Molecular architecture: Another plausible pathway toward a low band gap polymer

A donor–acceptor–donor π-conjugated monomer (10,13-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)dibenzo[a,c]phenazine (PHED)) composed of bi-EDOT and dibenzo[a,c]phenazine repeat units was synthesized to examine the role of acceptor structure on the electronic and optoelectronic properties of the polymer. The spectroelectrochemical analysis showed that the introduction of electron-accepting unit results in a shift in the onset of the π–π* transition towards longer wavelengths. The optical band gap (Eg) for PPHED was found to be 1.10 eV and λmax was 790 nm. Switching ability of PPHED was evaluated by kinetic studies via measuring the percent transmittance as 80% at 1600 nm. The high optical contrast within the NIR region makes this material a good candidate for NIR device applications. Dual-type complementary colored electrochromic devices (ECD) using PPHED/PEDOT in sandwich configuration were constructed. Spectroelectrochemistry, switching ability and open circuit memory of the ECDs were investigated.