ELECTRICALLY CONDUCTING POLYMERS CONTAINING ALTERNATING SUBSTITUTED PHENYLENE AND BITHIOPHENE REPEAT UNITS

Poly(di-2-thienylphenylene) (2a), poly(di-2-thienyl-2,5-dimethylphenylene) (2b), and poly-(di-2-thienyl-2,5-dimethoxyphenylene (2c) have been prepared to examine the effect of substitution on polymer structure and ultimately their physical, optical, electrical, and electrochemical properties. The polymers contain no configurational isomerism due to head to head linkages with fully conjugated structures exclusively composed of alpha-thienyl couplings. Electrical conductivities for pressed pellets of 2c of 2-OMEGA-1 cm-1 have been measured, while powders of 2a and 2b exhibit conductivities of 0.52 and 10(-6) OMEGA-1 cm-1, respectively. Electronic band gaps (E(g)) of 2.2, 2.7, and 2.2 eV are found for polymers 2a-c, respectively, which are in close correlation with theoretically calculated values of 2.0, 2.6, and 2.2 eV. All of the polymers are electroactive with typical electronic absorption spectral signatures of bipolarons, though 2b is significantly more difficult to oxidatively dope. Correlation of calculated minimum energy conformations, barriers to rotation, and band structures with experimental results indicates that the methyl-substituted polymer (2b), with a high barrier to rotation (i.e., planarity), exhibits a high band gap, narrow bandwidth, and ultimately low electrical conductivity. Conversely, the alkoxy-substituted polymer (2c) exhibits a low barrier to rotation, wider bandwidth and energy gap, comparable to the unsubstituted polymer (2a), and ultimately a high conductivity in the doped state. es that the methyl-substituted polymer (2b), with a high barrier to rotation (i.e., planarity), exhibits a high band gap, narrow bandwidth, and ultimately low electrical conductivity. Conversely, the alkoxy-substituted polymer (2c) exhibits a low barrier to rotation, wider bandwidth and energy gap, comparable to the unsubstituted polymer (2a), and ultimately a high conductivity in the doped state.