Benzothiadiazole, hexylthiophen and alkoxy benzene based solution processable copolymer: Effect of the electron withdrawing substituents (fluorine atoms) on electrochemical, optical and electrochromic properties.

4,7-Bis(4-hexyl-5-(trimethylstannane) -2-thienyl) −2,1,3-benzothiadiazole (HTBT) coupled with 2,5-bis (decyloxy)-1,4-dibromobenzene to afford the donor-π-bridge-donor-acceptor conjugated poly (4,7-bis (4-hexyl-2-thienyl) −2,1,3-benzothiadiazole-co-p-didecyloxybenzene) (PTBTB). Further, copolymerization of fluorine-functionalized HTBT moiety with alkoxyl benzene π-bridge using Stille crossing-coupling reaction yield PTBTB-F. The optical, electrochemical, fluorescent, spectroelectrochemical and electrochromic switching properties of two polymers with different acceptors are studied in detail. Both polymers exhibit excellent solubility in conventional organic solvents, high thermal stability and favorable fluorescence properties. The combination of a strong electron withdrawing pendant group (fluorine atoms) with benzothiadiazole (BT) backbone significantly influences the electrochemical redox, optical and electrochromic behaviors of conducting polymers. The introduction of fluorine atoms to BT lead to a higher oxidation onset potential, but an improved electrochemical n-doping process. The optical band gaps (E g ) of PTBTB and PTBTB-F films are calculated to be 2.02 eV and 1.91 eV, respectively. PTBTB and PTBTB-F films exhibited obvious and reversible color switching between their neutral and oxidized states with high optical contrasts as well as favorable response times, making the polymers unique candidates for flexible organic electrochromic device applications. [ABSTRACT FROM AUTHOR]