A highly selective and naked-eye sensor for Hg²⁺ based on quinazoline-4(3H)-thione

A highly selective colorimetric and fluorescent sensor for Hg²⁺, TPS (TPS = 2-(4-(diphenyl-amino)phenyl)quinazoline-4(3H)-thione), based on a 2-substituted quinazoline-4(3H)-thione derivative, was designed and characterized in this paper. TPS displays relatively strong fluorescence centered at about 468 nm. When mixing with Hg²⁺, TPS interacts with Hg²⁺ in a 2:1(TPS-Hg²⁺) stoichiometry via a coordination bond interaction between the sulfur atom and Hg²⁺ with an association constant of 4.17 × 10⁸ M^-2 (R² = 0.96). Upon addition of Hg²⁺, TPS showed a remarkable decrease in fluorescence spectra (468 nm) with a clear color change from yellow to red, so TPS could serve as a naked-eye sensor for Hg²⁺. The sensor allow determination of Hg²⁺ in the working range 2.0 μM-12.0 μM with a detection limit of 1.5 μM. Upon addition of KI to the solution of TPS-Hg²⁺ species, the spectra can be restored to the original spectrum in both absorption and fluorescence and indicates that this sensor could be reused. The sensor exhibited excellent reproducibility, reversibility and selectivity.