Development of a novel isophorone-derived near-infrared fluorescent probe for specific and visual detection of Pb2+: Theoretical, practical and bioimaging investigations

The development of specific and visually detectable fluorophores for the accurate and rapid Pb²⁺ recognization is crucial. In this study, we introduced a novel isophorone-derived fluorescent probe, (E)-2-(3-(3-formyl-4-hydroxystyryl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (YSQ), rationally designed for prompt and high-quality Pb²⁺ detection. YSQ demonstrated noticeable red emitting fluorescence enhancement upon Pb²⁺ interactions (upon binding, τ_avg 16.7 ns, Φ 12 %) with visible color changes discernible to the naked eye in MeOH/H₂O (v/v 9/1, pH 7.4, 0.2 mM). The probe YSQ achieved a quite low detection limit (LOD) of 18 nM and a high association constant of 2.93 × 10⁵ M⁻¹ towards Pb²⁺ using fluorescence titration. We proposed a binding mechanism of YSQ with Pb²⁺ ions, supported by the density functional theory (DFT/TD-DFT), ¹H NMR titration experiments, IR and HRMS analysis. In addition, a simple and affordable smartphone-supported specific Pb²⁺ detection technique was developed with visible color changes. Furthermore, this NIR emissive properties of YSQ offered broad potential applications in actual water sample and solid analysis, bio-imaging and test strips.