Synthesis of 2,7-dioctylbiphenylenodithiophenes for use as organic semiconducting materials in solution-processed organic thin-film transistors

Abstract

A synthetic route to 2,7-dialkylbiphenylenodithiophenes was developed and their potential as a new π-core system for organic semiconductors was investigated. The semiconductors 2,7-dioctylbiphenyleno[2,1-b:6,5-b′]dithiophene (C8-B1-BPDT), 2,7-dioctylbiphenyleno[1,2-b:5,6-b′]dithiophene (C8-B2-BPDT), and 2,7-dioctylbiphenyleno[2,3-b:6,7-b′]dithiophene (C8-L-BPDT) were synthesized from dihalobiphenylenes. Structural analysis by single-crystal X-ray crystallography revealed that C8-B1-BPDT adopts a herringbone motif whereas C8-B2-BPDT has an interdigitated structure. C8-B1-BPDT and C8-B2-BPDT displayed high solubilities of more than 0.80 wt% in toluene. In contrast, C8-L-BPDT exhibited a low solubility of 0.060 wt% in toluene at room temperature. Although C8-B2-BPDT formed noncontinuous films on a parylene-C dielectric layer by solution deposition, films of C8-B1-BPDT covered the whole area of the parylene-C layer. Bottom-contact bottom-gate thin-film transistors with a mobility of 0.58 cm² V⁻¹ s⁻¹ were fabricated by drop casting of a solution of C8-B1-BPDT.