Synthesis of electroactive benzimidazole derivatives and their electrochromic properties

Özelçağlayan, Ali Can
In order to study their electrochemical and optical properties, two donor-acceptordonor (D-A-D) type monomers; 4'-(tert-butyl)-4,7-bis(4-hexylthiophen-2- yl)spiro[benzo[d]imidazole-2,1'-cyclohexane] (BIHT) and 4'-(tert-butyl)-4,7-bis(2,3- dihydrothieno[3,4-b][1,4]dioxin-5-yl)spiro[benzo[d]imidazole-2,1'-cyclohexane] (BIED), were electrochemically polymerized. These properties were investigated by cyclic voltammetry and UV–Vis-NIR Spectroscopy techniques. Effects of different donor groups; 3-hexylthiophene and 3, 4-ethylenedioxythiophene (EDOT), on new benzimidazole group, 4'-(tert-butyl)spiro[benzo[d]imidazole-2,1'-cyclohexane], were investigated. These pendant groups cause slight differences in optical band gaps, which are 1.19 eV for PBIHT, 1.15eV for PBIED. PBIHT and PBIED have both nand p- doping. Both of them have broad absorption in the visible region. In NIR region, both polymers revealed 46 % transmittance with high switching times. PBIED and PBIHT showed multichromic properties. PBIED is green at neutral state. For the most oxidized and reduced states, it is blue and red, respectively. PBIHT is blue at neutral state, transmissive-gray in oxidized state and transmissive greenishgray in reduced state.