Electrical and Optical Properties of Conducting Polymer with Quinoid Structure

Poly[α-(bithiophene-5,5'-diyl)-(p-(heptyloxy)benzylidene)-co-(α-bithiophene quinodimethane-5,5'-diyl)] (PBTHBQ), which is obtained from precursor poly[α-(bithiophene-5,5'-diyl)-(p-(heptyloxy)benzylidene)] (PBTHB) by oxidative dehydrogenation with 2,3-dichloro-5,6-dicyano-p-benzoquinone and contains alternating aromatic and quinoid thiophene rings in its main chain, has an optical absorption edge at about 1.4 eV, while the band gap of PBTHBQ was evaluated to be about 2.6 eV from the short-circuited photocurrent spectrum. The electrochemical and optical properties of PBTHBQ and PBTHB have been investigated by cyclic voltammetry, in situ optical absorption spectroscopy, photoconduction spectra measurements and electron spin resonance measurements. From these experimental results, electronic energy states of PBTHBQ and PBTHB were estimated. PBTHBQ was also found to be made from PBTHB by an electrochemical cycle.