Pushing the limits of structurally-diverse light-harvesting Ru(II) metal-organic chromophores for photodynamic therapy
•We establish a synthetic routs for metal-organic Ru(II) compounds, [(AnthbpyMe)(bpy)Ru(dpp)](PF6)2 and [(AnthbpyMe)2Ru(dpp)](PF6)2, and analyze their excited state properties.•We examine the interchromophoric communication upon excitation of the anthracene and Ru(II) subunits to establish potential deactivation pathways.•The complexes were shown to be moderately cytotoxic towards F98 rat glioma cells in the dark, an effect that was substantially enhanced upon illumination with visible light.
The synthesis of Ru(II) derivatives [(AnthbpyMe)(bpy)Ru(dpp)]2+ (2) and [(AnthbpyMe)2Ru(dpp)]2+ (3), and the analysis of their excited state properties as well as their photocytotoxicity against glioma cells are reported. Complexes 2 and 3 absorb visible light with metal-to-ligand charge transfer (MLCT) transitions at λmax = 459 nm (16,000 M−1 cm−1) and λmax = 461 nm (21,000 M−1 cm−1), respectively. The complexes exhibit bichromatic properties with the 3MLCT emission centered at λem = 661 nm and λem = 663 nm for 2 and 3, respectively, while the anthracene motif(s) has emission from 450–560 nm. The anthracene unit(s) quench the 3MLCT to give quantum yields (lifetime, τ) of Φem = 0.0059 (τ = 398 ns) and Φem = 0.0011 (τ = 414 ns) for 2 and 3, respectively. The quenching rates were found to be 6.61 × 105 s−1 for 2 and 5.64 × 105 s−1 for 3. Electrochemistry reveals an irreversible anthracene oxidation at 1.23–1.28 V, while the RuIII/II oxidation process occurs at a potential of 1.53–1.55 V. The complexes displayed a quasi-reversible reduction couple attributed to dpp0/−1 at 0.98 V. Cytotoxicity of both complexes towards F98 glioma cells was moderate in the absence of light and substantially enhanced with visible light.
Graphical abstractAnthracene fluorophores were attached to Ru(II) based complexes that demonstrate promise as agents for photodynamic therapy in order to probe of their uptake into, distribution within, and effects on, the viability of mammalian cells. These molecules exhibit dynamic excited state properties and enhanced PDT potency against highly invasive and aggressive forms of brain cancer.Figure optionsDownload full-size imageDownload as PowerPoint slide
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volumes 322–323, 15 May–1 June 2016, Pages 67–75