Two classes of useful complexes of cis-Ru(bpY-X)(2)(NCS)(2) and [Ru(bpy)(2)(bpy-X)](2+) have been prepared and their spectroscopic and photoelectrochemical properties investigated. All the complexes ([Ru(bpy)(2)(bpy-X)](2+)) examined display luminescence at room temperature. The energy of the emission maximum is red shifted for both electron-withdrawing and electron-donating substituents compared to that of parent [Ru(bpy)(3)](2+) complex. Furthermore, the complexes bearing electron-acceptor substituents have higher luminescence quantum yield and longer excited-state lifetime than that of the compounds bearing electron-donating ones. Such behaviors demonstrate that the values of rate constants for radiationless decay from the luminescent excited state to the ground state are determined not only by the energy gap but also by the nature of the substituents, which presumably influenced the changes in the equilibrium displacement between the two levels. In addition, the photoelectrochemical results of the cis-Ru(bpy-X)(2)(NCS)(2) clearly show that the nature of the substituents on the bpy ligands does not substantially affect the photon-to-electric energy conversion efficiency.