Quenching reactions of the phosphorescent state of Ru(bpydc)(3)(4-) by a cationic ion, Co(bpy)(3)(3+), Co(phen)(3)(3+), co(tpy)(2)(3+), and methyl viologen (MV2+) to yield ET products were examined for the aqueous solutions by means of transient absorption kinetic spectroscopy and time-correlated single photon counting technique. A molecular complex formed in the ground state, [Ru(bpydc)(3)(4-) . . . Co(tpy)(2)(3+)], produces ET-products in the bulk with a small fraction of 0.3 on the photoexcitation, The fractions of ET product formation in the collisional quenching by Co(tpy)(2)(3+) (0.43) is lower than the re-dissociation fraction (0.71) of an encounter complex, Ru(bpydc)(3)(3-)-Co(tpy)(2)(2+), for the reverse ET reaction. A process to reduce the formation of a cage-complex of [Ru(bpydc)(3)(3-) . . . Co(tpy)(2)(2+)], in the collisional quenching is the conversion of unrelaxed cage-complex to the original reactant pair, [Ru(bpydc)(3)(4-) . . . Co(tpy)(2)(3+)] via a potential intersect between the potential energy surfaces (PES) (avoid crossing). Such rapid a deactivation process is suggested by a lower fraction of ET-product formation (0.06) in the bimolecular quenching of Ru-3(bpydc)(3)(4-) by MV2+ than the re-dissociation 31 fraction (0.18) of the encounter complex for the reverse ET reaction. Both Co(bpy)(3)(3+) and Co(phen)(3)(3+), which do not form a molecular complex with Ru(bpydc)(3)(4-) in the ground state, produce ET-products in the collisional quenching of Ru-3(bpydc)(3)(4-) and Ru-3(bpy)(3)(2+) with a high fraction (0.93-1.0). The re-dissociation fractions of the encounter complex for the reverse ET reaction are close to unity (0.88-0.99).