Rhodamine–pyrene conjugated chemosensors for ratiometric detection of Hg2+ ions: Different sensing behavior between a spirolactone and a spirothiolactone

• We synthesized two rhodamine–pyrene conjugated ratiometric chemosensors.
• The two sensors were differentiated by a spirothiolactone and a spirolactone unit.
• With Hg2+, the spirothiolactone sensor exhibited a weakened FRET behavior.
• The spirolactone sensor was hydrolyzed inducing a monomer–excimer switch with Hg2+.
• Both sensors exhibited colorimetric and fluorescent dual-responses toward Hg2+.

Two novel rhodamine–pyrene conjugated chemosensors were successfully designed and synthesized, which exhibited high affinity to Hg2+ ions. As ratiometric chemosensors, each displayed highly selective and sensitive colorimetric and fluorogenic dual-responses toward Hg2+. The comparison of two chemosensors indicated that the spirothiolactone containing sensor was superior to the spirolactone analog in sensing behavior when detecting Hg2+, presumably due to the thiophilic nature of mercury and the different sensing mechanisms in operation. Upon interaction with Hg2+, the spirothiolactone showed a 1:1 stoichiometry for the Hg2+ complex, accompanied with a weakened fluorescence resonance energy transfer (FRET) behavior. However, the spirolactone was hydrolyzed and consequently induced the monomer–excimer switch of the resulted pyrene in the presence of Hg2+ ions.

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