Julolidine-based Schiff's base as a Zn2+ chemosensor: experimental and theoretical study

Abstract

A novel julolidine-derived Schiff base (L₁) was synthesized through a facile one-step condensation reaction and evaluated for its potential as a fluorescent chemosensor. L₁ exhibited exceptional selectivity and sensitivity toward Zn²⁺ ions in an ethanolic medium, displaying a ‘turn-on’ fluorescence response with a significant blue shift in emission and a 12-fold enhancement in fluorescence intensity. The binding mechanism was investigated via DFT calculations, stacked NMR spectroscopy, and Job's plot analysis. The inhibition of ESIPT and the activation of CHEF pathways confirmed the proposed sensing mechanism. This process, coupled with increased molecular rigidity, also enhanced the fluorescence quantum yield from 0.00174 to 0.00230. The binding constant and detection limit for Zn²⁺ were determined to be 1.57 × 10⁷ M⁻¹ and 1.61 μM, respectively, with the DFT results aligning closely with experimental absorption data.