화학공학소재연구정보센터
Inorganic Chemistry, Vol.52, No.3, 1248-1264, 2013
Effects of Sequence, Connectivity, and Counter Ions in New Amide-Linked Ru(tpy)(2)-Re(bpy) Chromophores on Redox Chemistry and Photophysics
New cationic metallo ligands L1-L3 based on bis(terpyridine) ruthenium(II) complexes decorated with differently substituted 2,2'-bipyridines attached via amide groups (5-NHCO-bpy, 4-CONH-bpy, 5-CONH-bpy) were prepared. Coordination of (ReCl)-Cl-I(CO)(3) fragments to the bpy unit gives the corresponding bimetallic Ru similar to Re complexes 1-3. Hydrogen bonds of the bridging amide groups to [PF6](-) counterions or to water molecules are observed both in the solid state and in solution. The impact of the amide orientation, the connecting site, and the coordination of counterions on redox and photophysical properties is explored. Both the metallo ligands L1-L3 and the bimetallic complexes 1-3 are emissive at room temperature in fluid solution. The emission originates from (MLCT)-M-3(Ru) states in all cases. Accordingly, the first oxidation of L1-L3 and 1-3 to [L1](+)-[L3](+) and [1]*-[3](+) is assigned to the Ru-II/III couple, while the first reduction to [L1](-)-[L3](-) and [1](-)-[3](-) occurs at the tpy-CO ligand as shown by UV/vis, IR, and EPR spectroscopy of the chemically generated radicals. Under rapid freezing conditions, radicals [2](-) and [3](-) are stabilized as different valence isomers with the odd electron localized at the [bpy-CO](center dot) bridging unit instead of the [tpy-CO](center dot). Furthermore, in radical [3](-) this valence equilibrium is shifted from [bpy-CO](center dot) to [tpy-CO](center dot) by coordination of [PF6](-) counterions to the bridging amide unit and back by replacing the [PF6](-) counterion with [BPh4](-). Photoinduced electron transfer (lambda(exc) = 500 nm) to L1-L3 and to 1-3 is successful using triethanolamine (TEOA) as a reducing agent. Photocatalytic reduction of CO2 by TEOA and 1-3 is hampered by the wrong site of electron localization in the one-electron reduced species [1](-)-[3](-).