The synthesis, electrochemistry, and photophysical characterization are reported for 11 tris(bidentate) cyclometalated ruthenium(II) compounds, [Ru(N boolean AND N)(2)(C boolean AND N)(+). The electro-chemical and photophysical properties were varied by the addition of substituents on the 2,2'-bipyridine, N boolean AND N, and 2-phenylpyridine, C boolean AND N, ligands with different electron-donating and -withdrawing groups. The systematic tuning of these properties offered a tremendous opportunity to investigate the origin of the rapid excited-state decay for these cyclometalated compounds and to probe the accessibility of the dissociative, ligand-field (LF) states from the metal-to-ligand charge-transfer (MLCT) excited state. The photoluminescence quantum yield for [Ru(N boolean AND N)(2)(C boolean AND N)](+) increased from 0.0001 to 0.002 as more electron-withdrawing substituents were added to C boolean AND N. An analogous substituent dependence was observed for the excited state lifetimes, tau(obs), which ranged from 3 to 40 ns in neat acetonitrile, significantly shorter than those for their [Ru(N boolean AND N)(3)](2+) analogues. The excited-state decay for [Ru(N boolean AND N),(C boolean AND N)(+) was accelerated because of an increased vibronic overlap between the ground- and excited-state wavefunctions rather than an increased electronic coupling as revealed by a comparison of the Franck Condon factors. The radiative (k(r)) and non-radiative (k(nr)) rate constants of excited-state decay were determined to be on the order of 10(4) and 10(7)-10(8) s(-4), respectively. For sets of [Ru(N boolean AND N)(2)(C boolean AND N)](+) compounds functionalized with the same N boolean AND N ligand, knr scaled with excited-state energy in accordance with the energy gap law. Furthermore, an Arrhenius analysis of robs for all of the compounds between 273 and 343 K was consistent with activated crossing into a single, fourth (MLCT)-M-3 state under the conditions studied with preexponential factors on the order of 10(8)-10(9) s(-4) and activation energies between 300 and 1000 cm(-1). This result provides compelling evidence that LF states are not significantly populated near room temperature unlike many ruthenium(II) polypyridyl compounds. On the basis of the underlying photophysics presented here for [Ru(N boolean AND N)(2)(C boolean AND N)](+), molecules of this type represent a robust class of compounds with built-in design features that should greatly enhance the molecular photostability necessary for photochemical and photoelectrochemical applications.