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.
Electropolymerization of'pyrrole in aqueous solution is monitored by electrochemical quartz crystal microbalance (EQCM) during potential scan. Tbe film formation process on the electrode is reflected by the frequency decrease for tbe quartz oscillator as a function of time. Tbe film growth rate is greatly enhanced in the presence of iron(III) meso-tetrakis(3-sulfonatomesilyl)porpbyrin, which carries 3-of charge. The metalloporphyrin is trapped and remains intact in the polypyrrole films. The ion transport property through the iron porphyrinlpolypyrrole film is the reverse of that for pure polypyrrole. Electroreduction of dioxygen and electrooxidation of alkenes are parallel to those in the solution state.
EXPERIMENTAL SECTION Reference 1Oscillator JĨ
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