Molecular design and properties of near-infrared emitting Cr(III) complexes

The development of highly-emissive nonprecious metal complexes is an effective strategy toward low-cost photochemistry and efficient utilization of natural resources. Among them, near-infrared emitting Cr(III) complexes possess the potential as an excellent photofunctional material with high emission quantum yield and long lifetime. In recent years, significant development has been made in the development of photofunctional Cr(III) complexes by the use of tridentate ligands with a large bite angle. In this manner, highly-efficient spin-flip near-infrared emission and circularly polarized luminescence of chiral Cr(III) complexes have been achieved. The molecular design and near-infrared emissions of these Cr(III) complexes are discussed in this review, together with their current research state and remaining issues. Finally, potential strategies to improve the luminescent properties of achiral and chiral Cr(III) complexes are proposed.