RAPID COMMUNICATIONS

Synthesis and Electrochemical Properties of Poly ( 1,6-heptadiyne) Derivatives Containing a Carbazole Moiety

Keywords: conjugated polymer carbazole electrochemical electrochromic

INTRODUCTION

Electrically conducting polymers which can be processed into certain useful forms are of interest for their possible application to electronic and optical devices.'-3 In partic- ular, electrochemical and electrochromic properties of these conducting polymers are to be investigated in detail to find the specific applications such as optical storage, optical shutters, and display There are, however, only few reported polymer systems which possess the proper combined chemical and electrical properties.

We have recently reported the results of the work on synthesis and photoconductive properties of poly- [ bis (N-carbazolyl) -n -hexyl dipropargyl malonate] , [ poly- (BCHDPM) ] , which was a good example of homopolymer system with an intramolecular charge transfer complex?

In this study, we describe the results on the electro- chemical and electrochromic properties of poly ( BCHDPM) and poly ( BCHDPM-co-diethyl dipropargyl malonate) , poly ( BCHDPM-co-DEDPM) , by using cyclic voltam- metry and in-situ UV/Vis spectroscopy.

Measurement of Electrochemical Properties

To examine the electrochemical properties, the poly (BCHDPM ) films were formed by solution-coating method onto platinum foil as a working electrode with the area of 1 cm'. The films formed on the electrode were fully dried in a vacuum oven at room temperature. The thick- ness of the polymer film was approximately 0.5 pm. The electrochemical measurements were performed in 0.1M tetrabutyl ammonium perchlorate ( TBACIOl) /acetoni- trile solution. Silver wire and platinum foil were used as a reference and a counter electrode, respectively. Cyclic voltammetric waves were produced by using a Hokuto Denko HA-301 potentiostat/galvanostat equipped with a HA-301 functional generator and an X-Y recorder. In- situ UV-Vis absorption spectra of the polymer were ob- tained in a three-compartment electrochemical cell. Light from the source to the detector were delivered by two op- tical fibers which were connected to the Guided Wave Model 260 spectrophotometer. Distance between the probe and the working electrode was 1 cm. Circular platinum plate (diameter of 0.5 cm) , gold wire, and Ag/AgCl were used as working, counter, and the reference electrode, re- spectively.

EXPERIMENTAL

RESULTS AND DISCUSSION Polymer Samples

Polymer Poly (BCHDPM ) was prepared by metathesis polymer- ization with various transition metal catalyst systems. The procedure of synthesis was described in our previous study.8 Scheme 1 outlines the copolymerization of BCHDPM and DEDPM (BCHDPM to DEDPM mole ratio = 1 : 1). The structure and properties of the polymers obtained were analyzed by NMR (Bruker AC-200 spec- trometer), FT-IR (Bomem Michelson MB-100 spectrom- eter), and UV-Vis spectroscopic techniques (Shimadzu UV-3100s). Molecular weights and polydispersities of polymers were determined by GPC analysis with polysty- rene standards calibration (Waters 410).

Journal Of Polymer Science: Part A Polymer Chemistry, Vol. 32.2789-2792 (1994) 0 1994 John Wiley & Sons, Inc. CCC 0887-624X/94/142789-04

Copolymerization of BCHDPM and DEDPM was carried out with MoCls for 24 h in chlorobenzene to give violet polymer (yield 95% ) ? The resulting copolymer, poly ( BCHDPM-co-DEDPM) , was purified by washing with methanol and acetonitrile and characterized by IR, GPC, and 'H NMR." The number-average molecular weight (M,,) values of poly (BCHDPM) and poly ( BCHDPM-co-DEDPM) samples obtained here were about 6.8 X lo4 and 6.0 X lo4, respectively. UV-Vis spec- trum showed two major absorption peaks at 350 and 550 nm. The former value is due to the carbazole group and the latter one to the conjugated polyene. The resulting polymers exhibited good solubility in common organic solvents such as chloroform, tetrahydrofuran (THF), di-

2789

2790 J. POLYM. SCI. PART A POLYM. CHEM.: VOL. 32 (1994)

lyl + .$r Metathesis ~

Catalysts

R1 R1 R2

Scheme 1. Synthesis of BCHDPM-DEDPM copolymer by metathesis polymerization

methylformamide (DMF), etc., and were easily cast on glass plates to give violet, shiny thin films.

Electrochemical and Electrochromic Properties

The cyclic voltammograms of poly( BCHDPM) with the consecutive scan are shown in Figure 1. As the cycling number increased at the potential range of -0.5-1.5 V, poly (BCHDPM) showed the well-defined redox process and the increase of the current density in cyclic voltam-

I

0.4

0.3

0.2 - N E

4. E

.y 0.1

-

- 0 5 0 0.5 1 1.5

V vs . Ag/Agt

Figure 1. Cyclic voltammograms of poly (BCHDPM) with consecutive scan at 30 mV/s (0.1M TBAClO,/ace- tonitrile).

mograms. On the other hand, the oxidation occurred only at 1.4 V in the first scan, where the pendant carbazole units were oxidized and coupled each other irreversibly to form the dicarbazyls. After the first scan, two oxidation peaks a t 0.98 and 1.32 V were observed, which might be

A

~ ~

Potential. V vs. a/&+ Figure 2. Cyclic voltammograms of poly (BCHDPM) with various scan rate. (0.1M TBAClOJacetonitrile): ( a ) 20 mV/s, ( b ) 30 mV/s, ( c ) 50 mV/s, ( d ) 70 mV/s, ( e ) 100 mV/s.

