Extended conjugated borenium dimers via late stage functionalization of air-stable borepinium ions.

Applications of highly electron-deficient organoborenium ions in conjugated materials remain scarce due to their low stability toward air and moisture. We report here the preparation of benzo[d]dithieno[b,f]borepinium ions as air-stable π-conjugated heterocycles and their conversion into the first dimeric borenium cations, which exhibit very low lying LUMOs and enhanced fluorescence as a result of extended conjugation.