DFT and HF Studies of the Geometry,Electronic Structure,and Vibrational Spectra of 2-Nitrotetraphenylporphyrin and Zinc 2-Nitrotetraphenylporphyrin

摘要

The ground-state geometries and electronic structures of 2-nitrotetraphenylporphyrin (H_2-2-NO_2-TPP) and zinc 2-nitrotetraphenylporphyrin (Zn-2-NO_2-TPP) with C_s and C_1 symmetry have been determined from density functional theory,using the Becke-Lee-Yang-Parr composite exchange-correlation functional (B3-LYP) and ab initio RHF method and 6-31G(d) basis set.The optimized geometries are then compared with the crystallographic data of related compounds.The energy and electronic structures of different conformers are analyzed and compared with each other.The conformers with C_1 symmetry are found to be more stable than that of C_s symmetry.The relative order of the highest occupied a_(2u) and a_(1u) orbitals determined by B3LYP (a_(2u)>a_(1u)) is reversed by RHF (a_(1u)>a_(2u)).The vibrational wavenumber,IR,and Raman intensities are also calculated at B3LYP/6-31G(d) optimized geometries.The calculated wavenumbers are scaled by a uniform scaling factor and compared with the experimental one.Most of the scaled modes are found to be in good agreement with the observed fundamentals.A single beta-NO_2 substitution slightly changes the geometries,the vibrational wavenumbers,and the frontier orbitals energy level.