Contorted tetrabenzoacenes of varied conjugation: charge transport study with single-crystal field-effect transistors

Abstract

A series of contorted and polyfused aromatic tetrabenzoacene derivatives differing in conjugation length were synthesized and characterized. X-ray diffraction revealed the contorted molecular shape, as well as the packing arrangement of these molecules. Thus unsubstituted tetrabenzoacenes showed a shifted or perfect face-to-face π-stacking depending on their conjugation length. The single crystals of these tetrabenzoacenes were used as conducting channels in fabricating field-effect transistors (SCFETs). Tetrabenzotetracene (TBT) exhibited the highest measured mobility, approaching 0.81 cm² V⁻¹ s⁻¹ (average 0.64 cm² V⁻¹ s⁻¹) among these molecules. In contrast, theoretical calculation showed that the tetrabenzooctacene (TBO) crystal has large-area, face-to-face π-packing, with the highest intermolecular coupling in the series. The lower charge mobility (average 0.32 cm² V⁻¹ s⁻¹, highest 0.55 cm² V⁻¹ s⁻¹) observed was rationalized as a result of possible involvement of delocalized polaron formation due to comparable electronic coupling and reorganization energy in TBO, as supported by the Monte Carlo simulation with this delocalized effect taken into account.