A study of antenna-initiated photochemistry of polyfunctional steroids and excited state interactions involving carbon-chlorine bonds
Abstract
We have been interested in the use of "antenna" chromophores to "harvest" photon energy which can then be utilized to selectively activate functionalites distal to the site of initial excitation. The first part of this thesis involved the synthesis and photochemistry of polyfunctional steroids. Information had been gathered in earlier work in which photolysis of 3$\alpha$-(dimethyl-phenylsiloxy)-5$ \alpha$-androstane-11,17-dione (5) in the presence of triethylamine with 266-nm laser light led to triplet derived reduction at C17. It was proposed that the C11 carbonyl was serving as a "singlet-triplet switch". Compounds 1-4 were studied in order to test the singlet-triplet switch concept. Compounds 2-4 have been photolyzed with light (266 nm) absorbed by the DPSO "antenna". Z-E isomerization of the olefin is observed in all three cases, with quantum efficiencies comparable to, or greater than, the model compound 1, lacking the ketone group. The second part of this thesis involved the photochemistry and photophysics of exo-6-chloro-1-trimethylsilyl-2-(trimethylsiloxy)norbornene (1-TMS-ExoCl). NBO calculations predicted enhanced orbital mixing. The predicted perturbation was verified by the bathochromic shift in the absorption spectrum of 1-TMS-ExoCl relative to the model compound, ExoCl. However, the quantum efficiency of photodehalogenation of 1-TMS-ExoCl was calculated to be 0.022 compared with 0.066 for the ExoCl. In addition, the predicted photodehalogenation product was not observed but instead, two new photoproducts were produced.
Degree
Ph.D.
Advisors
Morrison, Purdue University.
Subject Area
Organic chemistry|Biochemistry
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