Effect of electron-withdrawing side chain modifications on the optical properties of thiophene–quinoxaline acceptor based polymers

Abstract

Four new thiophene–quinoxaline acceptor based polymers have been synthesized. The parent thiophene–quinoxaline acceptor based copolymer was modified by introducing different electron-withdrawing groups adjacent to the thiophene side group. The effect on the physical, electrochemical and optical properties of the polymer series is discussed with respect to the parent thiophene–quinoxaline acceptor based polymer. The side chain carbonyl from one modified monomer could conveniently be transformed to either a difluoromethylene or an -ylidene malononitrile group via carbonyl transformations. For all polymers incorporating an electron-withdrawing side group both the HOMO and especially the LUMO were significantly shifted away from vacuum while all exhibit enhanced light harvesting ability. Especially the incorporation of an -ylidine malononitrile side group increases both the spectral coverage and absorption coefficient. Incorporation of a difluoromethylene side group resulted in a twofold increase of the molecular weight compared to the parent polymer structure.