Nano-aggregates of furan-2-carbohydrazide derivatives displaying enhanced emission with a bathochromic shift

The non-fluorescent Schiff base compound C1 (N'-((4'-ethyl-3-hydroxy-[1,1'-biphenyl]-4-yl)methylene)furan-2-carbohydrazide) in organic solvent (e.g., THF) was found to produce yellow-green fluorescence emission upon addition of H₂O, and granular-shaped aggregates in a THF/H₂O mixed solution formed and exhibited obvious aggregation-induced emission (AIE). Especially its keto fluorescence band intensified dramatically, while the enol emission band remained almost unchanged. Hence, a change in fluorescence from no emission of light to emission of bright yellow-green light under a UV lamp was observed with the naked eye. In contrast, the reference compound C2 (N'-((4'-ethyl-3-methoxy-[1,1'-biphenyl]-4-yl)methylene)furan-2-carbohydrazide) showed no intensified fluorescence emission under the same experimental conditions. These results indicated the significant role played by intramolecular H-bonding in the formation of the C1 aggregates and the AIE process.