Linear and cross-linked mixed conducting polycarbazoles for electrochromic devices

Abstract

ABSTRACTA 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.