Tuning of the optical properties of chiral Schiff base Zn(II) complexes by substituents

Abstract

Three new chiral Schiff base zinc(II) complexes, bis(N-R-1-phenylethyl-3-methoxysalicydenaminato) zinc(II), bis(N-R-1-naphthylethyl-3-methoxysalicydenaminato) zinc(II) and bis(N-R-1-naphthylethyl-5-methoxysalicydenaminato) zinc(II), have been prepared and characterized structurally. They are found to have a distorted square planar or compressed tetrahedral trans-[ZnN2O2] coordination geometry. Their UV–Vis and CD spectra exhibit intense intraligand transition bands, which are affected by the positions of the substituted methoxy groups of the aldehyde moieties rather than the extension of the π-conjugated ring (phenyl or naphthyl) groups of the amine moieties. A similar dependence of the molecular structures can also be found in the case of the fluorescence spectra, which is in agreement with a comparison with analogous zinc(II) complexes. The results of computational chemistry, which was performed to simulate UV–Vis and CD spectra for these complexes, suggest that the correlation between the effects of substitution and HOMO–LUMO gaps associated with the most intense intraligand transitions can be reasonably explained.