Dibenzothiophene-thiophene hybrid electrochromic polymer: effect of media on electrosynthesis and optical properties

π-Conjugated monomer, namely 2,8-bis-(4-octoxythiophen-2-yl)-dibenzothiophene (DBT-3OctTh), containing dibenzothiophene moiety as the central unit and 3-octoxythiophene as the external unit have been synthesized via Stille coupling reaction. The monomer was obtained as white powder in a yield of 75 %. Its electropolymerization was comparatively investigated in different media (dichloromethane (DCM), propylene carbonate (PC), or boron trifluoride diethyl etherate (BFEE)), all using Bu4NPF6 as the electrolyte. In BFEE, DBT-3OctTh revealed the lowest onset oxidation potential (0.67 V vs. Ag/AgCl) than DCM (1.12 V) and PC (1.13 V), leading to a facile electrodeposition to prepare poly(2,8-bis-(4-octoxythiophen-2-yl)-dibenzothiophene) (PDBT-3OctTh) with less possibility occurring on the side reactions. Doping level was calculated to be 0.32 in DCM, 0.12 in BFEE, and 0.04 in PC, respectively. The structure and performances of as-prepared polymers were systematically studied by cyclic voltammetry and spectroelectrochemistry. Spectroelectrochemical analysis revealed that PDBT-3OctTh films prepared in these media all switched light grey in the neutral state whereas blue in the oxidized state. Further, the existence of polaron or/and bipolaron in the oxidation process demonstrated that PDBT-3OctTh was p-dopable.