Formation of electronically excited products in electron-transfer reactions: reaction of polypyridine complexes of cobalt(I) and ruthenium(III) in acetonitrile

The yields of the metal-to-ligand charge-transfer excited state of poly(pyridine)ruthenium(II) complexes (*RuL/sub 3//sup 2 +/) produced in the reaction of RuL/sub 3//sup 3 +/ with poly(pyridine)cobalt(I) complexes in acetonitrile have been measured by use of a combination of continuous flow methods and chemical actinometry. The *RuL/sub 3//sup 2 +/ yields are high, ranging from 0.31 +/- 0.04 for the most exergonic system (Ru(bpy)/sub 3//sup 3 +/ and Co(4,4'-(CH/sub 3/)/sub 2/bpy)/sub 3//sup +/) to 0.07 +/- 0.02 for the least exergonic system studied (Ru(4,7-(CH/sub 3/)/sub 2/phen)/sub 3//sup 3 +/ and Co(bpy)/sub 3//sup +/. The results are interpreted in terms of competing electron-transfer channels yielding primarily *RuL/sub 3//sup 2 +/ + CoL/sub 3//sup 2 +/ and RuL/sub 3//sup 2 +/ + *CoL/sub 3//sup 2 +/(/sup 2/T), with the formation of entirely ground-state products being negligible. A new actinometer consisting of Os(terpy)/sub 2//sup 2 +/ and Co(NH/sub 3/)/sub 5/Cl/sup 2 +/, for use at wavelengths up to approx.720 nm, is described.