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

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Zhu, Yong

Contributors dc:contributor

• Schuster, Gary B.

• Chemistry, Inorganic
• Chemistry, Organic
• Chemistry, Physical

Identifier

(UMI)AAI9305750

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/72275