An ultrasensitive colorimetric and fluorescent "turn-on" chemosensor based on Schiff base for the detection of Cu in the aqueous medium.

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 H NMR, FT-IR, and fluorescence spectroscopy, and its sensing properties were studied toward Mn, Cu, Pb, Cd, Na, Ni, Al, K, Ag, Zn, Co, Cr, Hg, Ca, and Mg. SB showed an excellent colorimetric (yellow to yellowish brown) in MeOH and fluorescence "turn-on" sensing response to Cu in MeOH/Water (10/90, v/v) media. The sensing mechanism of SB toward Cu was investigated by FT-IR, H NMR titration, DFT studies, and Job's plot analysis. The detection limit was calculated to be very low 0.0025 µg mL (0.0025 ppm). Furthermore, the test strip containing SB also showed excellent selectivity and sensitivity toward Cu in a solution medium and when supported on a solid medium.