Quenching of the triplet state by O (which has a triplet ground state) as a result of Dexter energy transfer is well known in solutions of phosphorescent heavy-metal complexes and doped polymers. In recent years, phosphorescence porous materials(such as Metal–organic frameworks and Covalent organic frameworks) have shown promising oxygen sensing capabilities, for their non-linear gas-adsorption in ultra-low partial pressures of oxygen.