Highly Polarized Benzo[k]fluoranthene Imide Derivatives: Large Solvatofluorochromism, Dual Fluorescence and Aggregation Induced Emission Associated with Excited-State Intramolecular Charge Transfer

The highly conjugated imides, 9-diphenyl-aminobenzo[k]fluoranthene imide and N-phenylcarbazo[2,3-k]fluoranthene imide, were produced by Buchwald-Hartwig reaction of N-octyl-9,10-dibromobenzo[k]fluoranthene imide with diphenylamine. In a similar manner, reaction of the N-ethylhexyl-9,10-dibromo derivative with carbazole leads to formation of 9-(N-carbazoyl)benzo[k]fluoranthene imide. All the benzo[k]fluoranthene imide (BFI) derivatives in solution show remarkable solvatofluorochromism. Diphenylamino and 9-(N-carbazoyl) derivatives, having twisted structures, exhibit fluorescence bands at short wavelengths in highly polar solvents, and they emit dual fluorescence in acetone. Moreover, the 9-(N-carbazoyl) derivative displays aggregation-induced emission in highly aqueous acetone solutions. The results of density functional theory calculations demonstrate that a considerable spatial separation exists between the HOMO and LUMO coefficients of the N-arylamine substituted BFIs. The results indicate that the ground-to-excited state transitions of these compounds have intramolecular charge transfer character.