Ruthenium(II) Dendrimers Containing Carbazole-Based Chromophores as Branches

• DOI: 10.1021/ja021373y
• Publication Date: 2003-04-30T04:56:21Z
• Authors: Nathan D. McClena...; Rosalba Passalacqua; Frédérique Loiseau; Sebastiano Campagna; Bert Verheyde; Ahmed Hameurlaine; Wim Dehaen
• Keywords: Carbazole; Chromophore

Three new luminescent and redox-active Ru(II) complexes containing novel dendritic polypyridine ligands have been synthesized, their absorption spectra, luminescence properties (both at room temperature in fluid solution 77 K rigid matrix), redox behavior investigated. The are made of 1,10-phenanthroline coordinating subunits carbazole groups as branching sites. first second generation species this class (L1 L2, respectively; see Figure 1 for structural formulas) prepared employed. metal dendrimers investigated [Ru(bpy)(2)(L1)](2+) (1; bpy = 2,2'-bipyridine), [Ru(bpy)(2)(L2)](2+) (2), [Ru(L1)(3)](2+) (3; 2). For the sake completeness comparison purposes, also behavior, L1 L2 studied, together with 3,6-di(tert-butyl)carbazole (L0) [Ru(bpy)(2)(phen)](2+) (4, phen 1,10-phenanthroline). spectra free show features which can be assigned to various (i.e., phenanthroline groups) additional bands lower energies (at lambda > 300 nm) carbazole-to-phenanthroline charge-transfer (CT) transitions. These latter significantly red-shifted upon acid and/or zinc acetate addition. Both exhibit relatively intense (lifetimes nanosecond time scale, quantum yields order 10(-2)-10(-1)) matrix millisecond scale). Such a is CT states phenanthroline-centered pi-pi triplet levels K. room-temperature totally quenched by or acetate. typical complexes. In particular, metal-to-ligand (MLCT) dominate visible formally MLCT govern excited-state properties. Excitation spectroscopy evidences that all light absorbed branches transferred unitary efficiency 1-3, showing regarded efficient light-harvesting antenna systems. All rich (except 3, whose was not because solubility reasons), clearly attributable reversible carbazole- metal-centered oxidation polypyridine-centered reduction processes. electronic interaction between sites affected coordination.