Transient midinfrared study of light induced dissociation reaction of Ru(dcbpy)(CO)2I2 in solution

Illumination of Ru(dcbpy)I-2(CO)(2) (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) with (near) ultraviolet light induces dissociation of one of the CO groups of the complex. In solution the opened coordination site of the metal is occupied by a solvent molecule. In the present study the kinetics of the ligand exchange reaction has been studied in solution with femtosecond time resolution by probing the CO stretching vibrations of the reactant and the product molecules Ru(dcbpy)I-2(CO)(EtOH) in the infrared and probing electronic transitions in the visible spectral regions. The kinetic results indicate that photoelimination of the CO group occurs on a subpicosecond time scale. The overall quantum yield of the reaction is well below unity (0.3), indicating that the majority of the excited parent molecules does not convert to the product molecules. According to the present observations, recovery of the parent molecule takes place on a subpicosecond time scale. Later time evolution shows relaxation of this state with time constants of 4 and 68 ps. Dissipation of the excess energy of the solvated product is characterized by a biexponential relaxation process with time constants of 18 and 270 ps.