Photophysical properties ofRu(bpy)$+ , Ru(bpy),(biq)*+, and Os(bpy):+ (bpy=2,2'-bipyridine; biq=2,2'-biquinoline) in poly (ethyleneoxide) matrices (PEO) constituted by (-CHz-CHz-0-) repeating units, with averagemolecular weight 400 (PEO-400, a highly viscous fluid) and 600000 dalton (PEO-600000, a semicrystalline solid) have been studied at room temperature and 77 K. Comparison with similar systems is made. The absorption spectra, luminescence spectra and lifetimes at room temperature of the three complexes in both matrices are in agreement with the typical features reported for the same complexes in fluid solutions, and indicate that fast excited state relaxation via solvent reorganization occurs in both PEO matrices at room temperature. Such behaviout is not usual for solid matrices and is attributed to the microheterogeneous nature of PEO-600000 and to the ability of the solid PEO amorphous region to stabilize polar species within the timescale of radiative relaxation. The results suggest that PEO-600000 is a promising medium for studying electron and energy transfer processes having mild driving forces in the solid state at room temperature.