Thiophene-phenylene and Thiophene-thiazole Oligomeric Semiconductors with High Field-Effect Transistor On/Off Ratios

A series of thiophene-containing oligomers less electron rich than alpha-6T was synthesized and the thin film morphologies and field-effect transistor (FET) characteristics of the oligomers were evaluated. Phenyl and thiazole rings were included in many of the oligomers, and a new synthesis of perfluoroalkylmethyl-terminated oligomers was developed. Desirably low off currents were associated with calculated highest occupied molecular orbital (HOMO) energies above ca 5.0 eV. Some of the oligomers displayed mobilities above 0.01 cm sup 2 / Vs, but there was no correlation of mobility with calculated orbital energies and some compounds with seemingly continuous morphologies had low mobilities nonetheless. One component 1,4-bis(5'-hexyl-1,1'-bithiophen-5-yl)benzene, showed promising behavior as a solution-deposited semiconductor, with mobility up to 0.02 cm sup 2 V/s and on/off ratio up to 20,000.