Energy Level Tuning of Polythiophene Derivative by Click Chemistry-Type Postfunctionalization of Side-Chain Alkynes

A polythiophene derivative substituted with electron-rich alkynes as a side chain was synthesized using the Suzuki polycondensation reaction. The electron-rich alkynes underwent the click chemistry-type quantitative addition reaction with strong acceptor molecules, such as tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ), resulting in the formation of donor-acceptor chromophores. All polymers showed excellent solubilities in the common organic solvents as well as good thermal stabilities with their 5% decomposition temperatures exceeding 230 degrees C. The TCNE-/TCNQ-adducted polymers displayed well-defined charge-transfer (CT) bands in the low energy region. The CT energy of the TCNE-adducted polymer was 2.56 eV (484 nm), which was much greater than that of the TCNQ-adducted polymer [1.65 eV (750 nm)]. This result was supported by the electrochemical measurements. The electrochemical band gaps of the TCNE-adducted polymers were much greater than those of the corresponding TCNQ-adducted polymers. Furthermore, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, determined from the first oxidation and first reduction peak potentials, respectively, decreased with the increasing acceptor addition amount. All these results suggested that the energy levels of the polythiophene derivative can be tuned by varying the species and amount of the acceptor molecules using this postfunctionalization method. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 225-233, 2011