Substituent effects on electronic structure and spectral property of Zn(II) complexes based on the OONX ligands: DFT and TDDFT theoretical studies

Abstract

The ground-state geometric structures of three chiral ligands OON1(2-(hydroxyl(pyridine-2-yl)-methyl)methoxyphenol), OON2(2-(1-hydroxy-1-(pyridine-2-yl)ethyl)phenol), and OON3(2-(hydroxyl(phenyl)pyridine-2-yl)methyl)phenol) and three Zn(II) complexes ([trans-R-Zn(OON1)Cl2] (A), [trans-R-Zn(OON2)Cl2] (B), and [trans-R-Zn(OON3)Cl2] (C)) are theoretically investigated by Becke's three-parameter nonlocal-exchange functional with the nonlocal correlation of Lee–Yang–Parr method (B3LYP). Then, the spectra properties are evaluated by time-dependent B3LYP (TD-B3LYP) method with polarized continuum model (PCM) in different media based on the optimized ground-state geometries. The detailed transition characters are assigned for main absorptions, and an absorption peak with high intensity around 190nm that is not detected in experiment is obtained. Moreover, the effect of different substituents on electronic spectra is explored. The results indicate that the electron-donating substituent group destabilize the energy level of HOMO (the highest occupied molecular orbital) and stabilize the energy level of LUMO (the lowest unoccupied molecular orbital), which leads to the decreased H(HOMO)–L(LUMO) energy gap. Consequently, the lowest-lying transition energy increased in an order of A<B<C, which is consistent with the variation rule of the H–L energy gap.