Previously, we have reported observing photoinduced elec-tron-transfer reactions on exciting the low-lying metal-to-ligand charge-transfer excited state (s) of bis (2, 9-dimethyl-1, 10-phenanthroline) copper (I) in aqueous solutionscontaining various Co (III) substrates. 1" 3 We have also reported that the same complex, which is denoted Cu (dmp) 2+, exhibits charge-transfer emission in CH2C12 solution at room tem-perature and that the emission is dynamically quenched by a series of nitroaromatic molecules as well as tris (acetylacetonato) cobalt (III). 4 Because of the profound solvent effects that have been observed for this system, 3, 4 it is difficult to relate these results directly, but both types of experimental observations can be understood in terms of a reactive charge-transfer excited state that is strongly reducing. 5 The chemical and physical properties of such charge-transfer states have been of considerable interest recently. One reason is that they mayprove useful in energy conversion processes. 6" 8 From a more fundamental point of view, they can be used as novel reagents in studies of electron-transfer reactions, par-ticularly those involving large driving forces. 910 In the par-ticular case of copper (I) the development of luminescence spectroscopy holds promise because of the dearth of convenient spectroscopic handles available. The method may be especially important in studies of copper-containing proteins where several interesting luminophores have recently been de-scribed. 11" 13 For these various reasons we have continued our studies of