A Reaction-Based ESIPT Fluorescent Probe for the Detection of Hg²⁺ with Large Stokes Shift

A novel reaction-based fluorescent probe 1 for Hg²⁺ was designed and synthesized. 1 was almost nonfluoresent due to inhibition of the ESIPT process between hydroxy group and imid carbonyl oxygen by diphenylphosphinothioate group. After reacting with Hg²⁺, the fluorescence intensity of 1 exhibited significant enhancement owing to recovery of the ESIPT process via Hg²⁺-promoted desulfurization-hydrolysis of the diphenylphosphinothioate moiety and cleavage of the P-O bond. 1 not only showed rapid response, high sensitivity, excellent selectivity for Hg²⁺ over other metal ions, but also could detect Hg²⁺ with large Stokes shift (165 nm), which was attributed to the ESIPT process. Moreover, the reaction mechanism was fully validated by absorption spectra, fluorescence spectra, fluorescence color as well as ESI-MS analysis.