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The o-carborane-based π-conjugated compound, benzocarborano- 2,1-b:3,4-b'dithiophene was synthesized. Its crystal structure revealed high coplanarity for the two thiophene rings of the 2,2'-bithiophene skeleton, which is fixed in the cisoid structure by the o-carborane unit. Theoretical calculations indicated non-aromaticity for its center C(6) ring moiety as well as decreased HOMO and LUMO levels. The o-carborane moiety provides an electron-withdrawing character to the 2,2'-bithiophene unit through an inductive effect.
Morisaki et al. (Tue,) studied this question.