Derivatives of dipyrido[3,2-a:2',3'-c]phenazine and its ruthenium complexes, influence of arylic substitution on photophysical properties

The synthesis and photophysical properties of a series of substituted dipyridophenazine (dppz) ruthenium complexes of the type (tbbpy)2Ru(dppz-R2)]2+ (where tbbpy = 4,4-tert-butyl-2,2-bipyridine and dppz = dipyrido3,2-a:2',3'-c]phenazine and R represents substitution at the 11 and 12 position with: Br, phenyl, 4-tert-butyl-phenyl and para-biphenyl) are described. The ligands could be obtained in high yields using Suzuki-type coupling reactions, an approach which also has been successfully applied to the analogous dppz-Br2 ruthenium complex. All compounds are fully characterised by NMR, MS and UV-vis spectroscopy. The solid state structures of dppz-bi-para-biphenyl and the ruthenium complex (tbbpy)2Ru(dppz-Br2)]2+ are also reported. The investigation of the free ligands reveals a pronounced effect of the arylic substitution on absorption and emission properties. These properties are mirrored in the corresponding complexes, which possess emission lifetimes of up to 900 ns. The resonance Raman investigation of the complex (tbbpy)2Ru(dppz-Br2)]2+ supports the assumption that the excited state properties of the substituted complexes are related to the parent (bpy)2Ru(dppz)]2+ compound, but that important differences may be expected based on the differences observed in the lowest energy absorption band.