Dinuclear Ruthenium(II) Polypyridyl Complexes Containing Large, Redox-Active, Aromatic Bridging Ligands: Synthesis, Characterization, and Intramolecular Quenching of MLCT Excited States

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Abstract
Two new ruthenium(II) polypyridyl dimers containing the large planar aromatic bridging ligands 9,11,20,22-tetraazatetrapyrido[3,2-a:2‘3‘-c:3‘ ‘,2‘ ‘-l:2‘ ‘‘,3‘ ‘‘-n]pentacene (tatpp) and 9,11,20,22-tetraazatetrapyrido[3,2-a:2‘3‘-c:3‘ ‘,2‘ ‘-l:2‘ ‘‘,3‘ ‘‘-n]pentacene-10,21-quinone (tatpq) have been synthesized and characterized by 1H and 13C NMR, MALDI mass spectrometry, and elemental analyses. The electronic properties (UV−vis, redox, photophysical) of these dimers are analyzed in the context of orbital calculations (PM3 level) on the bridging ligands. A localized orbital model is proposed in which low-lying acceptor orbitals on the center portion of the ligands effectively quench the Ru(II)-based MLCT emission via a mechanism that can be viewed as intramolecular electron transfer to specific subunits of the bridges.