Abstract
The one- and two-photon absorption characteristics of the Porphyrin isomers Porphycene, Corrphycene, Hemiporphycene, N-confused Porphyrin, cis- and trans-Doubly confused Porphyrins, the newly synthesised Neo-confused Porphyrin, and a set of core-substituted Porphycenes are systematically investigated using linear and quadratic density functional response theory. It is shown that, despite the one-photon spectra displaying characteristic Soret- and Q-regions, the classic Gouterman four orbital theory has limitations for the analysis of the absorptions in this series of compounds. Generated spectra for the two-photon absorptions are shown to be very sensitive to the isoelectronic changes, contrary to the one-photon spectra. This accesses a potentially powerful tool by which the two-photon absorption can be fine-tuned without large structural changes to the nature of the macrocycle.
Highlights
The photochemistry of porphyrin (P in Fig. 1) systems is a vast area that involves chemistry and biology as well as materials and medicinal science
The optimization results of the reduced porphyrin isomers, with their pyrrolic hydrogen atoms in the cis as well as transposition, all resulted in a planar series of systems, apart from cis-Pc-2 (Fig. 2 and Fig. 3)
The Gouterman Four Orbital (GFO) model was developed for the P macrocycle and was derived based on the degeneracy of the two LUMO orbitals
Summary
The photochemistry of porphyrin (P in Fig. 1) systems is a vast area that involves chemistry and biology as well as materials and medicinal science. Non-linear absorption properties, such as two-photon absorption (TPA), is a fairly recent focus of the photochemistry of P. For applications of non-linear materials, such as 3D optical storage, this is clearly a key property, but it is of great interest in applications in a biological environment. This is due the fact that conventional linear absorption of P-type compounds rarely have their wavelengths of maximum absorption located inside the optical window of tissue penetration, a limiting factor for biological applications. TPA can be a useful tool for deeper access into biological samples
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