Transients in the flash photolysis of aqueous solutions of tris(2,2'bipyridine)ruthenium(II) ion

Aqueous solutions of Ru(bpy)/sub 3//sup 2 +/ (bpy = 2,2'-bipyridine) were flash photolyzed and pulse irradiated in the presence and in the absence of other additives. Hydrated electrons are produced in a process which is suggested to involve electron ejection from the first triplet of Ru(bpy)/sub 3//sup 2 +/, upon the absorption of a second photon. Most of the effective light (approximately 70%) was in the range 300 to 340 nm, while approximately 30% of the effective light was at wavelength >340 nm. The efficiency of e/sub aq/ production relative to the efficiency of production of the lowest triplet charge transfer state was measured under our conditions as 0.0015, independent of (Ru(bpy)/sub 3//sup 2 +/) and of flash intensity over a wide range. During our work on the biphotonic process for e/sup -//sub aq/ formation, a number of other reactions were investigated. Thus, hydrated electrons react with Ru(bpy)/sub 3//sup 2 +/ with a reaction rate constant of (5.8 +- 0.3) x 10/sup 10/ M/sup -1/s/sup -1/. The metal ions Zn/sup +/, Co/sup +/, and Cd/sup +/ reduce (Ru(bpy)/sub 3//sup 2 +/ with reaction rate constants (1.5 +- 0.2) x 10/sup 9/, (1.7 +- 0.2) x 10/sup 9/, and (6.1 +-more » 0.6) x 10/sup 8/ M/sup -1/ s/sup -1/, respectively, producing Ru(bpy)/sub 3//sup +/. Ru(bpy)/sub 3//sup +/ reacts with O/sub 2/, Cu/sup 2 +/, and duroquinone; the reaction rate constants are (7.2 +- 0.8) x 10/sup 9/, (3.4 +- 0.3) x 10/sup 8/, and (4.0 +- 0.5) x 10/sup 9/ M/sup -1/ s/sup -1/, respectively. The possibility for a biphotonic effect leading to H/sub 2/ formation is discussed.« less