Transport Properties of Molecular Conductors (BSBS)2XF6 (X = As, Sb, and Ta): Investigation of Intermolecular Transfer Integrals in the Radical-Cationic State of Benzothienobenzothiophene-Type Semiconductors

[1]­Benzoseleno­[3,2-b]­benzoselenophene (BSBS) derivatives are known as high-performance transistor materials. Novel and highly conductive charge-transfer (CT) complexes, (BSBS)2XF6 (X = As and Sb), have been prepared, and their transport properties are investigated. At room temperature, these complexes exhibit conductivities larger than 600 S cm–1. The chemical pressure effect originating from the counter anion size is estimated to be 0.3 kbar. The thermoelectric (TE) power is 15–17 μV K–1, demonstrating that the BSBS complexes have remarkably large transfer integrals of 310 meV, as observed in the highly conductive benzothienobenzothiophene (BTBT) complexes. From both molecular orbital calculations and experiments, it is demonstrated that the BTBT skeleton has the property of forming a very large energy bandwidth. The TE power of metallic CT complexes based on organic transistor molecules is useful for experimentally determining the intermolecular transfer integrals of charged semiconductor molecules.