Radiationless Deactivation of the Second Excited Singlet State 1Σg+ of O2 in Solution

The deactivation of the upper excited singlet oxygen O 2 ( 1 Σ g + ) by 22 different quenchers has been studied in the liquid phase by time-resolved emission experiments. Radiationless deactivation occurs by electronic to vibrational (e−v) energy transfer to terminal bonds X−Y of the quenching molecule. A model is presented which describes the broad variation of rate constants over 4 orders of magnitude. The quantitative comparison with the e−v deactivation of O 2 ( 1 Δ g ) demonstrates that for O 2 ( 1 Σ g + ) in addition to the excitation of stretching modes the excitation of bending modes of X−Y becomes important for the overall deactivation process.