New Light-Harvesting Molecular Systems Constructed with a Ru(II) Complex and a Linear-Shaped Re(I) Oligomer

A novel type of light-harvesting complexes was synthesized with a linear-shaped Re(I) oligomer as a photon absorber and a Ru(II) polypyridyl complex as an energy acceptor. The Re(I) oligomer and the Ru(II) complex are connected to each other with a bisdiimine ligand, that is, 1,2-bis[4-(4'-methyl-2,2'-bipyridinyl)]ethane (C2dmb). These Ru(II)-Re(I) multinuclear complexes, [Ru(dmb)(2)(C2dmb)Re(CO)(2)-{-PP-Re(dmb)(CO)(2)-PP-Re(dmb)(CO)(3)}(2)](PF6)(7), [Ru(dmb)(2)(C2dmb)Re(CO)(2){-PP-Re(dmb)(CO)(3)}(2)](PF6)(5), and [Ru(dmb)(2)(C2dmb)Re(CO)(3)-PP-Re(dmb)(CO)(2)-PP-Re(dmb)(CO)(3)](PF6)(5) (dmb = 4,4'-dimethyl-2,2'-bipyridine; PP = bis(diphenylphosphino)acetylene), can strongly absorb a wide range of UV-vis light and emit mostly from the (MLCT)-M-3 excited state of the Ru(II) unit at room temperature in solution even when the Re chain absorbs the light. Comparison of their photophysical properties with those of the corresponding model complexes shows that a highly efficient energy transfer from the Re chain to the Ru(II) unit occurs, and the energy transfer rate constants from each Re(I) unit were determined.