Smartphone‐Assisted Quinoline‐Based Chromogenic Probe for the Selective Detection of Hg2+ in Protic Media

Abstract High selectivity and sensitivity detection of Hg 2+ in aqueous environment by the naked‐eye has always been a challenge. In this paper, a simple ligand based on 2‐(hydroxymethyl)quinolin‐8‐ol ( L ) was synthesized and its structure was confirmed by NMR, IR and mass analysis. The probe L showed distinct colorimetric upon interaction with Hg 2+ in CH 3 OH‐H 2 O (8 : 2, v/v) media. The ligand L exhibit unique absorbance band at 243 nm due to ligand‐to‐ligand charge transfer (LLCT). Upon interaction with Hg 2+ , the L formed new UV‐Vis bands at 269 and 316 nm due to ligand‐to‐metal charge transitions (LMCT). The UV‐Vis spectral studies indicate the formation of a 1 : 1 host‐guest complex between the L and Hg 2+ with an association constant of 8.6×10 4 M −1 . The ligand L can work in the pH range of 3–8 without interfering with other competing ions. The detection limit of Hg 2+ can reach a concentration of as low as 0.13 μM (2.6 ppb) with high selectivity, even in a solution containing diverse metal ions. Besides, the selective colour change of L with Hg 2+ was integrated with smartphone to monitor the change in RGB tool and test paper kit. The binding mechanism of L with Hg 2+ was studied by using 1 H NMR, SEM and TDDFT analysis. Overall, ligand L demonstrates a promising and potential for the detection of toxic contaminate in aqueous environment.