Osmium metal complexes are of interest as they exhibit visible luminescence upon excitation with visible or ultraviolet light and as such are possible models of photosynthetic reaction center, possible energy and electron transfer agents, and possible photochemical or electrochemical reaction catalysts. Recently we have synthesized a series bis-(diimine)carbonyltriphenylphosphine osmium (II) complexes using eight substituted diimines and nine substituted triphenylphosphines. We will discuss the characterization of the electronic states of these compounds by cyclic voltammetry, UV-visible absorbance and emission spectroscopies as well as time resolved emission lifetime studies. We will discuss our conclusions about the effect of this ligand variation on the electronic properties of these compounds.