Confirming the stimulated Raman origin of singlet‐oxygen photogeneration

Abstract

We confirm the Raman origin of the singlet oxygen photogenerated in water environments without using photosensitizers. Nanosecond light pulses in the blue region of the spectra (405–480 nm) generate Raman Stokes excitation of singlet oxygen in the red region (600–670 nm) when focusing on pure distilled water. The excitation also produces Stokes components corresponding to the stretching modes of water molecules. The time evolution of both types of Stokes components, singlet oxygen, and stretching modes correspond to the time duration of the excitation pulse as expected for a Raman process. Their power dependences are also similar. Finally, both signals exhibit high refractive ring structures due to the nonlinear optical interaction generated by the stimulated Raman process.

Singlet Oxygen Photophysics: From Liquid Solvents to Mammalian Cells

“…As an addendum to this discussion, we note that O 2 (a 1 Δ g ) has also been produced via a Raman process in liquid H 2 O and D 2 O where the energy difference between the incoming UV pump photons and the outgoing visible Stokes photons corresponds to the O 2 (a 1 Δ g ) excitation energy. 761,762 Although the authors of this study were not able to quantify the amount of O 2 (a 1 Δ g ) produced by detecting the characteristic 1275 nm O 2 (a 1 Δ g ) → O 2 (X 3 Σ g − ) phosphorescence, they provided other evidence to substantiate O 2 (a 1 Δ g ) production (e.g., effects of added quenchers).…”