Synthesis, optical, and electrochemical properties of novel copolymers on the basis of benzothiadiazole and electron-rich arene units

Novel alternating conjugated copolymers (P1-P6) consisting of an electron-deficient benzothiadiazole and a variety of electron-rich thiophene-arene-thiophene units were synthesized by palladium-catalyzed polycondensations (Stille and Suzuki reactions), aiming at processable materials with a reduced optical band gap. The structures of P1-P6 were confirmed by 1H NMR and 13C NMR, and their mol. wts. were detd. by size exclusion chromatog. In the Suzuki polycondensation, the role of the catalyst [Pd(PPh3)4 and Pd(OAc)2] on the resulting mol. wt. was investigated. Pd(OAc)2 enhances the mol. wt. of the polymers for both thiophene and phenylene bis-boronic esters as compared with Pd(PPh3)4. The optical properties of the polymers were examd. in soln. and the solid state. The polymers with n-octyl substituents (P1, P4, P5, and P6) on the thiophene rings possessed less-planar structures as a result of torsional steric hindrance, and their absorption spectra appeared blue-shifted as compared with their unsubstituted analogs (P2 and P3). The electrochem. properties of the polymers were studied using cyclic voltammetry. Although the alkyl substitution affects the oxidn. potential, only marginal differences in the redn. potentials were obsd. [on SciFinder (R)