ELSEVIER Synthetic Metals 84 (1997) 215-216 ELECTROCHEMICAL SYNTHESIS AND SPECTROSCOPIC STUDY OF POLY(3,4-METHYLENEDIOXYTHIOPHENE) H. J. Ahonen*, J. Kankare, J. Lukkari and P. Pasanen Department of Chemistry, University of Turku, FIN-20014 TURKU, FINLAND Abstract Electropolymerization of a new thiophene derivative 3,4methylenedioxythiophene was studied on indium tin oxide electrodes and platinum in difJerent organic solvents (acetonitrile, propylene carbonate, and nitrobenzene). Electropolymerization potentiodynamically in anhydrous nitrobenzene resulted in best polymeric films, which were compact and tightly adhered to the substrate surface. The properties of thesefilms were compared to those pr~iouslypublishedforpoly(3,4-ethylenedioxythiophene). Keywords: Electrochemical polymerization, polythiophene and derivatives, in-situ electrochemical spectroscopy, UV-Vis-NlR absorption. 1. Introduction Poly(alkylenedioxythiophene)s have been reported to have some intriguing properties such as high electrochemical stability, high conductivity and transparency in their doped form [l-3]. These polymers consist of monomer units which have electron donating oxygen atoms stabilizing the monomer radical cation and thus lowering the band gap of the polymer. The size and planarity of oxygen ring, however, is supposed to have some effect on the polymer properties. 3,4- Methylenedioxythiophene (MDOT) molecule is more planar than its ethylene or trimethylene analogues so it should form more conjugated polymer. We have electrosynthesized PMDOT to compare its properties to those previously published for poly(3,4-ethylenedioxythiophene) (PEDOT). 2. Experimental 3,4-Methylenedioxythiophene was synthesized in our laboratory and the synthesis will be published separately [4]. Electropolymerizations were performed in anhydrous nitrobenzene (NB, Fluka), propylene carbonate (PC, Aldrich) and acetonitrile (AN, Lab-Scan). Solvents were stored over 4A molecular sieves under argon atmosphere and used as such. All the spectroelectrochemical experiments were performed in dry acetonitrile. Tetrabutylammonium hexafluorophosphate (TBAP, Aldrich) was dried at 110 ‘C over P205 in vacuum and the solution was stored over activated alumina under argon atmosphere. The spectroelectrochemical system and the electrochemical cell were similar to those described in previous studies [5]. The potential of the ferrocene/ferricenium couple was found to be + 630 mV as referred to the Ag pseudoreference electrode. Both platinum and IT0 electrodes were used as working electrodes. Their surface areas were * Corresponding author. 0379-6779/97/$17.00 0 1997 Elsevier Science Sk All rights reserved PIISO3794779(96)039104 0.28 cm*. A stainless steel plate was used as an auxiliary electrode. UVlVis-NlR spectra were recorded on a Varian Cary 5 Spectrophotometer. 3. Results and discussion 3.1 Electropolymerization of 3,4-methylenedioqthiophene The qualities of the materials obtained by electrochemical polymerization were drastically dependent on the polymerization conditions. No polymer formation was observed when PC was used as solvent. Only soluble oligomers were observed in the vicinity of working electrode during electropolymerization trials. Using AN as solvent, black powdew deposits form at the electrode surface when high anodic potentials are applied (2.5 V vs. Ag). Potential / V (vs. Ag) Fig. 1. Multisweep voltammogram of 0.1 M MDOT in 0.1 M TBAP/NB on a IT0 electrode. Scan rate 100 mV/s. 20 Cycle between 0.0 V and 1.6 V. Every other cycle is drawn.