Synthesis, characterization, and optical and electrochemical properties of new 2,1,3-benzoselenadiazole-based CT-type copolymers

New alternating donor-acceptor charge-transfer (CT)-type copolymers consisting of didodecyloxy-p-phenylene (Ph), N-(4-dodecyloxyphenyl)carbazole (Cz), or N-hexyldiphenylamine (Da) unit (pi-electron donor) and 2,1,3-benzoselenadiazole (BSe) unit ( T-electron acceptor) were prepared by palladium-catalyzed Suzuki coupling reaction in 85-96% yields. The copolymers with the Ph and Cz units were soluble in common organic solvents and gave number-average molecular weights of 8300 and 6600, respectively, in GPC analysis; the copolymer with the Da unit was partly soluble in the solvents. The UV-vis absorption peak of the polymers appeared in the range of 420-530 nm in solutions and films, and the optical transition is considered to be accompanied by CT from the donor unit to the BSe unit. Quantum-chemical calculations of a trimeric model compound (Ph-BSe-Ph: 10) supported the notion that the optical activation of the copolymer involved the CT process. Cyclic voltammetry revealed that the copolymers were susceptible to both electrochemical oxidation and reduction, and they had a LUMO level ranging from -3.08 to -2.91 eV and a HOMO level ranging from -5.56 to -5.12 eV. Comparison of the electronic effect of the BSe unit with that of a 2,1,3-benzothiadiazole unit is discussed.