Experimental and Theoretical Study for Proton Transfer of Aggregated‐Induced Emission Active Fluorescent Schiff Bases.

In this paper, we studied the effect of increasing the conjugation in compound 3 on the proton transfer and aggregation‐induced emission properties. Compound 3 exhibited the dual absorption peak at 420 nm and 320 nm, which was redshifted by 50 nm compared to compound 2 (previous report). Compound 3 emits exhibited a peak at 530 nm with a Stokes' shift of 110 nm after photoexcitation at 420 nm. In a high polarity medium, the absorption and emission spectra of compound 3 showed redshifts of 50 nm and 20 nm, respectively. Further, compound 3 displayed the aggregation‐induced emission enhancement in THF/H2O (60 % v/v). Additionally, the proton transfer process in compounds 2 and 3 was evaluated through theoretical calculations via determining the relative free energies of possible tautomeric forms. It was determined that the small energy barriers for compound 2 in the S1 state suggested the presence of the proton transfer process; however, high energy barriers and high stabilization and Boltzmann population of 3.KK tautomeric form at S0 and S1 state for compound 3 discommoded the proton transfer process. Further, the aggregated form of compound 3 (20 μM; CH3OH/HEPES buffer (4 : 1; v/v) pH=7.04) was utilized to recognize Cu2+ ions with the lowest detection limit of 1.5 nM and Stern‐Volmer binding constant of 2.8×105 M−1. A noted decrease in the hydrodynamic size of compound 3 from 400 nm to 40 nm in the presence of Cu2+ ions confirmed the disaggregation with a decrease in emission intensity. Compound 3 was also employed as a Cu2+ ions recognizer in different collected samples with good percentage recovery. [ABSTRACT FROM AUTHOR]