Prompt and delayed photoejection of hydrated electrons in the UV photolysis of aqueous solutions of copper(I) complexes

Chemical Scavenging Yields for Short-Lived Products from the Visible Light Photoionization of the Tris(bipyridine)ruthenium(II) Triplet Metal-to-Ligand Charge-Transfer Excited State

The rate of visible light photoionization of the tris(bipyridine)ruthenium(II) triplet metal-to-ligand charge-transfer excited state (³MLCT) is very strongly dependent on the acid concentration in aqueous solution, and the pattern of this dependence is similar to that reported for the photoionization of iodide. With 405 nm visible irradiation of ³MLCT, less than 15% of the photoionized products appear as free solvated electrons in bulk solution, while more than 75% of the photoproducts appear to be solvent-separated, (oxidized substrate)-electron ion pairs that efficiently recombine with the photo-oxidized complex in the absence of an electron scavenger. The quantum yield of free solvated electrons generated by these 405 nm irradiations is approximately 0.004, but the net quantum yield of scavengeable electrons is estimated to be about 0.04. A visible-region photoionization threshold energy for the ³MLCT is consistent with thermodynamic expectations, and similar behavior is expected for many redox-active complexes.

Formation and photoinduced electron ejection of amminedicyanocuprate(I) and cyano-bridged trinuclear copper(I) complexes in aqueous ammonia solution

UV absorption spectral evidence confirms that a mixed-ligand complex, Cu(CN)(2)(NH(3))(-), is formed in an aqueous solution of KCu(CN)(2) and ammonia. The stepwise stability constant for the reaction, Cu(CN)(2)(-) + NH(3) = Cu(CN)(2)(NH(3))(-), is 2.80 +/- 0.40 in 1 M ionic strength, NaClO(4) medium at 25 degrees C. This amminedicyanocuprate(I) ion readily combines in aqueous solution in a 1:2 and 2:1 molar ratios with Cu(NH(3))(2)(+) to form two trinuclear ionic species, presumably with cyano bridges, with the suggested formulas of Cu(3)(CN)(2)(NH(3))(5)(+) and Cu(3)(CN)(4)(NH(3))(3)(-). The resolved UV absorption spectra of the monomer and two trimers have been determined and exhibit strong bands, presumably metal-ligand charge transfer in nature, in the 200-250-nm region. When solutions of all three complexes absorb a pulse of 266-nm laser light, they photoeject hydrated electrons monophotonically, with quantum yields of 0.41 +/- 0.02, 0.53 +/- 0.02, and 0.50 +/- 0.01 for the monomer, cationic trimer, and anionic trimer, respectively, suggesting that absorption in the charge-transfer-to-solvent bands of these complexes results in an efficient electron ejection process that is enhanced by the existence of a polynuclear structure with cyano bridges. No room-temperature luminescence is observed for these complexes.