Self-Assembled Light-Harvesting Systems: Ru(II) Complexes Assembled about Rh-Rh Cores.

Ru(II) polypyridine species were assembled about dirhodium(II,II) tetracarboxylate cores. The complexes prepd. have general formulas [{\{}(terpy)Ru(La){\}}n{\{}Rh2(CH3COO)4-n(MeCN)2{\}}]2n+ (a-type compds.: terpy = 2,2':6',2''-terpyridine; La = 4'-(p-carboxyphenyl)-2,2':6',2''-terpyridine; n = 1, 1a; n = 2, cis-2a and trans-2a (cis and trans refer to the arrangement of the Ru(II) species around the dirhodium core); n = 3, 3a), [{\{}(Lb)Ru(La){\}}n{\{}Rh2(CH3COO)4-n(MeCN)2{\}}]2n+ (b-type compds.: Lb = 6-phenyl-2,4-di(2-pyridyl)-s-triazine; n = 1, 1b; n = 2, an inseparable mixt. of cis-2b and trans-2b; n = 3, 3b; n = 4, 4b), and [{\{}(terpy)Ru(Lc){\}}{\{}Rh2(CH3COO)3(MeCN)2{\}}]2+ (1c; Lc = 6-(p-carboxyphenyl)-2,4-di(2-pyridyl)-s-triazine). As model species, also the mononuclear [(terpy)Ru(La)]2+ (5a), [(La)Ru(Lb)]2+ (5b), and [(terpy)Ru(Lc)]2+ (5c) were prepd. All of the complexes were characterized by several techniques, including NMR and mass spectra, and the stability of the various species is discussed. The absorption spectra of all of the compds. are dominated by the Ru(II) polypyridine moieties, showing intense ligand-centered (LC) bands in the UV region and intense metal-to-ligand charge-transfer (MLCT) bands in the visible. The compds. exhibit several metal-centered oxidn. and ligand-centered redn. processes, which were assigned to specific subunits. Both absorption and redox data indicate a supramol. nature of the assembled systems. Efficient energy transfer from the MLCT triplet state of the Ru-based components to the lowest-energy excited state of the dirhodium core takes place for the a-type compds. at 298 K in MeCN soln., whereas such a process is inefficient for the b-type and c-type species, which exhibit the typical MLCT emission. At 77 K in butyronitrile matrix, Ru-to-Rh2 energy transfer is partly efficient for both the a-type and the b-type compds. and is inefficient for 1c. The reasons for such behavior are discussed by taking into account arguments concerning the driving force and reorganization energy of the complexes. [on SciFinder(R)]


Soumis le 12 avril 2018