Extending the light-harvesting properties of transition-metal dendrimers.
We report a study of the electronic energy-transfer dynamics within the transition-metal polypyridine complex OsRu3pyr6 (Os[(dpp)Ru(bpy{pyrene})2]3(8+), where dpp=2,3-bis(2'-pyridyl)pyrazine and bpy=2,2'-bipyridine) after excitation with UV light. By using a broadband visible femtosecond probe, we are able to simultaneously detect both the energy transfer from the peripheral aromatic ligands to the Os center and the sub-picosecond energy transfer from the initially excited Ru-bpy ligand-centered state to the Os triplet metal-to-ligand charge-transfer (MLCT) state. Pyrene energy transfer occurs from both the nonrelaxed and the relaxed S(1) states on timescales of 6 and 45 ps, respectively. In both cases, the energy transfer is described by means of Förster energy transfer theory. Sub-picosecond energy transfer within the OsRu3 metal-ligand core most likely includes a direct energy transfer between the higher-lying ligand-centered states on Ru and Os, in addition to the transfer between the MLCT states. The absorption cross-sections in both the UV and the visible spectral regions are enhanced by attaching the aromatic pyrene ligands. Furthermore, energy transfer is directed only towards the Os core, which ultimately leads to an exclusive population of the Os-based triplet MLCT state, thus making the OsRu3pyr6 transition metal-polypyridine dendrimer an obvious candidate for artificial light-harvesting systems.
Department of Chemical Physics, Lund University Box 124, SE-221 00 Lund, Sweden.
Jane
J
Larsen
Fausto
F
Puntoriero
Torbjörn
T
Pascher
Nathan
N
McClenaghan
Sebastiano
S
Campagna
Eva
E
Akesson
Villy
V
Sundström
D002627:Chemistry, Physical / Q000379:methods; D050091:Dendrimers / Q000737:chemistry*; D004735:Energy Transfer; D007700:Kinetics; D008027:Light; D008670:Metals / Q000737:chemistry*; D015233:Models, Statistical; D008968:Molecular Conformation; D015394:Molecular Structure; D010777:Photochemistry / Q000379:methods*; D013053:Spectrophotometry / Q000379:methods; D028561:Transition Elements / Q000737:chemistry*; D014466:Ultraviolet Rays
D050091:Dendrimers; D008670:Metals; D028561:Transition Elements