title: Low bandgap polymers by copolymerization of thiophene with benzothiadiazole.
abstract: Three low bandgap copolymers of thiophene and benzothiadiazole with electron-donating and electron-withdrawing substituents, P1, P2, and P3, have been synthesized by Pd-catalyzed Stille-coupling. Electronic energy levels of the polymers are estimated by cyclic voltammetry. The polymer films show a broad absorption band in the wavelength range from 300 to 750 nm. Among the polymers, the polymer that contains the 5,6-dinitrobenzothiadiazole unit, P3, possesses the smallest bandgap of 1.55 eV calculated from its absorption band-edge at ≈800 nm. With the increase of the electron-withdrawing ability of the substituents on the benzothiadiazole unit, the energy bandgap of the polymers decreased in the order P1 > P2 > P3. The results indicate that stronger electron-withdrawing substituents on the acceptor unit can effectively decrease the bandgap of the polymers.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China; Graduate University of Chinese Academy of Sciences, Beijing 100039, P. R. China.
authors.forename: Youjun
authors.initials: Y
authors.lastname: He
authors.forename: Xiang
authors.initials: X
authors.lastname: Wang
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.forename: Yongfang
authors.initials: Y
authors.lastname: Li