Proton-Induced Tuning of Electrochemical and Photophysical Properties in Mononuclear and Dinuclear Ruthenium Complexes Containing 2,2‘-Bis(benzimidazol-2-yl)-4,4‘-bipyridine: Synthesis, Molecular Structure, and Mixed-Valence State and Excited-State Properties†

A series of mono- and dinuclear Ru(bpy)2 complexes (bpy = 2,2‘-bipyridine) containing 2,2‘-bis(benzimidazol-2-yl)-4,4‘-bipyridine (bbbpyH2) were prepared. The mononuclear complex [Ru(bpy)2(bbbpyH2)](ClO4)2·CH3OH·4H2O was characterized by an X-ray structure determination. Crystal data are as follows: triclinic, space group P1, a = 14.443(4) A, b = 15.392(4) A, c = 11.675(2)A, α = 101.44(2)°, β = 107.85(2)°, γ = 96.36(2)°, V = 2380(1) A3, Z = 2. The coordination geometry of the ruthenium(II) ion is approximately octahedral. The dihedral angle between the two pyridyl rings in bbbpyH2 is 9.4(3)°, which is close to coplanar, in the complex. Mono- and dinuclear complexes exhibit broad charge-transfer absorption bands at 420−520 nm and emission at 660−720 nm in CH3CN solution with lifetimes of 200−800 ns at room temperature. Transient difference absorption spectra and resonance Raman (rR) spectra were used to assign the charge-transfer bands in the 420−520 nm region and to identify the lowest excited states. Bo...