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

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 cm 2 V −1 s −1 (average 0.64 cm 2 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 cm 2 V −1 s −1 , highest 0.55 cm 2 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.