Low band gap polymers synthesized by electrochemical polymerization for electrochromic devices

Two novel monomers, 10,13-bis(4-octyl-2-thienyl)-dibenzo[a,c]phenazine (OTBP) and 10,13-bis(4-octyl-2-thienyl)-dipyrido[3,2-a:2′,3′-c]phenazine (OTPP), were synthesized. Electrochemical polymerization of OTPP and OTBP were carried out in acetonitrile/dichloromethane (ACN/DCM) solvent mixture containing tetra-n-butylammoniumhexafluorophosphate (TBAPF6), and electrochromic properties of POTPP and POTBP are described. Furthermore, the effects of structural difference on electronic properties of electron acceptor units, electrochemical and electrochromic properties of two resulting polymers were examined. The results showed that the OTBP was polymerized at lower potential than OTPP, and this is because OTPP contains two more N atoms in electron acceptor unit and its electron withdrawing ability is stronger than that of OTBP. The UV-Vis-NIR spectra analysis revealed that the POTPP film has three absorption bands centered at 570 nm, 925 nm and 1581 nm, and the POTBP film has two absorptions at 566 nm and 1009 nm, respectively. The electrochromic properties indicated that the two polymer films exhibits reasonable optical contrasts and response time with low band gaps, defined as the onset of the absorption band at 570 nm for POTPP and the absorption band at 566 nm for POTBP, as 1.74 eV for POTPP and as 1.69 eV for POTBP.