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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

Time evolutionof the average quantum probability of singlet (S0 in red,S1 in green, S2 dark blue,S3 in pink) and triplet (T1 in light blue, T2 in yellow, T3 in black, T4 in gray)states.
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fig4: Time evolutionof the average quantum probability of singlet (S0 in red,S1 in green, S2 dark blue,S3 in pink) and triplet (T1 in light blue, T2 in yellow, T3 in black, T4 in gray)states.

Mentions: Figure 4 shows the timeevolution of the four singlet (S0, S1, S2, and S3) and fourtriplet states (T1, T2, T3, and T4) population of the 78 trajectories propagated, created usingdeuterated CHDEPO, along 100 fs. Although the propagation was donein 16 spin–orbit states, arising from the diagonalization ofthe total Hamiltonian, for simplicity the analysis will be done onthe spin-free states, where the electronic wave function was projectedback into the initial singlet and triplet states. Initially, the trajectoriesare distributed according to a 65:35 ratio between the S2 and S3 electronic states. This translates into a mixtureof π*OOσ*OO and π*OOπ*CC states, where the π*OOπ*CC states are dominant (85% vs 15%).


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)

Time evolutionof the average quantum probability of singlet (S0 in red,S1 in green, S2 dark blue,S3 in pink) and triplet (T1 in light blue, T2 in yellow, T3 in black, T4 in gray)states.
© Copyright Policy
Related In: Results  -  Collection

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

fig4: Time evolutionof the average quantum probability of singlet (S0 in red,S1 in green, S2 dark blue,S3 in pink) and triplet (T1 in light blue, T2 in yellow, T3 in black, T4 in gray)states.
Mentions: Figure 4 shows the timeevolution of the four singlet (S0, S1, S2, and S3) and fourtriplet states (T1, T2, T3, and T4) population of the 78 trajectories propagated, created usingdeuterated CHDEPO, along 100 fs. Although the propagation was donein 16 spin–orbit states, arising from the diagonalization ofthe total Hamiltonian, for simplicity the analysis will be done onthe spin-free states, where the electronic wave function was projectedback into the initial singlet and triplet states. Initially, the trajectoriesare distributed according to a 65:35 ratio between the S2 and S3 electronic states. This translates into a mixtureof π*OOσ*OO and π*OOπ*CC states, where the π*OOπ*CC states are dominant (85% vs 15%).

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