Photochemistry of α-Cycloalkoxyacetophenones. Type II and Vibronic Pathways for Radiationless Triplet Decay

Thomas R. Darling, Nicholas J. Turro, Richard H. Hirsch, Frederick D. Lewis

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Medium and small ring α-cycloalkoxyacetophenones other than α-cyclopropoxyacetophenones undergo normal photochemical type II reactions with high efficiency. The products obtained are a novel family of 1-oxaspiro[3.n]alkanes as well as the corresponding cycloalkanones. The photochemical behavior of α-cyclopropoxyacetophenones deviates markedly from that of their higher homologs and is characterized by: (1) low efficiency of product formation, (2) unprecedented cis-trans isomerization of the cyclopropane ring for the α-(2,3-dimethylcyclopropoxy) acetophenones, and (3) triplet lifetimes which are shortened by remote ring methyl substitution. Replacement of the γ hydrogen with deuterium increases the triplet lifetime and the quantum yields for the type II and ring isomerization processes. Both the ring isomerization and the rapid radiationless decay of the triplet state are attributed to vibronic energy transfer between the excited carbonyl chromophore and the γ hydrogencyclopropyl unit.

Original languageEnglish (US)
Pages (from-to)434-439
Number of pages6
JournalJournal of the American Chemical Society
Volume96
Issue number2
DOIs
StatePublished - Jan 1 1974

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Acetophenones
Photochemistry
Alkanes
Deuterium
Photochemical reactions
Energy Transfer
Isomerization
Hydrogen
Quantum yield
Chromophores
Energy transfer
Paraffins
Substitution reactions
cyclopropane

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

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title = "Photochemistry of α-Cycloalkoxyacetophenones. Type II and Vibronic Pathways for Radiationless Triplet Decay",
abstract = "Medium and small ring α-cycloalkoxyacetophenones other than α-cyclopropoxyacetophenones undergo normal photochemical type II reactions with high efficiency. The products obtained are a novel family of 1-oxaspiro[3.n]alkanes as well as the corresponding cycloalkanones. The photochemical behavior of α-cyclopropoxyacetophenones deviates markedly from that of their higher homologs and is characterized by: (1) low efficiency of product formation, (2) unprecedented cis-trans isomerization of the cyclopropane ring for the α-(2,3-dimethylcyclopropoxy) acetophenones, and (3) triplet lifetimes which are shortened by remote ring methyl substitution. Replacement of the γ hydrogen with deuterium increases the triplet lifetime and the quantum yields for the type II and ring isomerization processes. Both the ring isomerization and the rapid radiationless decay of the triplet state are attributed to vibronic energy transfer between the excited carbonyl chromophore and the γ hydrogencyclopropyl unit.",
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Photochemistry of α-Cycloalkoxyacetophenones. Type II and Vibronic Pathways for Radiationless Triplet Decay. / Darling, Thomas R.; Turro, Nicholas J.; Hirsch, Richard H.; Lewis, Frederick D.

In: Journal of the American Chemical Society, Vol. 96, No. 2, 01.01.1974, p. 434-439.

Research output: Contribution to journalArticle

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N2 - Medium and small ring α-cycloalkoxyacetophenones other than α-cyclopropoxyacetophenones undergo normal photochemical type II reactions with high efficiency. The products obtained are a novel family of 1-oxaspiro[3.n]alkanes as well as the corresponding cycloalkanones. The photochemical behavior of α-cyclopropoxyacetophenones deviates markedly from that of their higher homologs and is characterized by: (1) low efficiency of product formation, (2) unprecedented cis-trans isomerization of the cyclopropane ring for the α-(2,3-dimethylcyclopropoxy) acetophenones, and (3) triplet lifetimes which are shortened by remote ring methyl substitution. Replacement of the γ hydrogen with deuterium increases the triplet lifetime and the quantum yields for the type II and ring isomerization processes. Both the ring isomerization and the rapid radiationless decay of the triplet state are attributed to vibronic energy transfer between the excited carbonyl chromophore and the γ hydrogencyclopropyl unit.

AB - Medium and small ring α-cycloalkoxyacetophenones other than α-cyclopropoxyacetophenones undergo normal photochemical type II reactions with high efficiency. The products obtained are a novel family of 1-oxaspiro[3.n]alkanes as well as the corresponding cycloalkanones. The photochemical behavior of α-cyclopropoxyacetophenones deviates markedly from that of their higher homologs and is characterized by: (1) low efficiency of product formation, (2) unprecedented cis-trans isomerization of the cyclopropane ring for the α-(2,3-dimethylcyclopropoxy) acetophenones, and (3) triplet lifetimes which are shortened by remote ring methyl substitution. Replacement of the γ hydrogen with deuterium increases the triplet lifetime and the quantum yields for the type II and ring isomerization processes. Both the ring isomerization and the rapid radiationless decay of the triplet state are attributed to vibronic energy transfer between the excited carbonyl chromophore and the γ hydrogencyclopropyl unit.

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