Porphyrins as Photoredox Catalysts: Experimental and Theoretical Studies

Abstract

Metalloporphyrins not only are vital in biological systems but also are valuable catalysts in organic synthesis. On the other hand, catalytic properties of free base porphyrins have been less explored. They are mostly known as efficient photosensitizers for the generation of singlet oxygen via photoinduced energy transfer processes, but under light irradiation, they can also participate in electron transfer processes. Indeed, we have found that free base tetraphenylporphyrin (HTPP) is an efficient photoredox catalyst for the reaction of aldehydes with diazo compounds leading to α-alkylated derivatives. The performance of a porphyrin catalyst can be optimized by tailoring various substituents at the periphery of the macrocycle at both the β and meso positions. This allows for the fine tuning of their optical and electrochemical properties and hence their catalytic activity.

Peripherally Metalated Porphyrins with Applications in Catalysis, Molecular Electronics and Biomedicine

“…Some challenging reactions could surprisingly be achieved or enhanced with such systems under visible light irradiation (“photo‐assisted” catalysis). Porphyrin derivatives, which have redox potentials in their excited states and their ground states close to those of [Ru(bpy) 3 ] 2+ , can be used for photocatalytic applications such as reduction of CO 2 to CO or H 2 evolution.…”

Merging Triptycene, BODIPY and Porphyrin Chemistry: Synthesis and Properties of Mono‐ and Trisubstituted Triptycene Dye Arrays

“…The HOMO–LUMO gaps of these porphyrins were in the range of 2.18–2.21 V, smaller than that of TPP (2.23 V). The redox properties of these meso ‐triptycenylporphyrins are similar to regular porphyrins indicating that these systems might be suitable as photoredox catalysts.…”

Investigating Electronic Communications in meso–meso Ethene‐Bridged Unsymmetrical Diporphyrins

“…Introduction of coordinating metals into the porphyrin framework is yet another valuable strategy to tailor the resulting electronic properties . Understanding the impact that the coordinating metals exert on the porphyrin framework is of paramount importance due to the increasing interest in porphyrin‐driven catalysis . To this end, the thrust of the current work is to advance our understanding regarding the electronic communication in diporphyrins by probing meso – meso ‐bridged homo‐ and heterometallic diporphyrins.…”