Ortho-Vanillin-based fluorescent sensor with ESIPT characteristics for selective detection of Al(III) in aqueous solutions and its application for plant and live-cell imaging.

• A VN62 fluorescent sensor with ESIPT propertywas designed, synthesized and characterized. • VN62 sensor exhibited rapid and stable detection of Al3+ with a remarkable fluorescence enhancement in aqueous solution. • The sensing mechanism of VN62 sensorto Al3+ wasreasonably speculated based on experimental results and theoretical calculations. • VN62 sensor was capable of recognizing Al3+ by test strips and imaging Al3+in plants and living cells. A new acylhydrazone fluorescent sensor (VN62) with excited intramolecular proton transfer (ESIPT) characteristics has been designed and synthesized through condensation of o -vanillin with 6‑hydroxy-2-naphthoic hydrazide for selective detection of Al3+ in aqueous medium. The structure of the VN62 sensor was characterized by various techniques such as 1H and 13C NMR and mass spectrometry, and also confirmed by single crystal X-ray diffraction. The VN62 sensor showed a remarkable fluorescence enhancement response to Al3+ over a broad pH range in a nearly 100 % aqueous solution without interference by most of tested metal ions and anions. Through fluorescence titration and a Job's plot experiment, the binding stoichiometry of VN62 with Al3+ was found to be 1:1. The limit of detection of VN62 toward Al3+ was determined as 39.6 nM and the binding constant was 2.66 × 104 M−1. Comprehensive analyses by HR-MS, 1H NMR and density functional theory calculations illustrated that the VN62 sensor coordinated with Al3+, forming a stable trigonal bipyramid structure complex, which blocked the ESIPT and photoinduced electron transfer processes and simultaneously promoted an intramolecular charge transfer process, thereby leading to strong cyan fluorescence. Moreover, VN62 -loaded test strips were successfully applied for rapid and visual detection of Al3+. Furthermore, the VN62 sensor was used to visualize Al3+in plants and live cells. The results indicated that the VN62 sensor has great potential for detecting Al3+in biological systems. [Display omitted] [ABSTRACT FROM AUTHOR]