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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

Globalstatic picture of the O–O homolysis mechanism ofCHDEPO based on MEP calculations (from this work and ref (21e)). Final energies relativeto the GS minimum (in eV) were calculated at MS-CASPT2//SA4-CASSCF(14,12)/ANO-RCClevel of theory. Bond distances in angstroms. The state labeling wasinferred from the final products of the MEP. The label 4CI standsfor a degeneracy of four singlet states.
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fig2: Globalstatic picture of the O–O homolysis mechanism ofCHDEPO based on MEP calculations (from this work and ref (21e)). Final energies relativeto the GS minimum (in eV) were calculated at MS-CASPT2//SA4-CASSCF(14,12)/ANO-RCClevel of theory. Bond distances in angstroms. The state labeling wasinferred from the final products of the MEP. The label 4CI standsfor a degeneracy of four singlet states.

Mentions: Figure 2 showsthe scheme proposed for O–Ohomolysis mechanism based on the CASSCF MEP calculated following thegradient of the second root (i.e., first excited state). Similarlyto previous calculations for the same21e and other endoperoxides,21c the MEP fromthe Franck–Condon region leads barrierlessly to an energeticallyaccessible high degeneracy point of four singlet states (4CI), amongwhich the GS is included. Structurally speaking, this correspondsto a point of the PES where the system presents an internuclear O–Odistance at which the distribution of six electrons into the πOO, π*OO, σOO and σ*OO orbitals leads to four different configurations energeticallyindistinguishable.


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)

Globalstatic picture of the O–O homolysis mechanism ofCHDEPO based on MEP calculations (from this work and ref (21e)). Final energies relativeto the GS minimum (in eV) were calculated at MS-CASPT2//SA4-CASSCF(14,12)/ANO-RCClevel of theory. Bond distances in angstroms. The state labeling wasinferred from the final products of the MEP. The label 4CI standsfor a degeneracy of four singlet states.
© Copyright Policy
Related In: Results  -  Collection

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

fig2: Globalstatic picture of the O–O homolysis mechanism ofCHDEPO based on MEP calculations (from this work and ref (21e)). Final energies relativeto the GS minimum (in eV) were calculated at MS-CASPT2//SA4-CASSCF(14,12)/ANO-RCClevel of theory. Bond distances in angstroms. The state labeling wasinferred from the final products of the MEP. The label 4CI standsfor a degeneracy of four singlet states.
Mentions: Figure 2 showsthe scheme proposed for O–Ohomolysis mechanism based on the CASSCF MEP calculated following thegradient of the second root (i.e., first excited state). Similarlyto previous calculations for the same21e and other endoperoxides,21c the MEP fromthe Franck–Condon region leads barrierlessly to an energeticallyaccessible high degeneracy point of four singlet states (4CI), amongwhich the GS is included. Structurally speaking, this correspondsto a point of the PES where the system presents an internuclear O–Odistance at which the distribution of six electrons into the πOO, π*OO, σOO and σ*OO orbitals leads to four different configurations energeticallyindistinguishable.

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