Dual-Mode Semisquaraine-Based Sensor for Selective Detection of Hg²⁺ in a Micellar Medium

A novel chemosensor based on semisquaraine dye (SSQ) for selective detection of Hg²⁺ is described. SSQ is obtained in quantitative yields from the reaction between squaric acid and 6-ethoxy-2-quinaldinium iodide. SSQ in combination with surfactant shows a dual chromogenic and fluorogenic response selectively toward Hg²⁺ as compared to Li⁺, Na⁺, K⁺, Ag⁺, Ca²⁺, Mg²⁺, Zn²⁺, Pb²⁺, Cd²⁺, Cu²⁺, and Fe³⁺ due to the soft acid nature and size of the mercuric ion.