Comparative study of thioacetal and thiocarbonate recognition motifs in a dihydroxanthene fluorescent scaffold for Hg2+ sensing

Direct comparison of Hg 2+ recognition motifs on a unified DHX scaffold. • Thioacetal and thiocarbonate motifs showed distinct sensing characteristics. • DHX-DT provided higher sensitivity with a detection limit of 7.0 nM. • DHX-PTC afforded rapid Hg 2+ detection, reaching equilibrium in 3 min. Two structurally analogous probes, DHX-DT and DHX-PTC , were rationally designed by incorporating a thioacetal group and a phenyl thiocarbonate group, respectively, into the dihydroxanthene (DHX) framework. Upon Hg 2+ -triggered desulfurization, both probes were converted into the common fluorophore DHX, resulting in a fluorescence turn-on response. Under the optimized conditions (EtOH/H 2 O, 1:1, v /v, pH 7.0), DHX-DT exhibited superior sensitivity with a detection limit of 7.0 nM, whereas DHX-PTC displayed a remarkably faster response, reaching equilibrium within 3 min, with a detection limit of 12.6 nM. Both probes showed excellent selectivity toward Hg 2+ over various competing metal ions and strong anti-interference capability. The sensing mechanisms were unequivocally verified by 1 HNMR, HRMS and DFT calculations. Furthermore, practical applicability was demonstrated through the determination of Hg 2+ in real environmental water samples, affording satisfactory recoveries of 95.50–104.50% and good agreement with ICP-OES measurements. The present work provides a direct comparative evaluation of two representative Hg 2+ -responsive recognition motifs within a unified DHX-based sensing platform, offering practical guidance for the rational screening of recognition units in the construction of reaction-based fluorescent probes for Hg 2+ detection. Download: Download high-res image (114KB) Download: Download full-size image