An excited-state intramolecular proton transfer-based probe for the discrimination of thiophenols over aliphatic thiols

Abstract

The development of probes for the rapid, selective, and sensitive detection of thiophenols is of great importance, due to the toxicity of thiophenols and their derivatives in the environment. In this work, a new excited-state intramolecular proton transfer (ESIPT)-based probe for the discrimination detection of thiophenols over aliphatic thiols was developed, in which 2-(1-(4-methoxyphenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenol (DIP) acted as the fluorophore and the strongly electron-withdrawing 2,4-dinitrobenzene sulfonyl ester group acted as the recognition unit. The non-fluorescent probe molecule can release the corresponding fluorescent fluorophore (DIP) through aromatic nucleophilic substitution (S_NAr) by thiolate anions from thiophenols. The fluorophore displayed a large Stokes shift (>170 nm) and the probe showed a very fast response (within 1 min) to thiophenols. Quantitative detection of thiophenol with a linear response from 0.1 μM to 7 μM and a detection limit of 0.189 μM was achieved. This probe shows high selectivity to thiophenols over aliphatic thiols and other nucleophiles and it can be used to detect thiophenol in real water samples with good recovery. The probe is also a useful fluorescent probe for detecting thiophenols in living cells.