Multiple-color aggregation-induced emission (AIE) molecules: pH-responsive mechanism and fluorescence properties

A series of naphthalene-based Schiff base derivatives (L1-3) were successfully prepared. The Schiff base derivatives exhibit typical aggregation-induced emission (AIE) properties with various fluorescence emissions and pH responses in an alkaline environment. Through density functional theory (DFT) calculations, it is found that the electronegativity of the L1-3 changes with the change of the substituents on the 2-aminopyridine, which results in the L1-3 exhibiting multiple-color emission from green to orange. In addition, all naphthalene-based Schiff base derivatives exhibit green fluorescence emission under alkaline conditions. This is due to the intramolecular charge transfer (ICT) mechanism of the L1-3 which makes the L1-3 have a pH-response under alkaline conditions (pH at 7.0–12.0). The derivatives L1-3 exhibit unique optical properties, which indicated their potential applications in the field of optics and pH sensing materials.