Electropolymerization of carbazole and 3,4 (etyhlenedioksithiophene) comonomer on carbon fiber microelectrode

Polikarbozol(PCz) ve poli(3,4 etilen dioksitiyofen)(PEDOT) ikisi de oldukça kararlı polimerlerdir. Fakat Poly(EthylCz) (PECz)’ün iletkenliği PEDOT’a oranla oldukça düşüktür. Polikarbazol ve PEDOT alternatif kopolimerleri sentezlendiğinde PCz’ün iletkenliğinin artırılması, her iki polimerin arasındaki etkileşimden dolayı homopolimerlerden daha üstün özellikleri olan bir kopolimer elde edilmesi amaçlanmıştır. Uç grubu Ecz olan Ecz-BEDOT-Ecz komonomeride sentezlenmiştir. Böylelikle BEDOT komonomeri yapısına Ecz’ü de katılarak komonomerin konjugasyon boyutu uzamıştır. Ecz-BEDOT-Ecz karbon fiber üzerinde polimerleşirken Platin üzerinde tıpkı Ecz homopolimerine benzer şekilde polimerleşmemiş sadece oligomer oluşumu UV spektroskopisinde gözlenmiştir. EBEE’nin karbon fiber üzerine kaplanması 1.3V uygulayarak 100mV/s tarama hızında döngülü voltamogram ile gerçekleştirilmiştir. Bu sonuç kullanılan elektrot tipinin polimeri-zasyon mekanizmasını etkilediğini kanıtlamaktadır. Kaplanan PEBEE’nin elektron transferine ait olan birinci redoks prosesi 0.88V’da, ikinci redoks prosesi ise 1.22V’dadır. Bu ikinci pikin çok daha yüksek olması orada hem komonomerin hemde kopolimerin bu potansiyelde oksitlenebilmesidir. Komonomerdeki ECz uç grubu; kopolimerin fiziksel özelliklerini iyileştirmeye büyük katkısı olmuştur. Elde edilen kopolimerin redoks davranışı Ecz’ün homopolimerine benzer özellik taşımaktadır. PEBEE’nin oksidasyon potansiyeli 0.4V’dur. Dolayısıyla PECz’dan daha küçüktür. Bu veriye dayanarak konjugasyon uzunluğunun arttığını ve elde edilen alternatif kopolimerin iletkenliğinin PECz’den yüksek olduğu sonucunu çıkarabiliriz. PBEDOT’ın oksidasyon potansiyeli düşük olduğundan oda koşullarında saklanamamaktadır. Alternatif kopolimer eldesiyle PBEDOT’ın kararlılığını arttırdığı görülmüştür. PEBEE’ yi homojen olarak karbon fiber üzerine kaplamak için pek çok koşul denenmiş, fakat en homojen kaplamanın  düşük polimerizasyon hızında (20mV/s) ve 50 döngü saysında elde edilebilmiştir. Anahtar Kelimeler: Cz, EDOT, elektropolimerizasyon, iletken polimer, karbon fiber.PEDOT, was initially developed to give a soluble conducting polymer that lacked the presence of undesired a-b, and b-b,couplings within the polymer backbone. Prepared using standard oxidative chemical or electrochemical polymerization methods, PEDOT was initially found to be an insoluble polymer,   yet exhibited some very interesting properties. In addition  to a very high conductivity,, PEDOT was found to be almost transparent in thin, oxidized films and showed a very high stability in the oxidized state. Polycarbazole, among conducting polymers, is attributed with good electroactivity, and useful thermal, electrical andphotophysical properties. However, p®p electron system along its backbone imparts rigidity to the polymer and, therefore, makes it infusible and poorly processable. Due to this reason, it was not initially employed as widely in devices as other conducting polymers. Recent advances in synthesis methods have, however, revived interest in polycarbazole . Investigations related to chemical modification or co-polymerization of carbazole with other monomers have led to the use of polycarbazole and its derivatives as redox catalysts, photoactive devices, sensors, electrochromic display, electroluminescent devices and biosensors . A new co-monomer EBEE has been firstly synthesized, characterized and electropolymerized on CFME and Pt. Side group of monomer play an important role on the physical properties of resulting copolymer and it resembles the behavior of homopolymer of monomer at the end of co-monomer,namely ethylcarbazole. Environmental stability of PBEDOT was increased by incorporation of ECz monomer into structure. For ECz ending monomers CFME seems better substrate than Pt to obtain an electroactive polymer film. EBEE comonomer synthesized first time and electropolymerized on Pt and CFME. ECz was also electropolymerized on CFME in order to compare with Poly(EBEE) and to gain further information. Cyclic voltammogram of electrogrowth  of Poly(EBEE) obtained on CFME ,exhibits two oxidative processes at 0.88V and 1.22 V. Appearance of green color on the electrode surface, higher value of current intensities inaccordance with Pt electrode and increase in the current density with increasing scan number suggests a polymer film on CFME. Although current intensities increase as the scan number increases, deposition process or insoluble film formation could not be detected in any experiments and the color of solution converted to blue when Pt electrode was used as a working electrode. Ex-situ UV of solution was taken during electropolymerization, the results indicated that when it is increased time exposed to potential amount of oligomer increased.This might be due to so-called oligomer approach that accepted recently. In this approach it is suggested that after the formation of a dimer a sequence of subsequent dimerization step leads to the formation of soluble oligomers. All this reaction probably occurs in solution without or only small precipitation on electrode. In our case after dimerization and/or tetramer formation further coupling reaction become very slow due to decrease in the rate constant. Formation of only soluble oligomers was also supported by solution color which turns from light yellow to green as reaction proceeds. In the light of all these results it can be concluded that  solubility of oxidized product of ECz-BEDOT-ECz  on Pt electrode might be due to either characteristic behavior of ECz  or stop of polymerization and/or became very slow at oligomerization level as suggested by oligomer approach. ECz-BEDOT-ECz polymerization mechanism depends on the switching potentials and chemical reaction became important at higher switching potential. The scan rate used have an effect on the homogenity of the resultant film. In literature, it is known that ECz is not electropolymerized in except acidic conditions; however, we observed that ECz can be electropolymerized on CFME under mentioned experimental conditions. CV of PECz coated CFME electrodes in monomer free electrolyte shows two step oxidation at 0.93V and 1.23 V which has promising properties and need to  further investigation. Comparison of results with previous study reveal the fact  that chemical make up play an important role on the properties of resulting polymers. The polymer obtained at 100mV/s and different cycle numbers polymer coating was heteregenous. Regular polymer growth is observed only 20mV/s scan rate with 50cycle. A globular structure resulting from a three dimensional nucleation growth mechanism as observed only in that case. The SEM structure of PEBEE shows small clusters of globules.The morphology of polymers obtained with 100mV/s scan rate were quite different from that of obtained with 20mV/s. Keywords: Cz, EDOT, electropolymerization, carbon fiber microelectrode