Synthesis and optical properties of poly(p-phenylenevinylene)s bearing tetraphenylthiophene or dibenzothiophene moieties along the main chain

摘要

2,5-Bis(4-iodophenyl)-3,4-diphenylthiophene was synthesized by a four-step reaction starting from benzylchloride and sulfur. This reacted with 1,4-didodecyloxy-2,5-divinylbenzene to afford polymer P1. In addition, dibenzothiophene was brominated to give 2,8-dibromodibenzothiophene, that yielded by Heck coupling polymer P2. Both polymers are poly(p-phenylenevinylene) derivatives containing tetraphenylthiophene or dibenzothiophene moieties along the backbone. They dissolved readily in tetrahydrofuran and chloroform with glass-transition temperatures lower than 80 deg C. The solutions of polymers emitted greenish light with photoluminescence (PL) maximum at 460-480 nm. The PL quantum yields in solution were 0.24 for P1 and 0.52 for P2. Thin films of polymers emitted bluish-green light with PL maximum near 510nm and optical energy gap about 2.50eV. P1 displayed tower tendency to form aggregates than P2. The cyclic voltammograms of polymers showed an irreversible oxidation and no reduction peaks, suggesting that electron transport through the polymers was very poor. Both single and bilayer LEDs of P2 exhibited low current densities with turn-on voltage at 6-7 V, while the electroluminescence (EL) was not measurable.