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.