We report results from experiments with the quinoline-O2 complex, which was photodissociated using light near 312 nm. Photodissociation resulted in formation of the lowest excited state of oxygen, O2 a 1Δg, which we detected using resonance enhanced multiphoton ionization and velocity map ion imaging. The O2+ ion image allowed for a determination of the center-of-mass translational energy distribution, P(ET), following complex dissociation. We also report results of electronic structure calculations for the quinoline singlet ground state and lowest energy triplet state. From the CCSD/aug-cc-pVDZ//(U)MP2/cc-pVDZ calculations, we determined the lowest energy triplet state to have ππ* electronic character and to be 2.69 eV above the ground state. We also used electronic structure calculations to determine the geometry and binding energy for several quinoline-O2 complexes. The calculations indicated that the most strongly bound complex has a well depth of about 0.11 eV and places the O2 moiety above and approximately parallel to the quinoline ring system. By comparing the experimental P(ET) with the energy for the singlet ground state and the lowest energy triplet state, we concluded that the quinoline product was formed in the lowest energy triplet state. Finally, we found the experimental P(ET) to be in agreement with a Prior translational energy distribution, which suggests a statistical dissociation for the complex.
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This content will become publicly available on June 17, 2025
A computational study of possible mechanisms of singlet oxygen generation in miniSOG photoactive protein
We report high-level electronic structure calculations of electronic states in the miniSOG (for mini Singlet Oxygen Generator) photoactive protein designed to produce singlet oxygen upon light exposure. We consider a model system with a riboflavin (RF) chromophore. To better understand the photosensitization process, we compute relevant electronic states of the combined oxygen-chromophore system and their couplings. The calculations suggest that singlet oxygen can be produced both by inter-system crossing, via a triplet state of the RF(T1)×O2(3Σ− g ) character as well as by triplet excitation energy transfer via a singlet state of the same character. Importantly, the former channel produces O2(1Σ+ g ), an excited state of singlet oxygen, which is known to convert with unit efficiency into O2(1∆g) The calculations also provide evidence for the production of the triplet state of the chromophore via internal conversion facilitated by oxygen. Our results provide concrete support to previously hypothesized scenarios.
more » « less- Award ID(s):
- 2154482
- NSF-PAR ID:
- 10522693
- Publisher / Repository:
- Mol.Phys
- Date Published:
- Format(s):
- Medium: X
- Institution:
- University of Southern California
- Sponsoring Org:
- National Science Foundation
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Abstract The chemical stability and the low‐lying singlet and triplet excited states of BN‐
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