Fluorescence Properties of Simple N-Substituted Aldimines with a B−N Interaction and Their Fluorescence Quenching by a Cyanide Ion

N-Aryl, N-alkyl, N-alkoxy, and N-amino derivatives of 2-[bis(pentafluorophenyl)boryl]benzylideneamine were synthesized by the condensation reactions of 2-[bis(pentafluorophenyl)boryl]benzaldehyde with the corresponding amines. Their structures were investigated by NMR and X-ray crystallographic analysis. Their properties were investigated by UV−vis and fluorescence spectroscopy. The boryl-substituted N-arylimines show blue or green fluorescence in hexane at room temperature, and their fluorescence efficiency is much higher than that of N-benzylideneaniline. In particular, the boryl-substituted N-(4-dimethylaminophenyl)imine showed strong green emissions with at least 7000 times higher fluorescence quantum yield (0.73) compared with that of N-benzylideneaniline. The boryl-substituted N-(1-indolyl)- and N-(9-carbazolyl)imines showed dual emissions, one of which was assignable as arising from the lowest singlet excited state and the other from the local excited state of the substituent on the imine nitrogen. The fluorescent properties of the boryl-substituted N-butyl- and N-methoxyimines were also investigated. Reactions of the N-arylimine derivatives with cyanide ion gave the corresponding cyanide adducts and quenched the fluorescence, indicating that these 2-[bis(pentafluorophenyl)boryl]benzylideneamine derivatives have a potential as a cyanide ion sensor.