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MODULATION OF VISIBLE ABSORPTION PROPERTIES IN NEW RUTHENIUM POLYPYRIDYL COMPLEXES BY INTRODUCING MIXED LIGANDS WITH STRONG ELECTRON DONOR AND STRONG ELECTRON ACCEPTOR GROUPS
CATTANEO, MAURICIO.; FAGALDE, FLORENCIA; KATZ, NÉSTOR E
Simposio; 6th Latin American Symposium on Coordination and Organometallic Chemistry; 2017
ACS, CONICET, Alexander von Humboldt, Royal Society of Chemistry
Two new ruthenium complexes, containing 2,2?- bipyridines with substituentsof very different electron accepting abilities, of formula[Ru(4,4?dmobpy)2(4,4?-dcabpy)]2+ (1) and [Ru(4,4?-dmobpy)(4,4?-dcabpy)2]2+ (2), where 4,4?-dmobpy = 4,4?-dimethoxy-2,2?-bipyridine and 4,4?-dcabpy =2,2?-bipyridine-4,4?-dicarboxylic acid, were synthesized as PF6- salts andcharacterized by spectroscopic, electrochemical and photophysicaltechniques. In both complexes, two intense bands are observed in the visibleregion, which can be assigned to MLCT transitions dπ (Ru) → π*(4,4?-dmobpy) and dπ (Ru) → π*(4,4?-dcabpy), the latter being the lowest energyone, as expected from the strong electron accepting properties of 4,4?-dcabpy. The energy separation between both bands is higher in (1) than in(2), due to the introduction of a higher number of electron donor ligands(4,4?-dmobpy) in the former species. Base titration of the carboxylic acidgroups by absorption and emission measurements shows that the excitedstates are stronger bases than the ground states in (1). Respect to similarcomplexes previously reported,1 further absorption and emission into the NIRis disclosed, since the energy of the lowest-lying LUMO levels decreaseswhen introducing strong electron donor substituents in the non-protonablebipyridyl ligands. These spectral changes are relevant to improve theperformance of dye-sensitized solar cells.