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

We studied electronic change in oligothiophenes by employing <i>o</i>-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 <i>o</i>-carborane, a series of linear A<sub>1</sub>-D-A<sub>2</sub> (<b>1a</b>–<b>1c</b>) or V-shaped A<sub>1</sub>-D-A<sub>2</sub>-D-A<sub>1</sub> <b>(2a</b>–<b>2c</b>) oligothiophene chain structures of variable length were prepared; A<sub>1</sub>, D, and A<sub>2</sub>, represent dicyano-vinyl, oligothiophenyl, and <i>o</i>-carboranyl groups, respectively. Among this series, <b>2a</b> shows strong electron-acceptor capability of <i>o</i>-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 <i>o</i>-carborane and dicyano-vinyl groups are successfully achieved in <b>2a</b>.