Application of Discrete First‐Row Transition‐Metal Complexes as Photosensitisers

Abstract

This Minireview summarises and critically evaluates recent advances in the utilisation of discrete first‐row transition‐metal (TM) complexes as photosensitisers. Whilst many compounds absorb light, TM complexes are generally more desirable for photochemical applications, as they usually exhibit strong absorption of visible light, making them ideally suited to exploiting the sun as a freely available light source. Due to their outstanding activities, precious metals, such as iridium and ruthenium, are currently still at the forefront of photochemistry research. However, they also bear disadvantages with respect to abundance, cost and toxicity. Therefore, it is desirable to move to more abundant and less expensive systems that retain good photosensitising abilities. This Minireview will focus on first‐row transition‐metals, specifically titanium, copper, iron, and zinc, which have become the focus of increased attention over recent years as potential replacements for noble metals as photosensitisers. Their structure – activity relationships are explored and challenges in designing the ligands and complexes are discussed.

Phototherapeutic anticancer strategies with first-row transition metal complexes: a critical review

“…21 One can also think that a mercury-containing complex, namely thiomersal, is used as a preservative for vaccine. 22 A comprehensive mini-review from Behm and McIntosh gives a great perspective of the use, and associated challenges, of first-row transition metal complexes as PSs, although not specifically for applications in PDT or PACT, 23 which is the focus of the present review. First-row transition metals display characteristics that can prove challenging for photochemical endeavors.…”

Comprehensive Picture of the Excited State Dynamics of Cu(I)- and Ru(II)-Based Photosensitizers with Long-Lived Triplet States

“…The first step in typical photocatalytic cycles is the excitation of a photosensitizer by the absorption of a photon. , While traditionally applied, photosensitizers are often based on noble 4d and 5d metals, especially those with a low-spin d 6 configuration. ,− Research is currently aiming to overcome these rare and expensive metals. To achieve this goal, photocatalytic systems are being developed, that rely on organic chromophores , or more abundant 3d metals. − Especially heteroleptic Cu­(I) complexes, consisting of a diphosphine and a diimine ligand, can combine the key properties of long excited state lifetimes and high quantum yields. ,− They also demonstrated their capacity to outperform their Ir­(III)- and Ru­(II)-based competitors in certain photocatalytic applications. − …”

“…As the development of noble metal free photosensitizers is of great interest, ,,, we aimed for the preparation of the related heteroleptic Cu­(I) complex [(xant)­Cu­(biipo)]­PF 6 ( Cubiipo ) with xant = xantphos (Figure ).…”

Merging of a Perylene Moiety Enables a RuII Photosensitizer with Long‐Lived Excited States and the Efficient Production of Singlet Oxygen

“…[3][4][5] In this context, the efficient absorption and storage of photonic energy by a suited photosensitizer is crucial. In fact, especially the photosensitizer plays a key role in every photocatalytic system [6][7][8][9] and in diverse applications like organic light-emitting diodes (OLEDs), [10,11] dye-sensitized solar cells (DSSCs) [12,13] or in photodynamic therapy (PDT). [14,15] For these applications, transition metal complexes based on polypyridine ligands are still frequently used.…”