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Issue 5, 2015
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The origin of the absorption spectra of porphyrin N- and dithiaporphyrin S-oxides in their neutral and protonated states

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Abstract

meso-Tetraphenylporphyrin N-oxide (1) and meso-tetraphenyl-21,23-dithiaporphyrin S-oxide (3) possess optical spectra that are distinctly different from their parent porphyrins, meso-tetraphenylporphyrin (2) and meso-tetraphenyl-21,23-dithiaporphyrin (4), respectively. The hyperporphyrin spectra were reproduced and classified using TD CAM-B3LYP and SCS-CC2 computational methods. Calculations revealed the electronic and conformational influences of the N- and S-oxide functionalities. While the N-oxide under acidic conditions forms a dication with a UV-vis spectrum that is nearly indistinguishable from that of the diprotonated parent porphyrin, the diprotonated S-oxide possesses a much different UV-vis spectrum from diprotonated parent dithiaporphyrin. A computational study of the protonation events revealed the site and degree of protonation and rationalized the regular and hyperporphyrin UV-vis spectra of the neutral and protonated species, respectively. The study illuminates the electronic effects of the relatively rare modification of the inner porphyrin heteroatoms. It also illustrates a case in which TD CAM-B3LYP reaches its limits to make reliable predictions about the optical properties of a porphyrinoid, making the use of higher methods essential.

Graphical abstract: The origin of the absorption spectra of porphyrin N- and dithiaporphyrin S-oxides in their neutral and protonated states

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Article information


Submitted
15 Oct 2014
Accepted
11 Dec 2014
First published
11 Dec 2014

Phys. Chem. Chem. Phys., 2015,17, 3560-3569
Article type
Paper

The origin of the absorption spectra of porphyrin N- and dithiaporphyrin S-oxides in their neutral and protonated states

T. Bruhn and C. Brückner, Phys. Chem. Chem. Phys., 2015, 17, 3560
DOI: 10.1039/C4CP04675G

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