A FRET-based ratiometric fluorescent probe with large pseudo-stokes for the detection of mercury ion based on xanthene and naphthalimide fluorophores

A novel naphthalimide-xanthene probe for detecting Hg 2+ was designed based on the FRET mechanism, and its detailed mechanism was further studied. • A colorimetric and ratiometric fluorescent probe for detecting Hg 2+ based on naphthimide and xanthene was synthesized. • The response time of Hg 2+ detection was less than 30 s and the fluorescence emission peak was red-shifted by 130 nm. • The detection mechanism for Hg 2+ had been verified by ESI-MS, NMR and HPLC spectra. In this work, a novel colorimetric and ratiometric fluorescent probe ( R1 ) for detecting Hg 2+ based on xanthene and naphthimide groups via the fluorescence resonance energy transfer (FRET) mechanism was designed and synthesized. In the CH 3 CN/H 2 O (1/1, v/v) system, the probe R1 showed ratiometric fluorescent responsiveness to Hg 2+ with the characteristics of rapid response time (less than 30 s), high selectivity and excellent anti-interference ability, meanwhile, the fluorescence color changed from cyan to orange and the solution color changed from colorless to pink by naked-eye. Based on fluorescence and UV/vis measurements, the limit of detection (LOD) was calculated to be 1.14 μM and 0.17 μM, respectively. Furthermore, the possible mechanism for the detection of Hg 2+ of probe R1 was verified by using ESI-MS, 1 H NMR and HPLC spectra.