Design strategy for air-stable organic semiconductors applicable to high-performance field-effect transistors

Electronic structure cf air-stable, high-performance organic field-effect transistor (OFET) material, 2,7-diphencyl[1]benzothieno[3,2-b] benzothiophene (DPh-BTBT), was discussed based on the molecular orbital calculations. It was suggested that the stability is originated from relatively low-lying HOMO level, despite the fact that the molecule contains highly pi-extended aromatic core ([I]benzothieno[3,2-b] benzothiophene, BTBT) with four fused aromatic rings like naphthacene. This is rationalized by the consideration that the BTBT core is not isoelectronic with naphthacene but with chrysene, a cata-condensed phene with four benzene rings. It is well known that the acene-type compound is unstable among its structural isomers with the same number of benzene rings. Therefore, polycyclic aromatic compounds possessing the phene-substructure will be good candidates for stable organic semiconductors. Considering synthetic easiness. we suggest that the BTBT-substruture is the molecular structure of choice for developing air-stable organic semiconductors. (C) 2007 NIMS and Elsevier Ltd. All rights reserved.