Transition metal dipyrromethenes: Seeking alternatives to BODIPY dyes

This review describes recent advances in the coordination chemistry of transition metal ions with a variety of 2,2′-dipyrromethene bidentate ligands. A brief history of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes and the role of the BF 2 moiety is presented. Substituting transition metal cations for BF 2 adds complexity expressed by partially filled d-orbitals, multiple coordination numbers and geometries, and numerous accessible oxidation states. The spectroscopic, magnetic, and electrochemical properties of a variety of transition metal dipyrrins and their applications as catalysts, light harvesting, and phototherapeutic complexes are described.