A novel phenanthroline[9,10-d] imidazole-based fluorescent sensor for Hg2+ with “turn-on” fluorescence response

A phenanthroline[9,10-d] imidazole-based fluorescent sensor was synthesized for Hg2+, accompanied by change of fluorescence from null to blue. [Display omitted] •A novel phenimidazole fluorescence sensor compound 1 was developed.•The sensor compound 1 exhibited fluorescent response to Hg2+.•Low cost, high sensitivity, superior selectivity, and low detection limit for Hg2+.•The sensor compound 1 had advantages in detecting Hg2+ in practical applications. Herein, a phenanthro[9,10-d] imidazole Schiff based “turn-on” fluorescence sensor (compound 1) was synthesized by 4-hydroxy-3-nitrobenzaldehyde and 9,10-phenanthrenequinone. In DMF/PBS buffer solution (1:4, v/v, pH 7.4), compound 1 responsed to Hg2+ with high sensitivity (detection limit was 45.76 nM) and rapid response (completed within 5 s), accompanied by the fluorescence change from null to blue. The binding ratio of compound 1 to Hg2+ was 1:1, and the binding constant was 2.933 × 106 M−1. Through detailed analysis of 1H–1H COSY and 1H–13C HSQC spectra, we proposed the possible fluorescence emission mechanism of compound 1 and Hg2+, and verified the recognition mechanism of compound 1 through density functional theory (DFT) calculation. Compound 1 was successfully used to detect Hg2+ in actual water samples, the recovery was 91 %–106 %, and the relative standard deviation (R.S.D.) was less than 2.5 %, which provided possibility for compound 1 to be used as a sensor in environmental research.