Unveiling new horizons: Exploring rhenium and iridium dipyrrinato complexes as luminescent theranostic agents for phototherapy

Luminescent dipyrrinato complexes of d-block metals are well explored in literature for diverse applications in materials as well as in biology. They offer exceptional fine tuning of their electrochemical and optical properties with the variety of substitutions on the dipyrrin core. The development of mixed ligand type dipyrrinato complexes with heavy metals like: Ru, Os, Pd, Pt, Re, Ir are of great interest in biomedical applications due to significant ROS (Reactive Oxygen Species) generation, anti-microbial and anti-cancer applications. Such dipyrrinato complexes display bright triplet emission in the visible to red region due to heavy atom effect. This review is focused on the synthesis of luminescent dipyrrinato complexes of Re(I) and Ir(III) with different types of co-ligands around the metal center. The overviewed complexes are subcategorized further on the basis of metal and substitutions on the dipyrrin C-5 position or around the metal center. Re and Ir complexes of subporphyrin, N-confused porphyrin, sapphyrin, rubyrin and N-fused porphyrins have also been included. Their absorption and emission properties and their ability to work as triplet photosensitizers are discussed. Deliberations are made to understand their potential as cellular imaging agents and/or photosensitizers for ROS generation and phototherapy to treat cancer.