Effect of Conjugated Core Building Block Dibenzo[a,c]phenazine Unit on pi-Conjugated Electrochromic Polymers: Red-Shifted Absorption

A comparative investigation was undertaken for the electrosynthesis and electrochemical properties of three different electroactive polymers having a conjugated core building block, dibenzo[a,c]phenazine. A series of monomers has been synthesized as regards to thiophene based units; thiophene, 3-hexyl thiophene, and 3,4-ethylenedioxythiophene. The effects of different donor substituents on the polymers' electrochemical properties were examined by cyclic voltammetry. Introducing highly electron-donating (ethylene dioxy) group to the monomer enables solubility while also lowering the oxidation potential. The planarity of the monomer unit enhances pi-stacking and consequently lowering the E-g from 2.4 eV (PHTP) to 1.7 (PTBP). Cyclic voltammetry and spectroelectrochemical measurements revealed that 2,7-bis(4-hexylthiophen-2-ybdibenzo[a,c]phenazine (HTP) and 2,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-ybdibenzo[a,c]phenazine (TBP) possessed electrochromic behavior. The colorimetry analysis revealed that while PTBP have a color change from red to blue, PHTP has yellow color at neutral state and blue color at oxidized state. Hence the presence of the phenazine derivative as the acceptor unit causes a red shift in the polymers' absorption to have a blue color. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1714-1720, 2010