The binuclear complex Ru-II(Me(2)phen)(2)-(Mebpy-CH2-CH2-Mebpy)-Rh-III(Me(2)pby)(2)(5+) (Me(2)phen = 4,7-dimethyl-1,10- phenanthroline; Mebpy = 4-methyl-2,2’-bipyridine; Me(2)bpy = 4,4’-dimethyl-2,2’-bipyridine), hereafter represented by Ru(II)-Rh(III), was synthesized and studied. Selective excitation of the two moieties of the dyad was achieved with visible (100% *Ru(II)-Rh(III)) or ultraviolet light (e.g., at 298 nm, 70% Ru(II)-*Rh(III)), In room-temperature fluid solutions, both local excited states are quenched by electron transfer, leading to a common Ru(III)-Rh(II) state. The two forward electron-transfer processes, as well as the recombination process leading back to the ground state, can be resolved by transient laser spectroscopy, using various excitation wavelengths and pulse widths (532 nm, 30 ps; 427 nm, 0.5 ps; 298 nm, 0.5 ps). Rate constants in acetonitrile are as follows : *Ru(II)-Rh(III) --> Ru(III)-Rh(II), 1.7 X 10(8) s(-1); Ru(II)-*Rh(III) --> Ru(III)-Rh(II), 3.3 x 10(10) s(-1); Ru(III)-Rh(II) --> Ru(II)-Rh(III), 7.1 x 10(9) s(-1). The rate constants can be rationalized in terms of standard electron-transfer theory, assuming that the driving force (Delta G degrees =-0.10, -0.70, and -2.07 eV, respectively) is the main variable parameter. The two forward processes belong to the "normal", and the back reaction belongs to the "inverted" free-energy regime. In room-temperature fluid solution, no Ru(II)-*Rh(III) --> *Ru(II)-Rh(III) energy transfer (Delta G degrees =-0.61 eV) is observed, presumably because of efficient competition by the faster Ru(II)-*Rh(III) --> Ru(III)-Rh(II) electron-transfer quenching. By contrast, this process becomes efficient in rigid media (room-temperature or 77 K), where both the *Ru(II)-Rh(III) --> Ru(III)-Rh(II) and Ru(II)-*Rh(III) --> Ru(III)-Rh(II) electron-transfer processes are blocked as a consequence of restricted solvent repolarization. In 77 K ethanol glass, the energy-transfer rate constant is 1.9 X 10(6) s(-1).