A DFT-based computational study performed in the gas phase and in acetonitrile on polypyridine ruthenium isomer complexes [Ru(tpy)(bpy)(POPh)](2+) and [Ru(tpy)(bpy)(OPPh)](2+) (bpy = 2,2'-bipyridine, tpy = 2,2':6',2″-terpyridine, Ph = phenyl) predicts that they constitute a prototype for a new family of inorganic photochromic systems. The two isomers are found to absorb in different spectral regions to excited states that are connected adiabatically through a thermodynamically and kinetically favorable triplet potential energy profile. Nonadiabatic routes were identified and shown to be preferable over the adiabatic mechanism. The reverse isomerization reaction is found to be achievable only thermally. The current predictive work will be of prime importance to experimentalists for the design of new inorganic phosphorus-based compounds with attractive photochromic properties.