Chemosynthesis, characterizations and electrochromic properties of a novel solution-processable donor-acceptor type copolymer

Chemical copolymerization of 4, 7-bis (4-hexyl-5-trimethylstannyl-2-thieny l) -2,1,3-benzothiadiazole and 2, 5-didecyloxy-1,4-dibromobenzene was carried out in refluxed toluene with bis (triphenylphosphine) palladium(II) chloride (Pd(PPh3)2Cl2) as catalyst to give donor-acceptor type poly (4, 7 -bis (4-hexyl-2-thienyl) -2,1,3-benzothiadiazole-co-p-didecyloxybenzene) (PTBTB) via Stille-coupling reaction. Spectroelectrochemical and electrochromic properties of the resulting copolymer were characterized by cyclic voltammetry (CV) and UV-Vis-NIR spectroscopy. Cyclic voltammetry showed a definite electrochemical redox behavior of PTBTB polymer during the p-doping progress and an explicit reduction peak at about -1.4 V at the n-doped state. And spectroelectrochemical studies demonstrated that the hybrid polymer film had distinct electrochromic properties with color changing from red in the reduced form (0 V) to light gray upon step-wise oxidation (1.03 V) and tile blue at the fully oxidized state (1.4 V). Further kinetic studies results indicated that the hybrid polymer had decent optical contrast ratios (34.3% for 517 nm and 65.2% for 1600 nm), favorable coloration efficiency (238 cm2/C) and fast response time (0.6 s). The material hold promise for electrochromic applications.