A Novel Imidazole Bound Schiff Base as Highly Selective "Turn-on" Fluorescence Sensor for Zn2+ and Colorimetric Kit for Co2+

An imidazole based Schiff base (2-[(1H-imidazole-2-ylmethylene)-amino]-4-methyl-phenol) (IMP), with an imine unit, has been designed and characterized by various standard methods. The evaluation of the probe as a fluorogenic sensor for Zn2+ and a chromogenic sensor for Co2+ has been rationalized in terms of the PET mechanism. In the presence of Zn2+, a light yellow colored solution of IMP with maximum absorption of 364 nm becomes bright yellow with maximum absorption of 410 nm and a measurable fluorescent signal at 612 nm with bathochromic enhancement. The sensitivity of the fluorescent based assay (6.78 x 10(-9) M) for Zn2+ is far below the limit in the World Health Organization (WHO) guidelines for drinking water (7.6 x 10(-5) M) and therefore it is capable of being a practical system for the monitoring of Zn2+ concentrations in aqueous samples. Moreover, IMP showed a highly selective colorimetric response to Co2+ by displayed an obvious pink color upon addition of metal solution immediately without any interference from other ions. These results provide a new approach for selectively recognizing the two most important trace elements in the human body simultaneously, for Zn2+ by emission spectra and Co2+ by the naked eye. Grpahical Abstract