynyl carboxylate complexes

64th International Symposium on Molecular Spectroscopy

Carly Reed 6.22.09

Quadruply Bonded Dimetal Units

Conjugated organic polymers potential applications: thin-film transistors, organic solar cells, and molecular memory devices.

Incorporating quadruply bonded dimetal units into conjugated organic polymers is of interest to determine new tunable optoelectronic properties.

M2 M2 M2M2 M2 M2

M2 M2M2 M2 M2M2

M = Mo, W

Macromol. Chem. Phys. 2008, 209, 1319

TiPB

TiPB

Dimetal units are brought into conjugation with conjugated ligand by carboxylate tethers

Key orbital interactions involve M2 and CO2 combinations with the system of the conjugated ligand

Out of phase combination of * mixes strongly with M2 orbitals However in-phase has no symmetry match

TiPB =

PNAS, 2008, 105 (40), 15247

Absorption, - - - Excitation, Emission (r.t.), …. Emission (77K)

J. Am. Chem. Soc. 2005, 127, 17343-17352

4b

Background

Observed short lived visible emission originating from 1MLCT (Mo2 )1 (O2C-aryl *)

Visible emission decayed < 10 ns, however, in ns-TA a long lived excited state was observed (s)

Tentatively assigned as 3MLCT non-emissive excited state

Motivation

What is the nature and behavior of this long lived excited state; how can it be tuned? Can steric interactions be alleviated while maintaining conjugation? How will this effect the excited

state charge distribution?

Steric interactions between carboxylate oxygen and peri-H atoms on anthracene cause twisting of conjugated ligand out dimetal plane in complex shown to have longest lived excited state (76 s).

J. Am. Chem. Soc. 2006, 128, 6776-6777. The Chemical Record. 2005, 5, 308-

320.

Dihedral = ~45o (oblique), ~85o (perpendicular)

O

OH

O

OH

Solution: Introduce ethynyl unit

Mo

Mo O

O

O

O

O

O

O

OMo

Mo O

O

O

O

O

O

O

O

W

W O

O

O

O

O

O

O

O

W

W O

O

O

O

O

O

O

O

1 2

3 4

/ nm

200 300 400 500 600 700 800

Osc

illa

tor

Str

eng

th C

alcu

late

d T

ran

siti

on

s

0

1

2

3

4

5

6

Calculated TransitionsAbsorbance

/ nm

200 300 400 500 600 700

Cal

cula

ted

Osc

illat

or

Str

eng

th

0.0

0.5

1.0

1.5

2.0

2.5

3.0

DFT-Calculations

574 nm: MO 164 (HOMO) 165 (LUMO)426 nm: MO 162 165362 nm: MO 164 168

DFT calculations utilized B3LYP functionalbasis set 6-31G* for non-metal atoms and SDD energy consistent pseudo-potential for Mo

461 nm: MO 120 (HOMO) 121 (LUMO) 284 nm: MO 118 121

120

121

125

116

117

122

132

120

121

125

116

117

122

132

533 nm: 120 (HOMO) 121 (LUMO)

344 nm: 120 125297 nm: 116 121 117 122 120 132

677 nm: 164 (HOMO) 165 (LUMO) 443 nm: 162 165; 164 168 349 nm: 164 171 320nm: 159 165; 164 172

172

171

168

165

164

162

159

172

171

168

165

164

162

159

DFT-Calculations

DFT calculations utilized B3LYP functionalbasis set 6-31G* for non-metal atoms and SDD energy consistent pseudo-potential for Mo

max = 570 nm, ~710 nm; THF

Emissive Properties of Molybdenum Complexes

Solvent Dependence NIR emission

1 em 2 em

THF 1072 nm/ 9,328 cm-1 1080 nm/ 9,259 cm-1

CH2Cl2 1060 nm / 9,433 cm-1 1075 nm/ 9302 cm-1

MeCN 1065 nm / 9,389 cm-1

Vibronic spacing 300-420 cm-1.

Indicative of M-M symmetric stretching frequencies.

Time delay (s)

0 5e-5 1e-4 1e-4 2e-4

O

D

-0.005

0.000

0.005

0.010

0.015

0.020

0.025

0.030

decay at 450 nm

= 103 s

time (s)

0 5e-5 1e-4 1e-4 2e-4

OD

-0.005

0.000

0.005

0.010

0.015

0.020

0.025

0.030

decay at 420 nm

fs-TA ns-TA

Mo2(TiPB)2(O2CC2C6H4CH3)2 4.7 ps 103s

Mo2(TiPB)2(O2CC2C14H9)2 86 s

= 86 s

Nd:YAG laser (fwhm ~ 8ns, ~ 5 mJ per pulse

Long-lived triplet excited state on microsecond time-scale also indicates MM* excited state, matching well with Mo2TIPB4 long-lived excited state (43 s)

Inorg. Chem. 2009, 48, 4394

ns-Transient Absorption

SOMO 1

SOMO 2

LUMO

Molden plots of frontier orbitals plots showing the character of the lowest energy triplet state, T1, for each complex.

