1. Calculations of derivatives of porphin and porphyrazine with an annulated five-membered heteroaromatic ring using a modified INDO method.
- Author
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Volkovich, D., Kuzmitsky, V., and Stuzhin, P.
- Subjects
PYRROLES ,HETEROCYCLIC compounds ,SPECTRUM analysis ,ABSORPTION spectra ,CONDENSATION ,QUANTUM chemistry ,MOLECULAR spectroscopy ,PHYSICAL & theoretical chemistry - Abstract
Quantum-chemical calculations for series of porphin (H
2 P) and porphyrazine (H2 PA) derivatives whose molecules contain a 3,4-annulated five-membered heteroaromatic ring of pyrrole, furan, and thiophene as well as 1,2,5-triazole, 1,2,5-oxadiazole, and 1,2,5-thiadiazole have been carried out by the AM1 and INDO/Sm methods (m means “modified parametrization”). As follows from the unrestricted Hartree-Fock AM1 calculations, the ground state energy of the a isomer is lower than that of the b isomers for all compounds, the a and b isomers being NH isomers with the additional five-membered ring fused to a pyrrolenine or pyrrole ring, respectively. Condensation of the five-membered ring for the b isomers of the H2 P derivatives is shown to extend the main conjugation path from 18-membered to 21-membered cyclopolyene. However, the 18-membered cyclopolyene for the a isomers of the H2 P derivatives and 16-membered cyclopolyene for both isomers of the H2 PA derivatives prove to be isolated from the five-membered ring carrying six π-electrons. Based on INDO/Sm computations of electronic absorption spectra of the H2 P and H2 PA derivatives, it is shown that the Qx level of the a isomers is sensitive to the nature of the annulated ring whereas the Qy level is practically not shifted. On the contrary, the Qx level of the b isomers is relatively insensitive to the nature of the annulated ring while the Qy level decreases monotonously in the H2 P and H2 PA series, being the first excited state level for the majority of the derivatives (X is along the NH-HN axis; Y, perpendicular to it). The electronic absorption spectra at the border of the visible and near-UV regions are determined mainly by two high-intensity G → Bx and G → By transitions for the H2 P derivatives. However, four intense G → Bx , G → By , G → Nx , and G → Ny transitions are characteristic of the spectra of the H2 PA derivatives. [ABSTRACT FROM AUTHOR]- Published
- 2008
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