Photoluminescence properties of various polythiophene derivates

ELSEVIER

Synthetic

Photoluminescence

Metals

69 (1995) 377-378

properties of various polythiophene

derivatives

Tai Jong Kang,a Jae Yong Kim,a Kyung Joon Kitr~,~ Changjin Leeb and Suh Bong Rheeb aDepartment bAdvanced

Abstract Electronic Fluorescence

absorption

and

measurements

of Chemistry,

Taegu University,

Kyoungsan

713-714 Korea

Polymer Division, Korea Research Institute of Chemical Technology, P.O.Box 107, Taejeon, 305-606 Korea

photoluminescence

indicate

that

higher than that of the alkyl containing

characteristics

fluorescence

derivatives.

quantum

of various

efficiency

polythiophene

of the ester

Among the ester group substituted

derivatives

containing

have

polythiophene

polythiophenes,

been

studied.

derivatives

the longer alkyl

are

side chain

gives higher quantum efficiency. The quantum yield of the polythiophene derivatives in solution is compared with the coumarin 500 laser dye. Electronic absorption and emission peak shift to the shorter wavelength are observed with increasing temperature.

1. INTRODUCTION An

alkyl

extensively

polythiophene

has

studied conducting

characteristics other

r been

polymers

such as good solubility,

interesting

optical

and

one

of

polythiophene

derivatives

conformational

change

easy processability

thermal

advantage

of studying

are

properties

generally

and the conjugation polythiophenes

most

because of its peculiar

purposes. l-3 The optical and thermal

application

the

and

for

many

properties

associated

to

of

R=

R

d I

+ra

PPET

-kSC&

PHET

R

n

PDET

-c-v%9

- P C%ciH-cn,

the

length. One of the

is that the properties

of

PMBET

C%

R=

R

POT-PPET (m:n=l:l)

-C-ctHs

this polymer can be easily modified by changing the substituent or the size of the alkyl side chain, which makes a systematic study possible. In this work, the optical spectroscopic prepared

alkyl ester polythiophenes

compared

properties

of newly

have been investigated

and

with widely studied alkyl thiophenes.

3. RESULTS AND DISCUSSION Fluorescence derivatives

2. EXPERIMENTAL

quantum

yield

has been measured

of

listed value is relative to coumarin

ester substituted

side chain polymers

are synthesized. are reported

polythiophene

Details

elsewhere.4

derivatives

given as follows.

polythiophenes

Electronic

and

their

absorption

with varying

on preparation The repeating abbreviated spectrum

alkyl

of these unit of the names

are

was measured

with Shimadzu 160A UV/Vis spectrophotometer. Fluorescence spectrum was recorded using a SPEX Fluoromax, and the fluorescence quantum yield of polythiophene derivatives in dichloromethane was measured and compared with coumarin 500 laser dye. The polymer the oxygen

quenching

these samples.

solutions

were not degassed

of the fluorescence

Temperature

is not important

of the sample is controlled

+ 0.5 “Cby Neslab RTE- 110 circulator

since in

within

unit.

0379-6779/95/$09.50 0 1995 Elsevier Science S.A. All rights reserved SSDI 0379-6779(94)02494-J

more

strongly

fluorescent

than

Among alkyl ester thiophenes, gives higher fluorescence already

been observed

polythiophene in Table 1. The

500 laser dye. It is observed

that alkyl ester polythiophenes(PPET, Alkyl

several

and compared

PMBET and PDET) are

alkyl

thiophenes

like

POT.

one with longer alkyl side chain

quantum

yield. Similar

in the electro-

effects

have

and photoluminescence

study of alkyl thiophene derivatives. 2a In a related study of thiophene oligomers,5 fluorescence intensity increases with increasing thiophene chain length. It is also observed that the fluorescence quantum yield of all the polythiophenes studied decreases with increasing temperature in the liquid state. This is because the motion of the alkyl side chain gets more flexible as temperature

goes up and more nonradiative

in the dissipation

of the electronic

energy.

paths are involved

378

T.J. Kang et al. / Synthetic

Table

1. Fluorescence

derivatives

measured

quantum

yield of various polythiophene

for dichloromethane

solution

Metals 69 (1995) 377-378

Table 2. Electronic polythiophene

absorption

derivatives

and emission

at room

maxima

of various

temperature.

(Emission

maxima are denoted by numbers in the parenthesis) polythiophenes

fluorescence

quantum

yield

0.24

film _____

toluene

CH7,ClP

443(575)

434(577)

387(607) _____

390(559) 412(561)

392(559) -----(561)

polythiophenes

(relative) POT

POT

PPET

0.42

PPET

PMBET PDET

0.52 0.50

PHET PDET

415

0.40

PMBET

415(602)

412(559) 412(561)

412(559)

POT-PPET

1.00

POT-PPET

456

428(573)

430(573)

Coumarin

500

observed wavelength

in the absorption spectra. The spectral shift to the blue temperature is related at elevated to a

conformational

transition

that is responsible In table 2,

from the planar to nonplanar

for shortening

of the conjugation

peak positions

of absorption

listed for several polythiophene Alkyl

ester

and

wavelength

that results

chain, length. 500

600

700

800

which

chain4

peak

absorption

spectra of PDET

the band gap energy with longer alkyl side

to an increased

toluene

thiophenes,

and

intermolecular

of the better

with longer alkyl

to note that the emission compared

maxima of the to the emission

maxima remain almost

data of electronic

dichloromethane

the

conjugation

with the observation

the same. From the spectroscopic for

the

shorter

of band gap energy.

for the alkyl ester polythiophenes

It is interesting

both

the

derivative

maxima in solution while the absorption

and POT films at different temperatures.

to

are

media.

series,

can be attributed

This is consistent

makes

shift

in the increase

film appear at the longer wavelength Figure 1. Electronic

in different

on polythiophenes emission

smaller for thiophene

crystallinity

(m-n)

the

structure

length.3

and emission

derivatives

the alkyl ester thiophene

becomes

wavelength

substitution

absorption Within

413(561)

solutions interactions

of

transition alkyl

ester

are regarded

as

being short range repulsive. ACKNOWLEDGMENT TJK

and

JYK

NONDIRECTED Foundation,

were

supported

RESEARCH

in

FUND,

part Korea

by

the

research

1993.

REFERENCES

600

500

400

wavelength

1. M. Sato, S. Tanaka and K. Kaeriyama, Chem. Commun., (1986) 873.

600

700

2. a) K. Yoshino,

(nm)

and Y. Ohmori, Figure 2. Fluorescence

emission spectra of toluene

Tashiro,

In Figures different

The

1 and 2, temperature emission

temperatures

wavelength

spectra

dependent of both

are well resolved

with increasing

temperature.

POT

spectral

shift

is

and PDET

at

and shift to the shorter Similar situation is

Synth.

Y. Minagawa,

M. Uchida, Met.,

55-57

M. Kobayashi,

Sot.,

K. Muro, T. Kawai (1993)

28. b) K.

S. Morita, T. Kawai

and K. Yoshino, Synth. Met., 55-57 (1993)321. 3. M. Leclerc, C. Roux and J.-Y. Bergeron, Synth. Met., 55-57

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shown.

S. Morita,

J. Chem.

(1993) 287. 4. C. Lee, K. J. Kim, and S. B. Rhee, in these proceedings. 5. H. Chosrovian, S. Rentsch, D. Grebner, D. U. Dahm, Birckner,

and H. Naarmamr, Synth. Met., 60 (1993) 23.

E.