Electrochimica Acta 46 (2001) 1207 – 1214 Spectroelectrochemical studies of the C 14 -alkyl derivative of poly(3,4-ethylenedioxythiophene) (PEDT) S. Garreau a , G. Louarn a, *, G. Froyer a , M. Lapkowski b,c , O. Chauvet a a Institut des Mate ´riaux Jean Rouxel, B.P. 32229, 44322 Nantes cedex 3, France b CEA Grenoble, DRFMC/SI3M/LPMS, 17 rue des Martyrs, 38054 Grenoble cedex 09, France c Department of Chemistry, Silesian Uniersity of Technology, 44100 Gliwice, Poland Received 25 August 2000 Abstract Spectroelectrochemical properties and electrical resistivity of an alkyl derivative of the poly(3,4-ethylenedioxythio- phene), PEDT-C 14 were investigated. The oxidative doping process of this polymer was studied by means of cyclic voltammetry, UV-vis-NIR optical absorption, Raman scattering and Electron Paramagnetic Resonance (EPR). The in situ conductivity on a Pt microelectrode was also monitored. Optical spectroscopies permit to follow the evolution of the different species that are present. Combination of these different techniques leads to the characterisation of the charged species that are induced by doping, and a mechanism of the modification of the electronic structure of PEDT-C l4 is proposed. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Poly(3,4-ethylenedioxythiophene) and derivatives; Raman scattering; In situ conductivity; EPR; In situ electrochemical spectroscopies www.elsevier.nl/locate/electacta 1. Introduction Polythiophene and derivatives have generated a large amount of research works for the last ten years [1]. But their main drawback was the instability of the conduc- tive form. The poly(3,4-ethylenedioxythiophene) shows a remarkable stability as compared to other members of the polythiophene family [2–4]. However it is still insoluble and its applications are thus limited to that of commercial dispersion in aqueous poly(styrenesulfonic acid) [5 – 7]. To overcome this problem, substitution with a long flexible alkyl chain would lead to soluble polymers as already reported in the polythiophene se- ries [8–10]. So, the insolubility of PEDT can be easily removed by substitution of an hydrogen atom in the oxyethylene ring by a long alkyl group. Soluble alkyl-substituted poly(ethylenedioxythiophene)s first synthesised by Ku- mar and Reynolds [11] are soluble in common organic solvents. They also retain their electroactivity after many redox cycles and can be made conductive via oxidative doping in solution. The aim of this paper is to report on PEDT substi- tuted with a long C 14 alkyl chain obtained by elec- trosynthesis. While previous papers focused on the electrochromic properties of this new polymer [12 – 14], here we deal with phenomena occurring during its doping process. We present detailed electrical resistivity, UV-vis and Raman spectroelectrochemical studies of PEDT-C 14 . Indeed, Raman spectroscopy has proven to be an ex- tremely useful probe for studying doping phenomena in conjugated polymers [15,16]. Although Raman spectra are complicated by resonance effects in nearly all conju- gated polymer systems, the use of different excitation * Corresponding author. E-mail address: guy.louarn@cnrs-imn.fr (G. Louarn). 0013-4686/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII:S0013-4686(00)00693-9