Photochemical Tuning of Tris-Bidentate Acridine- and Phenazine-Based Ir(III) Complexes.

Five new Ir(III) complexes of the type [Ir(ppy)2L]+ (where ppy = 2-phenylpyridine, L = bidentate N^N ligand) bearing linear and elbow-shaped acridine- and phenazine-based extended planar aromatic ligands have been successfully synthesized and characterized. The electrochemical and photochemical studies revealed that all complexes allow emission in the range 589-601 nm from excited states corresponding to a charge transfer between an Ir-ppy fragment and the extended planar ligand. Luminescence quenching occurs in water for [Ir(ppy)2dpac]+ (Ir-DPAC), [Ir(ppy)2dpacF2]+ (Ir-DPACF 2 ), [Ir(ppy)2dpacF4]+ (Ir-DPACF 4 ) and [Ir(ppy)2bdppz]+ (Ir-BDPPZ), while solely partial quenching is observed for [Ir(ppy)2npp]+ (Ir-NPP). This "light-switch" effect has been ascribed to the possible formation of a non-emissive mono-hydrogen-bonded excited state for the four complexes. The "elbow shaped" of Ir-NPP is believed to prevent the non-chelating nitrogen atom of the npp ligand to form H-bond with solvent molecules. The results emphasized the potential of small chemical modifications of the extended planar ligand on the properties of the corresponding Ir(III) complexes. Their tunable properties make them ideal candidates for applications such as DNA photoprobes.