Ultrafast photo-induced ligand solvolysis of cis-[Ru(bipyridine)(2)(nicotinamide)(2)](2+): experimental and theoretical insight into its photoactivation mechanism

Simon E. Greenough, Gareth M. Roberts, Nichola A. Smith, Michael D. Horbury, Russell G. McKinlay, Justyna M. Zurek, Martin J. Paterson, Peter J. Sadler, Vasilios G. Stavros

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Abstract

Mechanistic insight into the photo-induced solvent substitution reaction of cis-Pu(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(m) complexes of this type, efficient population of a dissociative triplet metal-centred ((MC)-M-3) 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.

Original languageEnglish
Pages (from-to)19141-19155
Number of pages15
JournalPhysical Chemistry Chemical Physics
Volume16
Issue number36
DOIs
Publication statusPublished - 2014

Keywords

  • RUTHENIUM POLYPYRIDYL COMPLEXES
  • DENSITY-FUNCTIONAL THEORY
  • EXCITED-STATE EVOLUTION
  • LIGHT-EMITTING DEVICES
  • PHOTOSUBSTITUTION REACTIONS
  • PHOTOCHEMICAL DISSOCIATION
  • CONICAL INTERSECTIONS
  • PHOTODYNAMIC THERAPY
  • FEMTOSECOND DYNAMICS
  • RELAXATION DYNAMICS

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