Optical and electrochemical properties of soluble N-hexylcarbazole-co-3,4-ethylenedioxythiophene copolymers

We synthesised soluble N-hexylcarbazoie-co-3,4-ethylenedioxythiophene (HCz-co-EDOT) copolymers from mixtures in various ratio of the two corresponding dihalogenated monomers. From EDOT-HCz starting molar ratio: 0.25, 1,4, we obtained random copolymers named, respectively, C1, C2 and C3 and we compared their properties to the two homopolymers synthesised in the same way. The Infra red studies clearly indicated, as expected, that an increase in the amount of ethylenedioxythiophene in the feed composition leads to an increase of the proportion of the corresponding comonomer in the final materials. Elemental analysis point out that the reactivity of dibrominated EDOT seems slightly lower than that of dibrominated HCz. Thin films of copolymer have been prepared and their electrochemical response have been investigated. Absorption and luminescence of these materials have been also studied in CHCl3. Copolymers mainly composed of one monomer (C1 and C3) behaves like the corresponding homopolymers. On an other hand, copolymer (C2) obtained from an equimolar amount of each monomer in the feed composition clearly exhibits distinct signals in optical spectra and in electrochemical behaviour, probably due to the presence of each monomer unit short segments. So, the use of C2 has been explored for possible application in light emitting devices indicating that the p-doping of the material would be facilitated leading to an improved hole injecting when compared to carbazoles homopolymer. It could be particularly interesting as a hole transporting layer in multilayer organic light emitting devices. (C) 2001 Elsevier Science B.V. All rights reserved.