The Hyperporphyrin Concept: A Contemporary Perspective

Authors

Carl C. Wamser, Portland State UniversityFollow
Abhik Ghosh, The Arctic University of Norway

Published In

JACS Au

Document Type

Article

Publication Date

6-2022

Subjects

Gouterman four-orbital model, Aromatic compounds, Pyrroles, Reaction mechanisms, Resonance structures, Substituents

Abstract

The Gouterman four-orbital model conceptualizes porphyrin UV–visible spectra as dominated by four frontier molecular orbitals─two nearly degenerate HOMOs and two exactly degenerate LUMOS under D4h symmetry. These are well separated from all the other molecular orbitals, and normal spectra involve transitions among these MOs. Unusual spectra occur when additional orbitals appear in this energy range, typically as a consequence of the central coordinated atom. For example, metals with empty d orbitals in a suitable energy range may lead to charge transfer from porphyrin (ligand) to metal, that is, so-called LMCT transitions. Metals with filled p or d orbitals may lead to charge transfer from metal to porphyrin, MLCT transitions. These cases lead to additional peaks and/or significant redshifts in the spectra and were classified as hyperporphyrins by Gouterman. Cases in which spectra are blueshifted were classified as hypsoporphyrins; they are common for relatively electronegative late transition metal porphyrins. Many of the same principles apply to porphyrin analogues, especially corroles. In this Perspective, we focus on two newer classes of hyperporphyrins: one reflecting substituent effects in protonated or deprotonated free-base tetraphenyporphyrins and the other reflecting “noninnocent” interactions between central metal ions and corroles. Hyperporphyrin effects on spectra can be dramatic, yet they can be generated by relatively simple changes and subtle structural variations, such as acid–base reactions or the selection of a central metal ion. These concepts suggest strategies for engineering porphyrin or porphyrinoid dyes for specific applications, especially those requiring far-red or near-infrared absorption or emission.

Rights

Copyright © 2022 The Authors. Published by American Chemical Society

This work is licensed under a Creative Commons Attribution 4.0 International License.

Locate the Document

https://doi.org/10.1021/jacsau.2c00255

DOI

10.1021/jacsau.2c00255

Persistent Identifier

https://archives.pdx.edu/ds/psu/38239

Citation Details

Wamser, C. C., & Ghosh, A. (2022). The Hyperporphyrin Concept: A Contemporary Perspective. JACS Au.