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Photoionization of tetrapyrrole macrocycles: Porphyrin isomers and corrole tautomers

•Electronic structures of porphyrins and corroles.•Simulated UV photoelectron spectra of porphyrins and corroles in the gas phase.•Relationship between the electronic structures, spectra and aromaticity. The electronic structures of tetrapyrrole macrocycles: porphyrin’s structural isomers and corrol...

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Published in:Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2022-05, Vol.427, p.113849, Article 113849
Main Author: Novak, Igor
Format: Article
Language:English
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Summary:•Electronic structures of porphyrins and corroles.•Simulated UV photoelectron spectra of porphyrins and corroles in the gas phase.•Relationship between the electronic structures, spectra and aromaticity. The electronic structures of tetrapyrrole macrocycles: porphyrin’s structural isomers and corrole tautomers have been investigated using high-level ab initio method: Green’s function method (OVGF). The vertical, valence ionization energies were calculated and gas phase photoelectron spectra simulated on the basis of these ionization energies. The Franck-Condon analysis of vibronic effects has also been performed and changes between molecular geometries in neutral and ionic ground state have been discussed. Relative energies (standard formation enthalpies) for isomers have been calculated using composite G4MP2 method. The results help in understanding of how is the electronic structure affected when molecule deviates from planar geometry and what is the influence of changes in ring-ring linkages. We have demonstrated that the electronic structures (reflected in ionization energies) of title compounds (as free, unsubstituted bases) are not significantly perturbed when molecular geometry deviates from planarity. We also discuss the relationship between lowest band ionization energy and aromaticity of porphyrins and corroles.
ISSN:1010-6030
1873-2666
DOI:10.1016/j.jphotochem.2022.113849