Picosecond Flash Photolysis of Carbonyl Complexes of Ruthenium(II) porphyrin pi-Cation Radicals
Barley, M., David Dolphin, James, B.R., Kirmaier, C., and Holten, D.
J. Am. Chem. Soc.
Picosecond transient absorption technique was used to study photolysis of the Ru(II) octaethylporphyrin π-cation radicals Ru(OEP)+.CO(L) [I: L = EtOH; II: L = pyridine; III: L = imidazole; IV: L = Br-]. Excitation with 35-ps flashes at 532 nm resulted in the formation and decay of transient states having lifetimes less than the flash duration. The transient lifetimes for 2A1u ground-state π cation radicals were shorter than those observed after excitation of species with the 2A2u ground state. The transient behavior was rationalized in terms of both release of CO followed by rapid geminate recombination, and of rapid radiationless decay via nondissociative states. Low-lying (d,π) charge-transfer states of the π cation radicals provided effective routes for deactivation. Photolysis with 355-nm flashes resulted in the formation of similar short-lived transients. However, in the case of I and II, having mainly the 2A2u ground state, a longer-lived photoproduct was observed. The quantum yield of the photoproduct was <25%.