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

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 Hg ²⁺, the spirothiolactone showed a 1:1 stoichiometry for the Hg ²⁺ 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.