Electropolymerization of Bis(2-cyano-2-α-thienylethenyl)arylenes

The synthesis and the electrochemical studies of 1,3-bis(2-cyano-2-R-thienylethenyl)benzene (1), 1,4-bis(2-cyano-2-R-thienylethenyl)benzene (2), and 2,7-bis(2-cyano-2-R-thienylethenyl)biphenylene (3) are reported herein. While compound 2 could be reversibly reduced to form the corresponding dianion, compounds 1 and 3 show irreversible or quasireversible reductions in their cyclic voltammetric studies. We tentatively attribute the high reactivity of the dianions of 1 and 3 to their diradicaloid behavior. This explanation is further supported by PM3/RHF-PM3/UHF calculations. Compounds 1-3 could be irreversibly oxidized at the potential more positive than +1.3 V. Among these compounds, 3 shows the highest reactivity toward oxidative electropolymerization. The resulting polymer film is relatively stable and electroactive. Although polymeric films of compounds 1 and 2 could be formed at higher monomer concentrations, the films are unstable toward electrochemical oxidation. UV-vis analyses of the polymeric films reveal that electropolymerization of 2 is quenched at the early stage of the polymerization, resulting in significant amounts of oligomers in the matrix. However, biphenylene containing monomer 3 could be smoothly converted to highly conjugated polymers under electrochemical oxidation.