Exchange interaction of O2 and nitroxide radical encounter pair as studied by time-resolved near IR luminescence spectroscopy of O2(1Δg)

Highlights: • O₂(¹Δ_g) phosphorescence was measured in organic solvents and ionic liquids. • Spectral blue-shift was found in the presence of a nitroxide radical. • The blue-shift of about 50 cm⁻¹ was seen in any solvents. • The blue-shift was attributed to exchange interaction of O₂ and nitroxide radical. Phosphorescence spectral shift of singlet oxygen, O₂(¹Δ_g) was studied in the presence of a nitroxide radical quencher. The O₂-nitroxide complex causes a blue-shifts in both molecular solvents and in ionic liquids. The amount of shift is found to be nearly the same for both solvents, about 50 cm⁻¹. This shift was attributed to quartet-doublet energy separation of O₂(³Σ_g⁻)-nitroxide pair by exchange interaction of O₂ and nitroxide radical.