Organic radical-induced Cu²⁺ selective sensing based on thiazolothiazole derivatives

As a new approach to detect Cu²⁺, colorimetric detection of Cu²⁺ via organo radical formation of thiazolothiazole is reported. Upon the addition of Cu²⁺, thiazolothiazole derivatives 1 and 2 form relatively stable organo radicals, resulting in a distinct colorimetric change from greenish yellow to blue. Among the various metal ions, only Cu²⁺ showed a new peak appearance at 610 nm. In addition, a selective fluorescence quenching was also observed with Cu²⁺. To understand the origin of the Cu²⁺ selectivity of 1 and 2, series of electrochemical data are reported. Finally, EPR (electron paramagnetic resonance) data clearly support the formation of this unique organic radical formation.