The energy migration dynamics have been studied in multi-centered assemblies embedded in poly(methyl methacrylate) (PMMA) films using steady-state and time-resolved emission techniques. The assemblies consist of twenty Ru(II) and Os(II) polypyridyl coordination complexes linked through a polystyrene backbone. Energy migration is initiated by photoexcitation of one of the Ru(II) sites and terminated upon sensitization of a low-energy Os trap. The inhomogeneous environment of the assembly results in a distribution of excited-state energies, which is frozen in time due to the rigidity of the PMMA film. Energy migration proceeds toward the lower energy sites, resulting in a time-dependent red-shift in the polymer emission band.