An ultrasensitive colorimetric and fluorescent "turn-on" chemosensor based on Schiff base for the detection of Cu²⁺...

We designed and synthesized a fluorescent "turn-on" and colorimetric chemosensor ((E)-1-((p-tolylimino)methyl)naphthalen-2-ol) SB. The structure of the synthesized chemosensor was investigated by ¹H NMR, FT-IR, and fluorescence spectroscopy, and its sensing properties were studied toward Mn²⁺, Cu²⁺, Pb²⁺, Cd²⁺, Na⁺, Ni²⁺, Al³⁺, K⁺, Ag⁺, Zn²⁺, Co²⁺, Cr³⁺, Hg²⁺, Ca²⁺, and Mg²⁺. SB showed an excellent colorimetric (yellow to yellowish brown) in MeOH and fluorescence "turn-on" sensing response to Cu²⁺ in MeOH/Water (10/90, v/v) media. The sensing mechanism of SB toward Cu²⁺ was investigated by FT-IR, ¹H NMR titration, DFT studies, and Job's plot analysis. The detection limit was calculated to be very low 0.0025 µg mL^-1 (0.0025 ppm). Furthermore, the test strip containing SB also showed excellent selectivity and sensitivity toward Cu²⁺ in a solution medium and when supported on a solid medium.