Mo2(TiPB)2(Tolyl)2 Mo2(TiPB)2(Anthryl)2

DFT calculations utilized unrestricted B3LYP (UB3LYP) functionalbasis set 6-31G* for non-metal atoms and SDD energy consistent pseudo-potential for Mo

DFT Calculations

In molybdenum complexes long lived excited state assigned as 3*

Ligand Independent

Solvent Independence

Vibronic Features

DFT Calculations

Mo

Mo O

O

O

O

O

O

O

O

Mo

Mo O

O

O

O

O

O

O

O

3*

Compounds labs, nm and lem, nm Stokes shift

W2(TiPB)2(O2CC2C6H4CH3)2 610 nm, ~ 670 nm, 875 nm

~1470 cm-1, 4965 cm-1

W2(TiPB)2(O2CC2C14H9)2 760 nm, 830 nm 1109 cm-1

Emissive Properties of Tungsten Complexes

Do not see vibronic features at low temp

W2TiPB4 3* emission 815nmInorg. Chem. 2009, 48, 4394

Nd:YAG laser (fwhm ~ 8ns, ~ 5 mJ per pulse

fs-TA ns-TA

W2(TiPB)2(O2CC2C6H4CH3)2 < 1 ps < 10 ns

W2(TiPB)2(O2CC2C14H9)2 ? < 10 ns

Longest lived excited state indicated lowest energy excited state is something other 3* for these tungsten compounds because W2(TiPB)4 lowest energy long lived excited state existed with = 1.6 s

Inorg. Chem. 2009, 48, 4394

ns - Transient Absorption

Molden plots of frontier orbitals plots showing the character of the lowest energy triplet state, T1, for each complex.

LUMO

SOMO 2

SOMO1

HOMO

In tungsten complexes long lived excited state is not 3*

DFT Calculations

Emission energies differ from W2(TiPB)4 and show no vibronic features

Shorter triplet lifetime compared to W2(TiPB)4 (1.6 s)

W

W O

O

O

O

O

O

O

O

W

W O

O

O

O

O

O

O

O

Future Work Part:

Further explore nature of long-lived excited state with time resolved IR and Raman

Thank You!

Thanks to: Prof. Malcolm Chisholm Prof. Claudia Turro Chisholm Group Members Turro Group Members NSF Wright Center for Photovoltaics Innovation and Commercialization Ohio Supercomputing Center

Br Si(Me)3Si(Me)3

CuI, Pd(PPh3)2(Cl)2, Et3N

Reflux (18hr 110oC)+

1 2

20.40% aq. KOH soln, THF/MeOH (wet) (4:1)

H

3

3 1.0 BuLi+1. THF, -40oC, stir 1 hr, warm to r.t.

2. CO2 (g), 90 min

O

OH

Dalton Trans., 2004, 2377-2385

Synthesis

Synthesis

M

M O

O

O

O

O

O

O

O

+ 2 LCO2H

L = M = Mo, W

Mo

Mo O

O

O

O

O

O

O

O

Mo

Mo O

O

O

O

O

O

O

O

W

W O

O

O

O

O

O

O

O

W

W O

O

O

O

O

O

O

O

Characterized by 1H NMR, MALDI-TOF

W

W O

O

O

O

O

O

O

O

W

W O

O

O

O

O

O

O

O

3 4

Mo

Mo O

O

O

O

O

O

O

O

Mo

Mo O

O

O

O

O

O

O

O

1 2

Absorption, - - - Excitation, Emission (r.t.), …. Emission (77K)

J. Am. Chem. Soc. 2005, 127, 17343-17352

4b

Observed short lived visible emission originating from 1MLCT (Mo2 )1 (O2C-aryl *)

Stokes shift larger than 1* M2 complexes (2000-3000 cm-1) smaller than previously reported for 3* Re2 (13 000 cm-1)

Vibronic progressions at 77K consistent with vibrations of aromatic carboxylic acid ligands

Solvent dependence ( 1200 cm-1 from THF to

DMSO)

Background: Part I

abs 1 abs 2

THF 440 nm 520 nm

CH2Cl2 420 nm 507 nm

MeCN 427 nm 504 nm

1

2

abs 3 abs 4

THF 610 nm 760 nm

CH2Cl2 576 nm 690 nm

MeCN 596 nm 732 nm (2:1 MeCN/THF mix)

3

4

Sonogashira Coupling

em (W2TiPB4): 815 nm

W2TiPB4

Dihedral angles between carboxylates and C6 plane:

29o and 67o

TRIR Time-resolved infrared (TRIR) spectroscopy

pump pulse: UV region (Nd:YAG laser) probe beam: infrared region.

Operates down to the picosecond time regime surpasses transient absorption and emission spectroscopy by providing structural information on

the excited-state.

Questions

EDIT Re Quad Bond, and look at orbital looks like delta star? Why do Mo 3MMCT lifetimes differ?

Have not mapped trends Why introducing thiophene to series? Why are ligand abs bound to W show less vibrations?

Perhaps because tungsten is coupling more – therefore less pure “ligand” transition

W interaction with ligands – orbital? Energetics of tungsten closer to ligand orbital energy – therefore

more overlap Explanation for lower energy W ex states having shorter lifetimes?

Since it’s a forbidden process (Triplet to ground state) – tungsten with greater spin orbit coupling makes it more allowable and therefore faster?

Have we done emission decay of singlet emission to match with fs-TA?

In yagna IC papers just say decays in less than 10 ns

Mo2 Triplet trends

Mo2(TiPB)4 = 43 ms Mo2(ThCO2)2 = 77 ms Mo2(ThCOS)2 = 50 ms Mo2(Th2CO2)2 = 83 ms Mo2(Th3CO2)2 = 72 ms Mo2(Tolyl2CO2)2 = 103 ms Mo2(AnthCO2)2 = 83 ms Mo2(BenzCN)2 = 93 ms Mo2(BenzNO2)2 = 79 ms Mo2(Benz2NO2)2 = 83 ms

Dimer-Dimers Mo2(TT) = 69 ms Mo2(DTT) = 60 ms Mo2(BT) = 72 ms