Electrochromic properties of a fast switching, dual colour polythiophene bearing non-planar dithiinoquinoxaline units

The synthesis and electropolymerisation of a new terthiophene, 1,3-di-2-thienylthieno[3′,4′:5,6][1,4]dithiino[2,3-b]quinoxaline, is reported. The compound bears a quinoxaline unit fused to the central thiophene ring via a 1,4-dithiin ring; the latter unit ensures a non-planar structure for the molecule. The corresponding polymer, prepared electrochemically, has been characterized by cyclic voltammetry and UV-vis-NIR spectroelectrochemistry. The material is oxidised within the conjugated chain, but the reduction processes are complex and arise from both the polythiophene and the independent quinoxaline units. The polymer has two distinct colour states—orange in the neutral form and green–blue in the oxidised state. Electrochromic studies on poly(1,3-di-2-thienylthieno[3′,4′:5,6][1,4]dithiino[2,3-b]quinoxaline) reveal fast switching speeds that are superior to those of poly(3,4-ethylenedioxythiophene) (PEDOT) and a colouration efficiency of 381 cm2 C−1 at 650 nm