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Time-Resolved Insight into the Photosensitized Generation of Singlet Oxygen in Endoperoxides.

Martínez-Fernández L, González-Vázquez J, González L, Corral I - J Chem Theory Comput (2014)

Bottom Line: Electronic excitation of endoperoxides triggers two competing pathways, cycloreversion and O-O homolysis, that result in the generation of singlet oxygen and oxygen diradical rearrangement products.The triplet states do not intervene in this mechanism, as opposed to the O-O homolysis where the exchange of population between the singlet and triplet manifolds is remarkable.In line with recent experiments performed on the larger anthracene-9,10-endoperoxide, upon excitation to the spectroscopic ππ* electronic states, the primary photoreactive pathway that governs deactivation of endoperoxides is O-O homolysis with a quantum yield of 65%.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Química, Universidad Autónoma de Madrid , 28049 Cantoblanco, Madrid, Spain.

ABSTRACT

A synergistic approach combining high-level multiconfigurational static calculations and full-dimensional ab initio surface hopping dynamics has been employed to gain insight into the photochemistry of endoperoxides. Electronic excitation of endoperoxides triggers two competing pathways, cycloreversion and O-O homolysis, that result in the generation of singlet oxygen and oxygen diradical rearrangement products. Our results reveal that cycloreversion or the rupture of the two C-O bonds occurs via an asynchronous mechanism that can lead to the population of a ground-state intermediate showing a single C-O bond. Furthermore, singlet oxygen is directly generated in its most stable excited electronic state (1)Δg. The triplet states do not intervene in this mechanism, as opposed to the O-O homolysis where the exchange of population between the singlet and triplet manifolds is remarkable. In line with recent experiments performed on the larger anthracene-9,10-endoperoxide, upon excitation to the spectroscopic ππ* electronic states, the primary photoreactive pathway that governs deactivation of endoperoxides is O-O homolysis with a quantum yield of 65%.

No MeSH data available.


Related in: MedlinePlus

(A) Time evolution ofa representative trajectory leading to BQ+ H2 products. Singlet states are represented as solidlines, (S0 in red, S1 in green, S2 in blue, and S3 in pink), while triplet states are denotedwith dotted lines in light blue T1, yellow T2, black T3, and gray T4. Black points indicatethe current potential energy of the system at each time. The verticaldotted line in black in panel A indicates the point when the trajectoryreaches the S0 and the energy scaling is switched off.(B) Snapshots for longer propagation times and the optimized geometryof the TSH2 for comparison. Note that for thistrajectory deuterium atoms where replaced by hydrogens (see text).
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fig7: (A) Time evolution ofa representative trajectory leading to BQ+ H2 products. Singlet states are represented as solidlines, (S0 in red, S1 in green, S2 in blue, and S3 in pink), while triplet states are denotedwith dotted lines in light blue T1, yellow T2, black T3, and gray T4. Black points indicatethe current potential energy of the system at each time. The verticaldotted line in black in panel A indicates the point when the trajectoryreaches the S0 and the energy scaling is switched off.(B) Snapshots for longer propagation times and the optimized geometryof the TSH2 for comparison. Note that for thistrajectory deuterium atoms where replaced by hydrogens (see text).

Mentions: In this section,several trajectories representative for the O–O homolysis andcycloreversion photoreactions will be discussed in detail. Figures 6 and 7A, respectively, exemplifythe generation of 1O2 and H2 fromexcited CHDEPO.


Time-Resolved Insight into the Photosensitized Generation of Singlet Oxygen in Endoperoxides.

Martínez-Fernández L, González-Vázquez J, González L, Corral I - J Chem Theory Comput (2014)

(A) Time evolution ofa representative trajectory leading to BQ+ H2 products. Singlet states are represented as solidlines, (S0 in red, S1 in green, S2 in blue, and S3 in pink), while triplet states are denotedwith dotted lines in light blue T1, yellow T2, black T3, and gray T4. Black points indicatethe current potential energy of the system at each time. The verticaldotted line in black in panel A indicates the point when the trajectoryreaches the S0 and the energy scaling is switched off.(B) Snapshots for longer propagation times and the optimized geometryof the TSH2 for comparison. Note that for thistrajectory deuterium atoms where replaced by hydrogens (see text).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4325559&req=5

fig7: (A) Time evolution ofa representative trajectory leading to BQ+ H2 products. Singlet states are represented as solidlines, (S0 in red, S1 in green, S2 in blue, and S3 in pink), while triplet states are denotedwith dotted lines in light blue T1, yellow T2, black T3, and gray T4. Black points indicatethe current potential energy of the system at each time. The verticaldotted line in black in panel A indicates the point when the trajectoryreaches the S0 and the energy scaling is switched off.(B) Snapshots for longer propagation times and the optimized geometryof the TSH2 for comparison. Note that for thistrajectory deuterium atoms where replaced by hydrogens (see text).
Mentions: In this section,several trajectories representative for the O–O homolysis andcycloreversion photoreactions will be discussed in detail. Figures 6 and 7A, respectively, exemplifythe generation of 1O2 and H2 fromexcited CHDEPO.

Bottom Line: Electronic excitation of endoperoxides triggers two competing pathways, cycloreversion and O-O homolysis, that result in the generation of singlet oxygen and oxygen diradical rearrangement products.The triplet states do not intervene in this mechanism, as opposed to the O-O homolysis where the exchange of population between the singlet and triplet manifolds is remarkable.In line with recent experiments performed on the larger anthracene-9,10-endoperoxide, upon excitation to the spectroscopic ππ* electronic states, the primary photoreactive pathway that governs deactivation of endoperoxides is O-O homolysis with a quantum yield of 65%.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Química, Universidad Autónoma de Madrid , 28049 Cantoblanco, Madrid, Spain.

ABSTRACT

A synergistic approach combining high-level multiconfigurational static calculations and full-dimensional ab initio surface hopping dynamics has been employed to gain insight into the photochemistry of endoperoxides. Electronic excitation of endoperoxides triggers two competing pathways, cycloreversion and O-O homolysis, that result in the generation of singlet oxygen and oxygen diradical rearrangement products. Our results reveal that cycloreversion or the rupture of the two C-O bonds occurs via an asynchronous mechanism that can lead to the population of a ground-state intermediate showing a single C-O bond. Furthermore, singlet oxygen is directly generated in its most stable excited electronic state (1)Δg. The triplet states do not intervene in this mechanism, as opposed to the O-O homolysis where the exchange of population between the singlet and triplet manifolds is remarkable. In line with recent experiments performed on the larger anthracene-9,10-endoperoxide, upon excitation to the spectroscopic ππ* electronic states, the primary photoreactive pathway that governs deactivation of endoperoxides is O-O homolysis with a quantum yield of 65%.

No MeSH data available.


Related in: MedlinePlus