Energy Transfer between Singlet (¹Δ_g) and Triplet (³Σ_g^-) Molecular Oxygen in Aqueous Solution

We clearly demonstrate the occurrence of energy transfer between ¹⁸O₂ (¹Δ_g) and ¹⁶O₂ in the ground state (³Σ_g^-) with subsequent conversion of the latter species into its singlet excited state (¹Δ_g) in aqueous solution. This was inferred from the results of incubation experiments involving DHPN¹⁸O₂ as a chemical generator of ¹⁸O₂ (¹Δ_g) and the water-soluble disodium salt of anthracene (EAS) used as a chemical trap of singlet oxygen. The products of the reaction were accurately analyzed by HPLC-ESI-MS.