Development Novel Photosensitiser Materials Based on Earth-Abundant Elements

Photophysical sensitiser materials based on metals such as ruthenium and iridium offer superb performance and avenues for tuning and optimisation of their properties. However, it is a far from simple task to substitute these rare and expensive elements by cheaper and more-abundant first row transition metal elements. The metal-to-ligand charge transfer (MLCT) states that are responsible for the attractive properties of ruthenium(II) d6 complexes are rapidly deactivated in their low-spin d6 iron(II) analogues by metal-centred (MC) states that are much lower lying than for ruthenium and also high-spin states that are inaccessible for ruthenium. A typical approach to remedy this situation has relied upon increasing the donor strength of ligands to increase the d-orbital splitting and raise the energies of these deleterious MC states. However, this approach has only had limited success.

In what is a current and extremely hot area in modern inorganic chemistry there has been a move away from attempting to force iron(II) to behave like ruthenium(II) and instead explore alternative electronic configurations of complexes of lighter elements and exploit their own unique photophysical properties. This has led to materials based on d5 Fe(III), d3 Cr(III) and d0 Zr(IV) that exhibit excited states of different electronic character to traditional MLCT states, have record lifetimes and have potent photocatalytic properties.

In this project the development of new photosensitiser materials based on lighter Earth-abundant metals will be targeted. This will involve the synthesis of new ligands and their complexes. The photophysical and electrochemical properties of the resultant materials will be thoroughly characterised by steady state methods. In collaboration with world-leading national and international partners materials will also be investigated by ultrafast transient absorption spectroscopy methods with work supported by computational chemistry calculations. Guided by end user needs the synthetic design of complexes will be informed by, and ultimately used to mediate challenging photocatalytic organic transformations and polymerisation reactions.