Ultrafast Ligand Exchange: Detection of a Pentacoordinate Ru(II) Intermediate and Product Formation

The ultrafast kinetics of ligand exchange of cis-Ru(bpy)(2)(CH(3)CN)(2)(2+) were measured in H(2)O and CH(3)CN. The formation of the (3)MLCT excited-state and a five-coordinate intermediate are observed in both solvents within 2 ps after excitation (310 nm, fwhm approximately 300 fs). The (3)MLCT excited-state undergoes vibrational cooling (5-6 ps), then decays to regenerate the ground-state with a lifetime of approximately 50 ps. In CH(3)CN, ligand recombination takes place in 28 ps, while the formation of cis-Ru(bpy)(2)(CH(3)CN)(H(2)O)(2+) in H(2)O takes place with tau = 77 ps.