At presence of molecular oxygen, the energy stored at the triplet ensembles of variety of organic molecules, capable of energy transfer via an emissive process (phosphorescence) or a non-emissive process (triplet-triplet transfer) is actively dissipated. The reason for this is the process of singlet oxygen generation. Importantly, singlet oxygen is a highly reactive species, leading to oxidation of the photoactive molecules, followed by further los of efficiency. In this work we demonstrate organic solvents, specially designed and optimized to deliver long-term protection (over 1000 h) against the molecular oxygen quenching, thus comparable efficiencies of the specific process in oxygen-free environment and under ambient conditions are achieved. Sources: “Long-term stable photoactive composition, such as phosphorescent composition or TTA-photon upconversion composition European patent application: Nr. 13 185 751.8 / 2013