A highly selective fluorescent probe for Hg2+ based on a rhodamine–coumarin conjugate

A fluorescent probe 1 for Hg2+ based on a rhodamine–coumarin conjugate was designed and synthesized. Probe 1 exhibits high sensitivity and selectivity for sensing Hg2+, and about a 24-fold increase in fluorescence emission intensity is observed upon binding excess Hg2+ in 50% water/ethanol buffered at pH 7.24. The fluorescence response to Hg2+ is attributed to the 1:1 complex formation between probe 1 and Hg2+, which has been utilized as the basis for the selective detection of Hg2+. Besides, probe 1 was also found to show a reversible dual chromo- and fluorogenic response toward Hg2+ likely due to the chelation-induced ring opening of rhodamine spirolactam. The analytical performance characteristics of the proposed Hg2+-sensitive probe were investigated. The linear response range covers a concentration range of Hg2+ from 8.0 × 10−8 to 1.0 × 10−5 mol L−1 and the detection limit is 4.0 × 10−8 mol L−1. The determination of Hg2+ in both tap and river water samples displays satisfactory results.