Reversible Exciplex Formation between Singlet Oxygen, 1Δg, and Vitamin E. Solvent and Temperature Effects

A. A. Gorman; I. R. Gould; I. Hamblett; M. C. Standen

doi:10.1021/ja00335a014

Reversible Exciplex Formation between Singlet Oxygen, ¹Δ_g, and Vitamin E. Solvent and Temperature Effects

A. A. Gorman, I. R. Gould, I. Hamblett, M. C. Standen

Research output: Contribution to journal › Article › peer-review

91 Scopus citations

Abstract

Pulsed nitrogen laser excitation has been used to determine rate and activation parameters for the reaction of singlet oxygen with α-tocopherol (α-T; vitamin E), 6-hydroxy-2,2,5,7,8-pentamethylchroman (HPMC), and 2,4,6-tri-tert-butylphenol (TTBP) in five solvents. The experimental activation enthalpies for α-T and HPMC, predominantly physical quenchers, are significantly more negative than values previously determined for chemical quenchers of ¹Δ_g, and it is concluded that these reactions proceed via the intermediacy of an exciplex which is formed reversibly. It is concluded that the balance between physical and chemical quenching is a sensitive function of spin-orbit coupling properties and entropy factors which play a dominant role as a consequence of a flat enthalpy profile along the critical portions of the reaction coordinate.

Original language	English (US)
Pages (from-to)	6956-6959
Number of pages	4
Journal	Journal of the American Chemical Society
Volume	106
Issue number	23
DOIs	https://doi.org/10.1021/ja00335a014
State	Published - Jan 1 1984
Externally published	Yes

ASJC Scopus subject areas

Catalysis
Chemistry(all)
Biochemistry
Colloid and Surface Chemistry

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10.1021/ja00335a014

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title = "Reversible Exciplex Formation between Singlet Oxygen, 1Δg, and Vitamin E. Solvent and Temperature Effects",

abstract = "Pulsed nitrogen laser excitation has been used to determine rate and activation parameters for the reaction of singlet oxygen with α-tocopherol (α-T; vitamin E), 6-hydroxy-2,2,5,7,8-pentamethylchroman (HPMC), and 2,4,6-tri-tert-butylphenol (TTBP) in five solvents. The experimental activation enthalpies for α-T and HPMC, predominantly physical quenchers, are significantly more negative than values previously determined for chemical quenchers of 1Δg, and it is concluded that these reactions proceed via the intermediacy of an exciplex which is formed reversibly. It is concluded that the balance between physical and chemical quenching is a sensitive function of spin-orbit coupling properties and entropy factors which play a dominant role as a consequence of a flat enthalpy profile along the critical portions of the reaction coordinate.",

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T1 - Reversible Exciplex Formation between Singlet Oxygen, 1Δg, and Vitamin E. Solvent and Temperature Effects

AU - Gorman, A. A.

AU - Gould, I. R.

AU - Hamblett, I.

AU - Standen, M. C.

PY - 1984/1/1

Y1 - 1984/1/1

N2 - Pulsed nitrogen laser excitation has been used to determine rate and activation parameters for the reaction of singlet oxygen with α-tocopherol (α-T; vitamin E), 6-hydroxy-2,2,5,7,8-pentamethylchroman (HPMC), and 2,4,6-tri-tert-butylphenol (TTBP) in five solvents. The experimental activation enthalpies for α-T and HPMC, predominantly physical quenchers, are significantly more negative than values previously determined for chemical quenchers of 1Δg, and it is concluded that these reactions proceed via the intermediacy of an exciplex which is formed reversibly. It is concluded that the balance between physical and chemical quenching is a sensitive function of spin-orbit coupling properties and entropy factors which play a dominant role as a consequence of a flat enthalpy profile along the critical portions of the reaction coordinate.

AB - Pulsed nitrogen laser excitation has been used to determine rate and activation parameters for the reaction of singlet oxygen with α-tocopherol (α-T; vitamin E), 6-hydroxy-2,2,5,7,8-pentamethylchroman (HPMC), and 2,4,6-tri-tert-butylphenol (TTBP) in five solvents. The experimental activation enthalpies for α-T and HPMC, predominantly physical quenchers, are significantly more negative than values previously determined for chemical quenchers of 1Δg, and it is concluded that these reactions proceed via the intermediacy of an exciplex which is formed reversibly. It is concluded that the balance between physical and chemical quenching is a sensitive function of spin-orbit coupling properties and entropy factors which play a dominant role as a consequence of a flat enthalpy profile along the critical portions of the reaction coordinate.

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Reversible Exciplex Formation between Singlet Oxygen, ¹Δ_g, and Vitamin E. Solvent and Temperature Effects

Abstract

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