Electrochimica Acta 53 (2008) 7054–7060 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta In situ FTIR spectroelectrochemistry of poly[2-(3-thienyl)ethyl acetate] and its hydrolyzed derivatives Andrea Kellenberger a,b , Evelin J ¨ ahne c , Hans-J ¨ urgen Adler c , Taruna Khandelwal c , Lothar Dunsch a,∗ a Leibniz-Institute of Solid State and Materials Research, Department of Electrochemistry and Conducting Polymers, Helmholtzstrasse 20, D-01069 Dresden, Germany b University “Politehnica” of Timisoara, Faculty of Industrial Chemistry and Environmental Engineering, Piata Victoriei 2, RO-300006 Timisoara, Romania c Technische Universit¨ at Dresden, Chair of Macromolecular Chemistry and Textile Chemistry, Mommsenstrasse 4, D-01069 Dresden, Germany article info Article history: Received 30 January 2008 Received in revised form 7 May 2008 Accepted 9 May 2008 Available online 18 May 2008 Keywords: In situ spectroelectrochemistry Vibrational spectroscopy Soluble conducting polymers Polythiophenes Doping abstract Poly[2-(3-thienyl)ethyl acetate] (PTEtAc) was chemically synthesized and transformed to partially hydrolyzed PTEtAc (PTEtAcOH) and poly[2-(3-thienyl)ethanol] (PTEtOH). The influence of the acetoxy and hydroxyl terminal functionalities in the side groups on the electrochemical properties of these polyalkylth- iophenes was studied by cyclic voltammetry and in situ FTIR spectroelectrochemistry. The cyclic voltammograms point to a chemically reversible behaviour of the p-doping process for PTEtAc and PTE- tAcOH, while for PTEtOH the redox activity of the polymer film is lost during consecutive potential scans. The attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was used to inves- tigate the p-doping of the three different type of thiophene polymer films. In situ FTIR spectra taken at different electrode potentials in a cyclovoltammetric scan display the doping induced changes of the polymer pattern. Important differences in the behaviour of the polymers were observed and interpreted in terms of different film structures. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction Conjugated polymers have found numerous applications in dif- ferent fields like rechargeable battery electrodes, electrochromic devices, chemical and optical sensors, light-emitting diodes, molec- ular based devices, field-effect transistors and supercapacitors [1,2]. One of the main challenges is the search for conducting polymers with improved solubility and processability but these properties should not affect their electrical properties, i.e. con- ductivity. For polymers like polythiophene one of the methods suggested for this purpose is the introduction of a substituent in the 3- and/or 4-position of the thiophene ring. High conductivities were obtained by this strategy for electrochemically synthesized poly(3-methylthiophene) and poly(3-ethylthiophene) [3]. How- ever, an appropriate solubility in common organic solvents has been achieved only with an alkyl side chain of more than four carbon atoms [4]. For practical purposes it is interesting to have polymeric materials available based on poly(3-alkylthiophenes) (P3AT) functionalized with different reactive groups. Thiophenes functionalized with -alkyl-phosphonic acid [5] and -alkyl- trichlorosilane groups [6] have been successfully prepared and ∗ Corresponding author. Tel.: +49 351 4659660. E-mail address: L.Dunsch@ifw-dresden.de (L. Dunsch). used in the formation of self-assembled monolayers with potential applications as protective coatings, sensors, electronic semiconduc- tors or adhesive systems. Poly(3-alkylthiophenes) functionalized with hydroxyl groups are valuable in immobilizing enzymes for sensor systems. However, thiophene monomers with reactive hydroxyl groups can only be polymerized after the protection of –OH group through etherification or esterification. After polymer formation, the protected –OH group can be recovered by ether or ester cleavage via acidic or basic hydrolysis. This approach lead to the electropolymerization of 3-(2-methoxyethyl)thiophene [7] but gave no result for the homopolymerization of various esters of 2-(3-thienyl)ethanol [8]. Recently, the electrochemical polymer- ization of 2-(3-thienyl)ethyl acetate has been reported at high monomer concentrations and relatively low electrode potentials [9]. One of the attractive properties of the ester-functionalized polyalkylthiophenes is their good solubility in common organic solvents resulting in the casting of homogeneous, free-standing films [10]. Despite of their interesting properties, their doping mechanism was rarely studied. To the best of our knowledge, there are only a few studies using the UV–vis spectroelectro- chemical characterization of ester-substituted polyalkylthiophenes [9]. Vibrational spectroscopy has proved to be a powerful technique for the study of conjugated polymers [11–14]. The infrared spec- tra of conjugated polymers in their conducting (doped) states are characterized by the appearance of very intense infrared active 0013-4686/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2008.05.025