Rhodamine-based Hg²⁺-selective chemodosimeter in aqueous solution: fluorescent OFF-ON

(Chemical Equation Presented) N-(Rhodamine-6G)lactam-N′- phenylthiourea-ethylenediamine (1) was developed as a fluorescent and colorimetric chemodosimeter in aqueous solution with a broad pH span (5-10) and high selectivity toward Hg²⁺ but no significant response toward other competitive cations, such as Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Cd²⁺, Ca ²⁺, Mg²⁺, K⁺, Na⁺, etc. The Hg ²⁺-promoted ring opening of spirolactam of the rhodamine moiety induced cyclic guanylation of the thiourea moiety, which resulted in the dual chromo- and fluorogenic observation (OFF-ON).