Electronic Alteration on Oligothiophenes by o-Carborane: Electron Acceptor Character of o-Carborane in Oligothiophene Frameworks with Dicyano-Vinyl End-On Group

We studied electronic change in oligothiophenes by employing o-carborane into a molecular array in which one or both end(s) were substituted by electron-withdrawing dicyano-vinyl group(s). Depending on mono- or bis-substitution at the o-carborane, a series of linear A1-D-A2 (1a-1c) or V-shaped A1-D-A2-D-A1 (2a-2c) oligothiophene chain structures of variable length were prepared; A1, D, and A2, represent dicyano-vinyl, oligothiophenyl, and o-carboranyl groups, respectively. Among this series, 2a shows strong electron-acceptor capability of o-carborane comparable to that of the dicyano-vinyl substituent, which can be elaborated by a conformational effect driven by cage σ*-π* interaction. As a result, electronic communications between o-carborane and dicyano-vinyl groups are successfully achieved in 2a.