Illuminating iron

Transition-metal complexes are used as photosensitizers and photocatalysts, and in light-emitting devices. For these uses, the complexes need to be excited from their ground state to a charge-transfer state, which generally needs to be long-lived to ensure efficient performance. This has made it challenging to replace the scarce but high-performing precious metals used in these complexes with Earth-abundant metals that are cheaper and less toxic. Pavel Chábera et al. now show that a design strategy that utilizes ligands with superior electronic properties yields iron complexes with unprecedented long-lived charge-transfer states. With further development, the approach could deliver iron-based materials for use as light emitters and photosensitizers in solar energy devices.