**1. Introduction**

118 Electropolymerization

Zhang, L.; Jiang, X.; Niu, L & Dong, S., (2006). Syntheses of fully sulfonated polyaniline and

*Bioelectronics*, Vol. 21, No. 7, pp. 1107-1115, ISSN 0956-5663

its application to the direct electrochemistry of cytochrome C, *Biosensors &* 

Electronically conducting polymers are a very popular research field among the chemists due to their use in a wide variety of marketable applications such as electrochromic devices [Mortimer et al., 2006; Sahin et al., 2005], polymer light-emitting diodes (LEDs) [Kraft et al., 1998], artificial muscles [Cortes & Moreno, 2003], gas sensors [Nicolas-Debarnot & Poncin-Epaillard, 2003], bio sensors [Geetha et al., 2006; Malinauskas et al., 2004] and corrosion protection of metals [Hosseini et al., 2007, 2008; Oco´n et al., 2005]. The preparation, characterization and application of electrochemically active, electronically conjugated polymeric systems are in the foreground of research activities in electrochemistry [Heinze et al., 2010]. Among the conducting polymers, polypyrrole has attracted a lot more interests [Jang & Oh, 2004; Zhang et al., 2006; Chang et al., 2009]. This polymer is easy to synthesize both chemically and electrochemically, exhibiting good electrical conductivity and relatively good stability under ambient conditions, but lacking good electroactivity and redoxability.

In order to improve the electroactivity and redoxability of the electro-synthesized polypyrrole, another molecule containing conjugated system can be used during the electropolymerization of pyrrole. 2,5-di-(2-thienyl)-pyrrole (SNS) is one of the molecules containing conjugated system and have been studied by various electrochemical methods such as cyclic voltammetry, chronopotentiometry, and chronoamperometry under different conditions (changing the electrolyte, electrode, electrochemical potential range and etc) [Otero et al., 1998; Brillas et al., 2000; McLeod et al., 1986].

Entezami et al. have studied the electropolymerization of pyrrole and *N*-methyl pyrrole in the presence of 1-(2-pyrrolyl)-2(2-thienyl) ethylene (PTE) and 2-(2-thienyl) pyrrole (TP) by cyclic voltammetry in different conditions [Kiani et al., 2001]. Recently, we have studied the electropolymerization of thiophene and 3-Methyl thiophene in the presence of small amount

Electrosynthesis and Characterization

**3. Results and discussion** 

a quasi-reversible behaviour.

scan rate 50 mV/s vs. Ag/AgCl

various scan rates was shown in figure 4.

**3.1 Electrochemical synthesize of polymers** 

of Polypyrrole in the Presence of 2,5-di-(2-thienyl)-Pyrrole (SNS) 121

components of the EIS in the complex plane were analyzed using the Zview(II) software to estimate the parameters of the equivalent electrical circuit. A computer-controlled

The electropolymerization of pyrrole was performed by cyclic voltammetry in the potential range of -100 to 900 *mV* through 15 scans. As shown in figure 1, at the first scan, there is an anodic peak at ca. 800 *mV*. By continuing electropolymerization through second scan, another anodic peak was observed at 550 *mV* indicating formation of polypyrrole. After the formation of black colored polymer film on the GC electrode surface, the electrode was taken out from electrochemical cell and was washed with acetonitrile. For the resulted polymer, the cyclic voltammograms at various scan rates were shown in figure 2 indicating

Fig. 1. Cyclic voltammograms of 7.4×10-3 M pyrrole in 0.1 M LiClO4 /CH3CN electrolyte at

The cyclic voltammetry investigations of SNS were carried out in the potential range of -400 to 1500 *mV* (Fig. 3). At the first scan two anodic peaks at ca. 570 and 1300 *mV* were observed resulting from the oxidation of SNS. In the backward scan from 1500 to -400 *mV*, there is one peak indicating a quasi-reversible reaction. At the second scan, a new anodic peak current was observed indicating formation of the electroactive poly(SNS) with an ionic structure. As shown in figure 3, after 7 scans, the second anodic peak at 1300 mV was eliminated. The cyclic voltammogram of poly(SNS) in the potential ranges between -400 to 1000 *mV* at

potentiostate (PARSTATE 2263 EG&G) was used for EIS measurements.

of 1-(2-pyrrolyl)-2-(2-thienyl) ethylene (PTE). It was found that the conductivity, electroactivity and redoxability of polythiophene and poly(3-methyl thiophene) are improved in the presence of PTE [Kiani et al., 2008a, 2008b].

In this work, the effects of conjugated molecule (SNS) on the electropolymerization and electrochemical behaviour of pyrrole was investigated. Firstly, the electropolymerization of pyrrole and SNS were carried out separately by CV method. Secondly, the electropolymerization of pyrrole in the presence of small amount of SNS was carried out and then the influence of SNS on the electropolymerization and electrochemical behaviour of pyrrole was investigated. In addition, the effect of SNS addition on the electron transfer reaction of ferro/ferricyanide redox system on the polypyrrole film was studied and finally the conductivity of poly(Py-SNS) was determined by electrochemical impedance spectroscopy (EIS) method.
