Switching the recognition preference of thiourea derivative by replacing Cu2+: spectroscopic characteristics of aggregation-induced emission and mechanism studies for recognition of Hg(II) in aqueous solution

A thiourea-functionalized π-conjugated cyanostilbene derivative of (Z)-N-((4-(2-cyano-2-phenylvinyl)phenyl)carbamothioyl)acetamide (CN-S) has been designed, synthesized and characterized by standard spectroscopic analyses. CN-S exhibited excellent aggregation-induced emission property in DMSO/water mixture with high water fraction and showed highly selective and sensitive recognition towards Cu2+ and Hg2+ ions with large fluorescence changes. On addition of Cu2+ to CN-S, it displayed a turn-off fluorescent response and generated a Cu–CN-S complex which was also confirmed by theoretical calculation. However, the complex of Cu–CN-S showed a turn-on fluorescent response to Hg2+ with high selectivity and sensitivity because of a desulfurization reaction. In addition, there is a good linear relationship (R2 = 0.9966) between the fluorescence intensity and the concentration of Hg2+. The detection limit of Hg2+ is 45 nM. By this novel strategy, this single molecule (CN-S) can be used as fluorescent sensor to detect Hg2+ specifically.