Calculations on the origin of hyperporphyrin spectra in sequentially protonated meso-(dimethylaminophenyl) porphyrins

Abstract

ABSTRACT:The spectra of porphyrins meso-substituted by 4-dimethylaminophenyl groups and protonated at the central pyrrole nitrogens show strong new bands in the visible (450-600 nm) and far-red (700-780 nm). On complete protonation the observed spectra are essentially normal except for enhanced intensity in the farthest red band at $650 nm. The new bands observed with partial protonation have been qualitatively interpreted as hyperporphyrin spectra due to transitions from 'the filled p orbitals on the amino nitrogen atoms … to the porphyrin LUMOs' [Ojadi ECA, Linschitz M, Gouterman M, Walter RI, Lindsey JS, Wagner RW,]. We now report spectra calculated using the CAChe computer program package. The best structures are determined by energy minimization using a semi-empiral AM1 algorithm; a semi-empirical INDO/CI calculation is then used to obtained the excited state transition energies and intensities. The calculated spectra, although generally blue-shifted compared to experiment, reproduce the hyperporphyrin spectra in those cases where they are observed. In these cases, in contrast to species with normal porphyrin spectra, the HOMO or HOMO-1 is not an orbital on the porphyrin ring but is rather a p-orbital on the unprotonated amino nitrogen that extends over the associated phenyl ring. The calculations suggest that the hyperporphyrin transitions are of Ph(p) → Por(p*) origin, where Ph(p) is an orbital on the phenylamine substitutent and Por(p*) is a LUMO on the porphyrin. It is further suggested that in the fully protonated species the intensity enhancement of the farthest red band in an otherwise normal porphyrin spectrum may relate to phenyl character in the HOMO or HOMO-1.

Polymethacrylic zinc porphyrin: A new approach to chiral recognition

“…At the same time, the Q bands at 515 and 550 nm progressively decrease of intensity, while those at 590 and 645 nm increase. As suggested by Gouterman and subsequently proved by means of semiempirical calculations [34,37,38], the observed red-shift of the Soret band of 21 nm reflects the occurrence of phenyl-to-porphyrin charge transfer transitions.…”

Application of the electronic spectra of porphyrins for analytical purposes: The effects of metal ions and structural distortions

“…its field, p-or d-, in the periodic table) he made subcategories: among our results in Table 1 In this categorization of metalloporphyrins, Gouterman did not take the steric (distorting) effects into consideration, only the electronic effects of metal ion (through its electron configuration). Therefore he had to slightly modify his aspect on the basis of his own experiences with metal-free, more exactly protonated porphyrins, which showed hyperporphyrin character too [91]. The real origin of these large redshifts is the highly distorted structure.…”

Aggregation Properties of Hyperporphyrins with Hydroxyphenyl Substituents

“…In these cases, or in the presence of peripheral amino or hydroxyl substituent groups, lone pair orbitals with the correct symmetry are available for a charge-transfer transition from the donor atom to the porphyrin. [10][11][12][13][14][15][16] To the best of our knowledge, the formation of aggregates, which would also lead to broadened and red-shifted extinction features, has not been reported in the literature for porphyrins functionalized with hydroxyphenyl or aminophenyl groups. Following our interest in the behavior of porphyrins upon acidification in organic solvents, we have already investigated tetraphenylporphyrin (TPP), 29 the three isomers of tetrakis-(pyridyl)porphyrin (TpyP), 30 and the tetrabutylammonium salt of tetrakis(4-sulfonatophenyl)porphyrin (TPPS).…”