Oxidative cyclization of thiosemicarbazone: an optical and turn-on fluorescent chemodosimeter for Cu(ii)

Abstract

A weakly fluorescent thiosemicabazone (L₁H) was found to be a selective optical and “turn-on” fluorescent chemodosimeter for Cu²⁺ ion in aqueous medium. A significant fluorescence enhancement along with change in color was only observed for Cu²⁺ ion; among the other tested metal ions (viz.Na⁺, K⁺, Mg²⁺, Ca²⁺, Cr³⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺, Ag⁺, Ni²⁺, Co²⁺, Fe³⁺ and Mn²⁺). The Cu²⁺ selectivity resulted from an oxidative cyclization of the weak fluorescent L₁H into highly fluorescent rigid 4,5-dihydro-5,5-dimethyl-4-(naphthalen-5-yl)-1,2,4-triazole-3-thione (L₂). The signaling mechanism has been confirmed by independent synthesis with detail characterization of L₂.