Benzothiazolylhydrazone-Based Turn-on Fluorescent Probe for Detecting Cu2+: S-donor as a Cu2+-induced Fluorescence Quenching Inhibitor

Abstract

The fluorescent turn-on detection of metal ions is highly desirable for public health and environmental security. Herein, we report a rationally designed fluorescent probe (1) for the detection of Cu²⁺ synthesized by integrating 2-hydrazinylbenzothiazole with 3-acetyl-7-hydroxycoumarin. The probe alone is non-fluorescent due to the isomerization of C=N in the excited state. The addition of Cu²⁺ can cause a delayed fluorescence enhancement. A comparative study of 1 and its analogues indicated that the turn-on fluorescence response was thanks to the sulfur atom coordinating to Cu²⁺. The response delay of 1 in sensing Cu²⁺ was ascribed to the gradual transition from N-coordination to S-coordination (N and S in thiazole moiety). The proposed new function of S-donor would provide a new approach for the turn-on fluorescence sensation of Cu²⁺.