Selective Recognition of Fluoride by using a Benzobisimidazolium Derivative through Aggregation‐Induced Fluorescence

A new benzobisimidazolium derivative (1) bearing four naphthalene moieties was synthesized and demonstrated as an F(−) ion‐selective fluorescent chemosensor. The fluorescence of 1 in acetonitrile (CH(3)CN) is significantly stronger with F(−) and acetate (CH(3)CO(2) (−)), but not with other anions (Cl(−), Br(−), I(−), HSO(4) (−), and H(2)PO(4) (−)). The fluorescence of 1 is enhanced selectively with F(−) in the presence of a small amount of water. Our DFT calculations indicate that the electrostatic interactions between the positively charged benzobisimidazolium moieties and F(−) play an important role in the formation of stable aggregates. The formation of stable aggregates of 1 with F(−) in CH(3)CN is a key step for the selective sensing of F(−), and the fluorescence of the aggregates is further enhanced in a mixture of 95 % CH(3)CN and 5 % water, which can be attributed to the aggregation‐induced emission.