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

Abstract

Four new Ru^II 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, λ_irr =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 Ru^II photocages that can release nitriles with light in the photodynamic therapy (PDT) window required for optimal tissue penetration.