jp5b05129_si_001.pdf (2.56 MB)
Application of Time-Dependent Density Functional and Natural Bond Orbital Theories to the UV–vis Absorption Spectra of Some Phenolic Compounds
journal contribution
posted on 2015-09-03, 00:00 authored by Svetlana Marković, Jelena TošovićThe UV–vis
properties of 22 natural phenolic compounds,
comprising anthraquinones, neoflavonoids, and flavonoids were systematically
examined. The time-dependent density functional theory (TDDFT) approach
in combination with the B3LYP, B3LYP-D2, B3P86, and M06-2X functionals
was used to simulate the UV–vis spectra of the investigated
compounds. It was shown that all methods exhibit very good (B3LYP
slightly better) performance in reproducing the examined UV–vis
spectra. However, the shapes of the Kohn–Sham molecular orbitals
(MOs) involved in electronic transitions were misleading in constructing
the MO correlation diagrams. To provide better understanding of redistribution
of electron density upon excitation, the natural bond orbital (NBO)
analysis was applied. Bearing in mind the spatial and energetic separations,
as well as the character of the π bonding, lone pair, and π*
antibonding natural localized molecular orbitals (NLMOs), the “NLMO
clusters” were constructed. NLMO cluster should be understood
as a part of a molecule characterized with distinguished electron
density. It was shown that all absorption bands including all electronic
transitions need to be inspected to fully understand the UV–vis
spectrum of a certain compound, and, thus, to learn more about its
UV–vis light absorption. Our investigation showed that the
TDDFT and NBO theories are complementary, as the results from the
two approaches can be combined to interpret the UV–vis spectra.
Agreement between the predictions of the TDDFT approach and those
based on the NLMO clusters is excellent in the case of major electronic
transitions and long wavelengths. It should be emphasized that the
approach for investigation of UV–vis light absorption based
on the NLMO clusters is applied for the first time.