Dinuclear ruthenium(II) polypyridyl complexes containing large, redox-active, aromatic bridging ligands: Synthesis, characterization, and intramolecular quenching of MLCT excited states

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-/:2''',3'''-n]pentacene (tatpp) and 9,11,20,22-tetraazatetrapyrido[3,2-a:2'3'-c: 3,2-/:2''',3'''-n]pentacene-10,21-quinone (tatpq) have been synthesized and characterized by H-1 and C-13 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.