Linear and cross-linked mixed conducting polycarbazoles for electrochromic devices
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Linear and cross-linked mixed conducting polycarbazoles for electrochromic devices François Tran-Vana, Cédric Vancaeyzeelea, Thierry Henria, Juozas V. Grazuleviciusb, Claude Chevrota* a Laboratoire sur les Polymères et les Matériaux Electroactifs,(EA 2528), Université de Cergy-Pontoise, 5 mail Gay Lussac, 95013 Cergy Pontoise. FRANCE b Department of Organic Technology, Kaunas University of Technology, Radvilenu Plentas 19, LT 3028, Kaunas, LITHUANIA ABSTRACT A carbazole N-substituted by an oxyethylene group was polymerized using oxidative electro-polymerization. Due to the hydrophilic properties of the oligooxyethylene substituent, this monomer can be electropolymerized in aqueous solution. An acidic medium is particularly appropriate in order to decrease the oxidation potential of the monomer and to obtain films mainly composed of oligomers as revealed by SEC analysis. More particularly interesting is the stability of such material during polarization. In acidic medium 1.25 mol.L-1 HClO4, 95% of the charge density was maintained after polarization for 7000 cycles which shows the good electrochemical stability of this material compared to other polycarbazoles. Moreover, films are electroactive in aqueous electrolytes and would be well-compatible with polyethylene-oxide solid electrolytes. In order to increase the mechanical properties of the film, we have also electropolymerized an oligomer with pendant carbazole groups obtained by acid catalyzed cationic ring opening polymerization of [N(2,3-epoxypropyl)carbazole] which leads to a new dicarbazyl cross-linked polymer with cations solvating oxyethylene segments. Due to their tridimensional structure, the mechanical strength of these films is superior to that of a linear polycarbazole film. However, their electroactivity in aqueous electrolyte is poor. So, the electropolymerization of a mixture of both monomers ensures good mechanical properties and compatibility with hydrophilic electrolyte in view to prepare an electrochromic device.
INTRODUCTION Although less studied than other families of conducting polymers such as polyaniline, polypyrrole, polythiophene or polyparaphenylene, polycarbazoles are of particular interest with regards to their photoconductivity [1], electrochromic properties [2,3], use in electroluminescent devices [4], as biosensors [5] and other application [6]. Polycarbazole derivatives can be classified into two categories : π-conjugated linear carbazoles and non conjugated polymers containing pendant carbazoles. π-conjugated carbazoles are commonly obtained by electrochemical [7] or chemical [8] oxidation of carbazole derivatives in solution or from carbazole films deposited by evaporation under vacuum [9]. Moreover, some authors worked on non conjugated polymers with pendant carbazoles [1,10-12]. Polyvinylcarbazole (PVK) was the first of them [10]. Films of PVK can be obtained through electropolymerization of vinylcarbazole and lead to polymerization of the vinyl function [10-12]. In this field, electrochromic properties have been studied on po
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