title: Ultrafast photo-induced ligand solvolysis of cis-[Ru(bipyridine)2(nicotinamide)2](2+): experimental and theoretical insight into its photoactivation mechanism.
abstract: Mechanistic insight into the photo-induced solvent substitution reaction of cis-[Ru(bipyridine)2(nicotinamide)2](2+) (1) is presented. Complex 1 is a photoactive species, designed to display high cytotoxicity following irradiation, for potential use in photodynamic therapy (photochemotherapy). In Ru(II) complexes of this type, efficient population of a dissociative triplet metal-centred ((3)MC) state is key to generating high quantum yields of a penta-coordinate intermediate (PCI) species, which in turn may form the target species: a mono-aqua photoproduct [Ru(bipyridine)2(nicotinamide)(H2O)](2+) (2). Following irradiation of 1, a thorough kinetic picture is derived from ultrafast UV/Vis transient absorption spectroscopy measurements, using a 'target analysis' approach, and provides both timescales and quantum yields for the key processes involved. We show that photoactivation of 1 to 2 occurs with a quantum yield ≥0.36, all within a timeframe of ~400 ps. Characterization of the excited states involved, particularly the nature of the PCI and how it undergoes a geometry relaxation to accommodate the water ligand, which is a keystone in the efficiency of the photoactivation of 1, is accomplished through state-of-the-art computation including complete active space self-consistent field methods and time-dependent density functional theory. Importantly, the conclusions here provide a detailed understanding of the initial stages involved in this photoactivation and the foundation required for designing more efficacious photochemotherapy drugs of this type.
authors: Department of Chemistry, University of Warwick, Library Road, Coventry, CV4 7AL, UK. v.stavros@warwick.ac.uk g.m.roberts@bristol.ac.uk.
authors: Simon E
authors: SE
authors: Greenough
authors: Gareth M
authors: GM
authors: Roberts
authors: Nichola A
authors: NA
authors: Smith
authors: Michael D
authors: MD
authors: Horbury
authors: Russell G
authors: RG
authors: McKinlay
authors: Justyna M
authors: JM
authors: Żurek
authors: Martin J
authors: MJ
authors: Paterson
authors: Peter J
authors: PJ
authors: Sadler
authors: Vasilios G
authors: VG
authors: Stavros
mesh_terms: D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D015394:Molecular Structure; D055668:Photochemical Processes; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry
chemical_list: D056831:Coordination Complexes; D008024:Ligands; D012997:Solvents; C000597714:cis-(Ru(bipyridine)2(nicotinamide)2)(2 )