Enhanced redox stability and optical contrast of electrochromic copolymers from selenophene and 3-methylthiophene

Abstract

A series of poly(selenophene-co-3-methylthiophene) films were synthesized by electrochemical copolymerization of selenophene and 3-methylthiophene under different feed ratios in tetrahydrofuran–boron trifluoride diethyl etherate (THF–BFEE) mixture. Structural interpretation, surface morphology, and electrochemical and electrochromic properties of the resultant copolymer films were determined and comparatively discussed. These copolymer films displayed reversible color changes from sandy-brown in the neutral state to deep blue and black in the oxidized state, clearly different from their parent homopolymers polyselenophene and poly(3-methylthiophene). The copolymers also showed more favorable electrochromic kinetic parameters in comparison with both of their homopolymers, including higher optical contrast, faster switching time, more efficient coloration efficiency, and better optical memory. Under the monomer feed ratio of selenophene/3-methylthiophene in 1:2, the copolymer film exhibited the highest optical contrast of 70% at 1080 nm. Furthermore, excellent redox stability was observed for all the copolymers after secondary electrochemistry doping by cyclic voltammetry in monomer-free BFEE.