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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.
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Stimulated Raman Generation of Aqueous Singlet Oxygen without Photosensitizers
Singlet oxygen is traditionally produced via photosensitizer molecules such as methylene blue, which function as catalysts. Here we investigate stimulated Raman generation of singlet oxygen from dissolved oxygen in both water (H2O) and heavy water (D2O) using nanosecond-pulsed visible blue laser light in the 400–440 nm spectral region without singlet oxygen photosensitizers. We report an oxygen-dependent Stokes peak in the red spectrum (600–670 nm) that is identical when produced in H2O and D2O. These red Stokes photons are not detected when an oxygen quencher is present. Temporal photodepletion of the uric acid absorbance peak at 294 nm is consistent with singlet oxygen generation. We postulate that a two-photon stimulated Raman process produces singlet oxygen from O2 dissolved within the solvents. We note that the energy difference between input and output photons of 0.97 eV is precisely the energy needed to excite O2 to its singlet state
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- Award ID(s):
- 1831332
- PAR ID:
- 10355677
- Date Published:
- Journal Name:
- Journal of photochemistry and photobiology
- Volume:
- 235
- ISSN:
- 1011-1344
- Page Range / eLocation ID:
- 112562
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/https://doi.org/10.1016/j.jphotobiol.2022.112562
