Synthesis and properties of phenothiazylene vinylene and bithiophene-based copolymers for organic thin film transistors

A series of new phenothiazylene vinylene and thiophene copolymers (P1, P2, and P3) have been synthesized via Yamamoto and Stille coupling reactions. The number-averaged molecular weights (Mn) of P1, P2, and P3 were found to be 12,000, 10,000, and 8200, with polydispersity indices of 3.5, 1.4, and 1.6, respectively. The UV-visible absorption spectra of the polymers contain two strong absorption bands in the ranges 306-325 nm and 430-480 nm, which arise from the absorptions of the phenothiazine segments and the conjugated main chains respectively. Solution-processed field-effect transistors (FETs) fabricated with these polymers exhibit p-type organic thin film transistor characteristics. The field-effect mobilities for P1, P2, and P3 were measured to be 1.8 × 10−4, 5.7 × 10−4, and 2.5 × 10−7 cm2 V−1s−1, respectively, with the corresponding on/off ratios of 5 × 102, 1 × 104, and 5 × 102.