1,8-Naphthalimide derived dual-functioning fluorescent probe for “turn-off” and ratiometric detection of Cu2+ based on two distinct mechanisms in different concentration ranges

Abstract

In this study, a novel 1,8-naphthalimide derived compound bearing the coumarin moiety called 7-Diethylaminocoumarin-3-aceone (N-hydroxyethyl-1’,8’-naphthalimide-4’-) hydrazone (1) has been designed, synthesized and evaluated as a dual-functioning fluorescent probe for “turn-off” and ratiometric detection of Cu2+ based on two distinct mechanisms in different concentration ranges in aqueous solution. This probe 1 showed high selectivity and sensitivity for Cu2+ over other common metal ions, for the limit of detection (LOD) could reach 3.90 × 10−8 M and 3.26 × 10−7 M for “turn-off” and ratiometric detection respectively. Moreover, in Cu2+ equivalence range of 0–0.5, a decrease in fluorescence emission intensity at 441 nm was observed upon addition of Cu2+, but in Cu2+ equivalence range of over 0.5, a new emission band centered at 462 nm appeared with increasing intensity accompanied by a decrease in fluorescence emission intensity at 570 nm, which provided ratiometric fluorescence detection of Cu2+. The sensing mechanisms for the responses of 1 to Cu2+ were chelation-quenched fluorescence (CHQF) and chemical reaction between 1 and Cu2+ over Cu2+ equivalence range of 0–0.5 and more than 0.5, respectively. Thus, this probe 1 could be utilized for sensing and monitoring Cu2+ in environmental and biological systems in different concentration ranges.