Homo- and heterobimetallic complexes of compositions [(bpy)(2)Ru-II(phen-Hbzim-tpy)Ru-II(tpy/tpy-PhCH3/H(2)pbbzim)](4+) and [(bpy)(2)Ru-II(phen-Hbzim-tpy)-Rh-III(tpy-PhCH3/H(2)pbbzim)](5+), where phen-Hbzim-tpy = 2-[4-(2,6-dipyridin-2-ylpyridin-4-yl)phenyl]-1H-imidazole[4,5-f][1,10]phenanthroline, bpy = 2,2'-bipyridine, tpy = 2,2':6',2 ''-terpyridine, tpy-PhCH3 = 4'-(4-methylphenyl)-2,2':6',2 ''-terpyridine, and H(2)pbbzim = 2,6-bis(benzimidazol-2-yl)-pyridine, have been synthesized and characterized by elemental analyses, electrospray ionization mass spectrometry, and H-1 NMR spectroscopy. The absorption spectra, redox behavior, and luminescence properties of these bimetallic complexes have been thoroughly investigated and compared with those of monometallic [(bpy)(2)Ru-II(phen-Hbzim-tpy)](2+) and [(tpy-PhCH3)Rh-III (tpy-Hbzim-phen)](3+) model compounds. The electro-chemistry of the complexes shows a reversible Ru-II/III oxidation in the anodic region and an irreversible Rh-III/I reduction and several ligand-based reductions in the cathodic region. Steady-state and time-resolved luminescence data at room temperature show that an efficient intramolecular electronic energy transfer from the metal-to-ligand charge-transfer (MLCT) excited state of the [(byy)(2)Ru-II(phen-Hbzim-tpy)] chromophore to the MLCT state of the tpy-containing chromophore [(phen-Hbzim-tpy)Re-II(tpy/tpy-PhCH3/H(2)pbbzim)] occurs in all three unsymmetrical homobimetallic complexes. On the other hand, for both heterometallic dyads, an efficient intramolecular photoinduced electron transfer from the excited ruthenium moiety to the rhodium-based unit takes place. The rate constants for the energy- and electron-transfer processes have been determined by time-resolved emission spectroscopy. The influence of the pH on the absorption, steady-state, and time-resolved emission properties of complexes has been thoroughly investigated. The absorption titration data were used to determine the ground-state pK values, whereas the luminescence data were utilized for determination of the excited-state acid dissociation constants. In effect, deprotonation of the azole NH moieties of the complexes leads to a substantial lowering of the MLCT absorption and emission band energies.