Characteristic of our group’s evolving strategies in the design of metal complexes for tailored biological applications e.g. photodynamic therapy (PDT) [1] we hereby share insights into the unusual photophysics and cytotoxity of two novel complex families. These have in common ligands that are built around a bipyridine-ethynyl-chromophore motif.
The first of the two families was created using an ‘on-the complex’ synthetic approach and involves Nile Red (NR) as an intensely absorbing lipophilic chromophore[2]. Given its desirable photophysical properties (λex 610 nm, ΦΔ 90.4% and possessing a non-emissive triplet state capable of singlet oxygen generation) the Ru(II)-3ENR complex was expected to be a potent photosensitiser (PS) in PDT experiments. It was drammatically out-performed however (approximately 2-fold) by its Ir(III)-ENR analogue which in comparison had a much lower ΦΔ (λex 610 nm, ΦΔ 9.7 %). We present here our collaborative efforts to understand to what extent this is due to better internalisation of the Ir(III) complex by the SKBR-3 cells and/or alternative oxygen-independent mechanisms of action.
The second family of complexes were accessed using an unusual convergent synthetic route comprises unsymmetrical bipyridine ligands with conventional donor/acceptor moieties. These materials demonstrate solvent-dependent excited state switching and ground state energies that are influenced by the counter-ion. These systems have moderate dark cytotoxicty and preliminary in vitro cell studies show that despite their simplicity they are very efficient at generating Reactive Oxygen Species (ROS).