Syntheses and Properties of Bimetallic Chromophore-Quencher Assemblies Containing Ruthenium(II) and Rhenium(I) Centers

We have prepared a family of six new bimetallic complexes containing electron-donating trans-{RuIICl(pdma)2}+ [pdma = 1,2-phenylenebis(dimethylarsine)] centers linked to trans-[RuIICl(pdma)(2,2‘-bpy)(NO)] (bpy = bipyridyl) or fac-{ReI(biq)(CO)3}+-based (biq = 2,2‘-biquinolinyl) electron acceptors.
The extended bridging units are based on 4,4‘-bpy or bpe [E-1,2-bis(4-pyridyl)ethylene] ligands, and
these assemblies are designed to display long-lived photoinduced charge-separated states. A number of
new monometallic precursor complexes have also been synthesized and fully characterized. The electronic
absorption spectra of the bimetallic species are dominated by intense, visible d(RuII) → π*(4,4‘-bpy/bpe)
metal-to-ligand charge-transfer (MLCT) bands and d(ReI) → π*(biq) absorptions in the near-UV region.
Cyclic voltammetric studies show both metal-based oxidation and ligand-based reduction processes
and provide evidence that these assemblies contain thermodynamic driving forces for charge separation.
Single-crystal X-ray structures have been determined for the monometallic complex salts fac-[ReI(biq)(CO)3(MeCN)]CF3SO3·CHCl3, fac-[ReI(biq)(CO)3(4-BrCH2C5H4N)]PF6, fac-[ReI(biq)(CO)3(4-HCO2CH2C5H4N)]PF6·Me2CO, fac-[ReI(biq)(CO)3(ISNE)]CF3SO3 (ISNE = ethylisonicotinate), and fac-[ReI(biq)(CO)3(NC5H4CO2)]2·HPF6·3MeCN. Ultrafast time-resolved infrared and Raman spectroscopic
measurements will be employed to investigate the photoexcitation properties of the bimetallic species
and of monometallic reference complexes.