Quantum-Chemical Study of the Structure, Vibrational Spectra, and Isotopic Effects of Chlorin: Force Field Modeling, Scaling, and Correlation with Porphine
E. Yu. Stepanovich1, A. M. Likhter1, K. V. Berezin2, V.V. Nechaev3
1 V.N. Tatishchev Astrakhan State University, Astrakhan, Russia
2 N.G. Chernyshevsky Saratov State National Research University, Saratov, Russia
3 Saratov State Technical University named after Yuri Gagarin, Saratov, Russia.
Abstract
The structure, normal vibration frequencies, and absolute IR band intensities of the chlorin molecule and its four symmetric isotopomers have been calculated
using the DFT/B3LYP method with the 6-31G(d) basis set. Scaling of the force field was performed using the Pulay method in both independent and dependent natural coordinates.
A procedure for obtaining effective force fields without using experimental data on fundamental vibration frequencies is proposed.
By comparing the vibrational modes and constructing special transformation matrices, a complete correlation of the fundamental vibrations of
porphine and chlorin has been established. It is shown that most vibrations of the porphine macrocycle retain their frequency characteristic upon hydrogenation
of the pyrrolenine ring, with only 12 vibrations undergoing significant changes. A frequency correlation is established taking into account the mode conversion
between chlorin and all considered isotopomers. A comparative analysis of the force fields of porphine and chlorin in dependent natural coordinates revealed
the nonlocal nature of the changes in the macrocycle force constants upon hydrogenation of one pyrrolenine ring.
Simulation of the IR spectra of chlorin and its isotopomers has been performed. The frequencies have been assigned and the normal vibrations of the investigated
molecules have been interpreted.
Speaker
Ekaterina Yu. Stepanovich
V.N. Tatishchev Astrakhan State University, Astrakhan, Russia
Russia
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