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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.

We report a p-π* conjugated organic molecule based on triarylborane as n-type organic semiconductor with unique alcohol solubility. Its favorable alcohol solubility even in the absence of polar side chains is mainly due to the large dipole moment and enhanced flexibility of the conjugated backbone once the boron atom is embedded. The p-π* conjugation directly affects the electronic structure as the LUMO is fully delocalized, including the boron atom, whereas the HOMO has the boron atom residing on a node. As a result, the molecule exhibits low-lying LUMO/HOMO energy levels of −3.61 eV/−5.73 eV paired with a good electron mobility of 1.37 × 10 −5 cm 2 V −1 s −1 . We further demonstrate its application as an electron acceptor in alcohol-processed organic solar cells (OSCs). To our best knowledge, this p-π* conjugated molecule is the first alcohol-processable non-fullerene electron acceptor, a feature that is in strong demand for environmentally friendly processing of OSCs.