Pyridoxal derived AIEgen as a fluorescent pH sensor

The pH plays a foremost role in many biological and chemical processes, so their determination is very important. In this manuscript, an easy-to-prepare pyridoxal derived Schiff base L was investigated for the fluorescent sensing of pH. The weakly emissive L in DMSO turned to red emissive L with the increase in the poor solvent fraction in DMSO because of the combined effects of the aggregation-induced emission (AIE) and excited-state intramolecular proton-transfer (ESIPT). The formation of needle-like self-aggregates of L was examined by SEM analyses. Also, the tendency to form self-aggregates was investigated by DFT calculations. The self-aggregates of L in mixed DMSO:HEPES medium containing 95% HEPES was applied for the fluorescent sensing of pH. The red-emissive self-aggregates of L in the physiological pH turned to green emissive due to the deprotonation of pyridoxal-OH. The fluorescence titration data at different pH was analysed to estimate a pKa value of 9.08 for the pyridoxal-OH.