Synthesis, structural characterization, and unusual field-effect behavior of organic transistor semiconductor oligomers: Inferiority of oxadiazole compared with other electron-withdrawing subunits

A new series of heterocyclic oligomers based on the 1,3,4-oxadiazole ring were synthesized. Other electron-deficient cores (fluorenone and fumaronitrile) were introduced to investigate the oligomers as n-channel materials. The physical properties, thin film morphologies, and field-effect transistor characteristics of the oligomers were evaluated. Thin films were deposited at different substrate temperatures and on variously coated Si/Si0₂ for device optimization. Contrary to our expectations, the thin film devices of 4 revealed p-channel behavior, and the average hole mobility was 0.14 cm ² V^-1 s^-1 (maximum value 0.18 cm² V^-1 s^-1). Compound 11 is the first example of an oxadiazole-containing organic semiconductor (OSC) oligomer in an n-channel organic field-effect transistor (OFET) and shows moderate mobilities. Non- oxadiazole-containing oligomers 9 and 12 showed n-channel OFET behavior on hexamethyldisilazane- treated and Cytop spin-coated Si0₂ in vacuum. These are the first fluorenone- and fumaronitrile-based n-OSCs demonstrated in transistors. However, oxadiazole-core materials 14 and 16 were inactive in transistor devices.