Abstarct: In this study, the quantum calculations of the dimer of 4-Nitro-2 - (((2-mercaptoethyl) imino) methyl) –phenol (N-H2L) and its complexation with Zn, Zn(N-HL)+, performed for the structural optimization, the first singlet excitation, the vertical transition energy and fluorescence in the ground and first excited state for both gas and the aqueous phase. The results of this calculations compared with those of H2L and Zn(HL)+. Calculations were performed using Turbomol program at the B3LYP level of theory and the cc-pVDZ and def2-TZVP basis sets.The studied structures were drawn using the energy of the singlet excitation UV spectra.NO2 substitutions decreased the bond length and increased the frequency of the total ring bonds. Geometric parameters such as bond lengths and bond angles in the studied structures were compared.The results showed NO2 substitution in the phenolic ring leads to a decrease in the bond length and thus increases the frequency of the chelating ring bonds This is the same as the results of vibration modes. Fluorescence emission calculations showed that the emission of the studied compounds appears in the visible area But the emission fluorescence of Zn(N-HL) complex appears above the visible wavelength. This can indicate that the use of complex in the diagnosis process is effective in treatment.