Visual colorimetric and fluorescence turn-on probe for Cu(II) ion based on coordination and catalyzed oxidative cyclization of ortho amino azobenzene

Abstract

2,2′-diaminoazobenzene (L1), a visual colorimetric and fluorescence turn-on detection probe for Cu2+ ion, has been discovered successfully. The yellow L1 solution changed into light-purple solution rapidly with dropping of Cu2+ ion observed by the naked eyes, for the formation of 1:1 complex of L1 and Cu2+ ion calculated by Job-plot method. Non-emissive L1 transformed into 2-(2-aminophenyl) benzotriazole (L1-BTA) with strong fluorescence at the peak around 475 nm, owing to the Cu2+ catalyzed oxidative cyclization of L1, accompanied by the fluorescence intensity gradually increasing within 20 min. And L1 was applied for quantitative detection of Cu2+ with good linear relationship between its UV absorbance and Cu2+ concentration, and exhibited high fluorescence selectivity toward Cu2+ over other metal ions (Fe3+, Zn2+, Cd2+, Co2+, Ni2+, Mn2+, Na+, Al3+ and Ca2+) in EtOH solution.