New RuII Scaffold for Photoinduced Ligand Release with Red Light in the Photodynamic Therapy (PDT) Window

: Four new RuII complexes, [Ru(tpy)(L)(CH3 CN]+ , where tpy=2,2':6',2"-terpyridine and L represents a series of acetylacetonate-based ligands, were synthesized for enhanced photoinduced ligand release with red light, λirr =655 nm. The metal-to-ligand charge transfer, 1 MLCT, transitions of these complexes are red-shifted and exhibit quantum yields of ligand dissociation that are five- to seven-fold greater than that of [Ru(tpy)(bpy)(CH3 CN)]2+ (bpy=2,2'-bipyridine), despite the absence of additional steric distortion. This series of complexes represents a new scaffold for drug photocaging and one of the first examples of RuII photocages that can release nitriles with light in the photodynamic therapy (PDT) window required for optimal tissue penetration.