O2 quenching of ruthenium(II) tris(2,2′-bypyridyl)2+ within the water pool of perfluoropolyether-based reverse micelles formed in supercritical carbon dioxide

We report on the effects of O-2 on the luminescence quenching of ruthenium(II) tris(2,2'-bipyridyl) cation, [Ru(bpy)3(2+)], sequestered within the water pool region of perfluoropolyether (PFPE)-based reverse micelles formed in supercritical carbon dioxide (scCO(2)). A Stern-Volmer quenching model cannot describe the O-2-dependent [Ru(bpy)(3)(2+)] quenching profiles in the PFPE micelles. A "two-site" model is needed to describe the observed quenching. The mean quenching efficiency is similar to 50-fold higher when the molar ratio of water to PFPE (omega(o)) is less than or equal to 10 as compared to omega(o) = 20. At omega(o) values of 10 or less, 95+% of the [Ru(bpy)(3)(2+)] molecules within the water pool are located in close proximity to the carboxylate headgroups within the micelle water pool and they are quenched very effectively by the O-2 dissolved within the scCO(2). At the highest omega(o) values studied, 60-65% of the [Ru(bpy)(3)(2+)] within the water pool remains near the carboxylate headgroups; a substantial fraction (35-40%) Df the [Ru(bpy)(3)(2+)] is distributed more toward the center of water pool away from anionic surfactant headgroups. Those [Ru(bpy)(3)(2+)] luminophores that are away from the headgroups (more toward the water pool center) are not quenched as effectively by O-2 because the O-2 solubility in water is significantly lower compared to scCO(2).