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.