Manifestation of Structural Features of Porphyrin Molecules in Their Electronic Absorption Spectra

摘要

The hypothesis on the nature of the intense Soret absorption band in the 350–450-nm region in the electronic spectra of tetra-fragmentary aromatic compounds previously suggested in the literature is discussed. An attempt is made to explain some experimental data on the basis of this hypothesis. It is shown that the Soret band in porphyrins (H2P) can result from the phototransfer of the electron density from pyrrole rings to the macrocyclic chromophore system. The electronic absorption spectra of porphyrins and their azo-derivatives are used to analyze data that can be obtained from the magnitude I of the shift of the long-wavelength absorption band I caused by protonation of these compounds. It is shown that I can be used in different cases to characterize the stability of the protonated form of the H2P molecule and the expansion of its chromophore system upon protonation or the site of attachment of a proton in a molecule.