RAPID COMMUNICATIONS 2791

attributed to the dicarbazyls coupled. These electrochem- ical properties are similar to those of N-alkyl carbazole derivative^."-'^ Figure 2 shows the variation of the redox peak current density as the various scan rates to inves- tigate electrochemical kinetic behavior. The peak potential shifts are almost independent of scan rate. Also, the redox current value increased as the scan rate increased. This result suggests that electrochemical process is reproducible in the potential range of 0.0-1.5 V vs. Ag/Ag+. It has been reported that the relationship between redox peak current and the scan rate can be expressed as a power- law type equation [ see eq. ( 1 ) ] : l 4 3 l 5

ip,, = kv' (1)

where = oxidative peak current density, u = scan rate, k = proportional constant, and x = exponent of scan rate.

As shown in Figure 3, the oxidation current density according to the scan rate is approximately linear in the range of 20-100 mV/s. The exponent of scan rate, x value obtained from Figure 3, was found to be 0.6 indicating that the kinetics of the redox process is almost controlled by the diffusion pro~ess . '~ This means that insertionlde- sertion of C10; ions is responsible for the charge electro- neutrality during the redox process of poly (BCHDPM) . The cyclic voltammograms of poly (BCHDPM-co- DEDPM) with several scans are shown in Figure 4. Although the density of carbazole moiety was relatively small in the copolymer system as compared with poly-

0.6

0.4

0.2

0

B 0.0

i .r(

-0.2

-0.4

1.32\

1 . 1 . 1 . 1 . 1 . 1 .

1.2 1.4 1.6 1.8 2.0 2.2 2.4

Log u (mV/sec)

Figure 3. Plot of log ip,a vs. log u for poly (BCHDPM).

t

T Potential. V vs. Ag/Ag'

Figure 4. Cyclic voltammograms of poly (BCHDPM- DEDPM) with consecutive scan at 30 mV/s (0.1M TBAClO,/acetonitrile) .

(BCHDPM) , the characteristics of redox were shown to be similar. However, it was found that the redox peak current density of copolymer was larger than that of poly(BCHDPM) at similar conditions. It might be at- tributed to the easier diffusion of C10; species in the co- polymer. The in-situ optical absorption spectra of poly ( BCHDPM-co-DEDPM) at various potential (0-1.4 V) are shown in Figure 5. Poly(BCHDPM-co-DEDPM) shows the maximum absorption peak at around 350 nm

I

0 3hO 400 500 6bO 760 800 960 1000

Wavelength (nm)

Figure 5. co-DEDPM) at various potentials.

In-situ UV/Vis spectra of poly(BCHDPM-

2792 J. POLYM. SCI. PART A: POLYM. CHEM.: VOL. 32 (1994)

due to the carbazole groups and has a relatively larger absorption in oxidation state at above 500 nm wavelength than in reduction state. It was observed that the color of the poly (BCHDPM-co-DEDPM) changed from trans- parent light-yellow in reduction state to dark-green in ox- idation state, respectively.

The authors gratefully acknowledge the support of this work by the Korea Science and Engineering Foundation.

REFERENCES AND NOTES

1. A. 0. Patil, Y. Ikenoue, F. Wudl, and A. J. Heeger, J. Am. Chem. Soc., 109,1858 ( 1987).

2. S. H. Askari, S. D. Rughooputh, and F. Wudl, Synth. Met., 29, El29 (1989).

3. A. 0. Patil, A. J. Heeger, and F. Wudl, Chem. Rev., 88,183 ( 1988).

4. G. Gustafsson, Y. Cao, G. M. Treacy, and F. Klavetter, N. Colaneri, A. J. Heeger, Nature, 357, 477 ( 1992).

5. K. Faid, R. Cloutier, and M. Leclerc, Macromolecules, 26,2051 (1993).

6. Z. Yang, I. Sokolik, and F. E. Karasz, Macromolecules, 26,1188 ( 1993).

7. A. R. Hepburn, J. M. Marshall, and J. D. Maud, Synth. Met., 41-43, 2935 (1993).

8. J. W. Park, J. H. Lee, H. N. Cho, and S. K. Choi, Macromolecules, 26, 1191 (1993).

9. [ MIo, initial monomer concentration = 0.25, monomer to MoC16 molar ratio = 50, temperature = 60°C.

10. 'H-NMR (CDC13), G(ppm): 1.2-1.9 [ -(CH2),--], 2.8 (-CHzCE),4.0-4.2 (CO&HP--, -CHzN), 6.7 (conjugated polyene) , 7.0-8.0 (carbazole).

11. J. H. Lee, J. W. Park, J. M. KO, Y. H. Chang, and S.

12. J. F. Ambrose, L. L. Carpenter, and R. F. Nelson, J.

13. B. R. Hsieh, K. Abbey, and M. H. Litt, Mucromole-

14. A. J. Bard, and L. R. Faulker, Electrochemical Meth-

15. J. M. KO, H. W. Rhee, S. M. Park, and C. Y. Kim, J.

K. Choi, Polym. Bull., 31, 339 (1993).

Electrochem. Soc., 122,876 (1975).

cules, 19, 521 (1986).

ods, Wiley, New York, 1980, chapters 3, 6, and 10.

Electrochem. Soc., 137,905 (1990).

JONC-WOOK PARK' JI-HOON LEE'

HYUN-NAM C H O ~ SAM-KWON CHOI',*

JANC-MYOUN KO2

' Department of Chemistry *Department of Chemical Engineering Korea Advanced Institute of Science and Technology 373-1 Kusung-dong Yusung-Gu, Taejeon, Korea 3Polymer Material Laboratory Korea Institute of Science and Technology P.O. Box 131 Cheongyangri, Seoul, Korea

Received March 1, 1994 Accepted May 17, 1994

* To whom all correspondence should be addressed.