Synthesis of two novel acenaphthyl-quinoxaline based low-band gap polymers and its electrochromic properties

Abstract

Two novel π-conjugated monomers, 8,11-bis(4-octyl-2-thienyl)-acenaphthyl-[1,2-b] quinoxaline (OTAQ) and 8,12-bis(4-octyl-2-thienyl)-acenaphthyl-[1,2,5]thiadiazolo[3,4,i]quinoxaline (OTATQ), were synthesized. These polymers contains on type electron donating unit 3-octylthiophene and two type of electron withdrawing unit that acenaphthyl-quinoxaline in OTAQ and acenaphthyl-thiadiazolo-quinoxaline in OTATQ, respectively. Electrochemical polymerization of the monomers were carried out in acetonitrile/dichloromethane soluvent mixture containing tetra-n-butylammonium hexafluorophosphate and electrochromic properties of polymers are described in this paper. Furthermore, the effects of structural difference on electrochemical redox behavior and spectroelectrochemical properties of the two resulting polymers were examined. The results showed that an anodic wave at +0.56 V vs Ag wire pseudo-reference electrode corresponding to the monomer OTAQ oxidation was observed, and an anodic wave at +0.91 V was observed in oxidation of OTATQ due to it contains stronger electron withdrawing unit in which contain thiadiazolo structure. The UV–vis-NIR spectra analysis revealed that the POTAQ film has two absorbance bands centered at 694 nm and longer than 1,600 nm and the POTATQ film has an absorbance at 1,014 nm, respectively. The band gaps of these polymers, defined as the onset of the absorption band at 694 nm for POTATQ and the absorption band at 1,014 nm for POTATQ, were determined as 1.06 eV for POTAQ and as 0.76 eV for POTATQ. The electrochromic results showed that the two polymer films revealed about 30 % optical contrast in the NIR region with low response time (5 s for POTAQ and 10 s for POTATQ).