Synthesis of novel thermally stable electrochromic polynorbornenes containing symmetrical diarylamine and unsymmetrical triarylamine chromophores via ring-opening metathesis polymerisation

Abstract

A new electrochromic norbornene derivative (NB) containing symmetrical diphenylamine and unsymmetrical triphenylamine groups, was synthesised from norbornene amine and unsymmetrical triphenylamine-substituted bromide. NB was used to obtain unsaturated PNB via ring-opening metathesis polymerization using different Grubbs' catalysts, followed by hydrogen reduction to obtain saturated HPNB. PNB and HPNB were highly soluble in common organic solvents such as toluene, xylene, benzene, chlorobenzene, 1,2-dichlorobenzene, and tetrahydrofuran at room temperature. The glass transition temperatures (Tg) of PNB and hydrogenated HPNB were 162 °C and 117 °C, respectively. The 10% weight-loss temperatures of PNB and hydrogenated HPNB were 410 °C and 450 °C, respectively. Cyclic voltammogram of HPNB film cast onto an indium-tin oxide (ITO)-coated glass substrate exhibited three reversible oxidation redox couples at 0.52, 0.85 and 1.30 V versus Ag/Ag+ in acetonitrile solution. The electrochromic characteristics of HPNB showed excellent stability and reversibility, with multi-staged colour changes from light yellow to green, dark-blue and purple as the potential changed from 0 to 1.35 V. The colour switching time and the bleaching time of the HPNB were 8.7 s and 4.3 s, respectively, at 1084 nm and 7.9 s and 3.8 s at 879 nm.