An ICT-based highly fluorescent isoquinoline scaffold for selective Hg(II) detection in real-water samples:...

Selective detection and quantification of Hg²⁺ ions is crucial to minimize health and environmental risks. Fluorescent organic small-molecule probes have been expeditiously utilized owing to their unique set of improved properties. However, isoquinoline core has not been extensively explored as a fluorescence platform partly due to synthetic challenges. Herein, a serendipitously discovered synthetic route to access a small yet highly functionalized novel isoquinoline-based probe, IQ is reported. The synthesis is achieved through the in-situ generation of ammonia, followed by intermolecular [5C + 1 N] aza-annulation reaction with a ketendithioacetal-based precursor, P-IQ. IQ displayed excellent recognition ability towards Hg²⁺ ions in H₂O:ACN (99:1, v/v) via ICT-off fluorescent quenching behavior. Comparative FT-IR, ¹H/¹³C NMR, mass spectral studies, and DFT analyses were carried out to validate the suggested mechanisms. Reversible studies confirm the secondary recognition effect of in-situ generated (IQ + Hg²⁺) complex on cysteine. The binding constant and LOD were estimated to be 3.7 × 10⁴ M^-1 and 0.86 µM, respectively. Further, IQ was utilized to evaluate the mercury ion content in real water samples demonstrating its effectiveness in water quality monitoring. The practical utility of IQ was further explored by developing TLC strips, Whatman filter-paper strips, and a low-cost, portable Arduino-based platform. Arduino microcontroller is interfaced with an RGB sensor to detect color changes and quantify mercury concentration w.r.t. RGB values.