University of Illinois Urbana-Champaign

The Chemistry of Aroyl Azides in Piperidine- and Steroid-Separated Bichromophoric System: Photoinduced Long-Distance Intramolecular Electron Transfer Reactions

Zhu, Yong

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Description

Title
The Chemistry of Aroyl Azides in Piperidine- and Steroid-Separated Bichromophoric System: Photoinduced Long-Distance Intramolecular Electron Transfer Reactions
Author(s)
Zhu, Yong
Issue Date
1992
Doctoral Committee Chair(s)
Schuster, Gary B.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
  • Chemistry, Inorganic
  • Chemistry, Organic
  • Chemistry, Physical
Abstract
The photochemistry and photophysics of piperidine- and steroid- separated bichromophoric systems containing an aroyl azide as the electron acceptor and secondary aromatic amines as the electron donors was examined. We report the first example of unique photochemical reactivity associated with through-bond electron transfer in these bichromophores. Light absorbed by the aroyl azide acceptor chromophore of these compounds gives isocyanate by the photo-Curtius rearrangement and nitrene by loss of nitrogen. Light absorbed by the aryl amine donor chromophores initiates a through-bond electron-transfer reaction to form high energy, charge-separated intermediate states. The aryl amine radical cations were detected by pulsed laser spectroscopy and the highly reactive aroyl azide radical anions were identified by the results of steady-state photolysis. In acetonitrile and in methyl alcohol solution, the photoexcited aryl amine converts the azide to a primary amide. The mechanism of this reaction is thought to involve long-range electron transfer to form first the azide and then nitrene radical anion intermediates. Similar irradiation of the bichromophoric system in cyclohexane solution converts the azide to a secondary amide. In this case the reaction seems to proceed through a nitrene intermediate. The photolysis efficiency of the azide is solvent-independent, and is not affected significantly by the orientation of amine group (the cis or trans). Intramolecular electron-transfer from the singlet and triplet excited state of the donor chromophore plays an important role and triplet-triplet energy transfer mechanism may also be involved in this chemistry. The mechanism for the reaction is supported by fluorescence quenching and laser flash photolysis experiments and by quenching and trapping studies.
Graduation Semester
1992
Type of Resource
text
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http://hdl.handle.net/2142/72275

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