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Applications Focused Synthetic Modification on Photoremovable Protecting Groups (PRPG) & Photochemical Analysis on Organic Azides and Isoxazoles

Thenna Hewa, Kosala R. S.
http://orcid.org/0000-0001-7529-4750
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1511858669354976

Abstract Details

2017, PhD, University of Cincinnati, Arts and Sciences: Chemistry.
In this dissertation, we report the photochemical mechanistic investigations on triplet sensitized and unsensitized organic azides and isoxazoles. Photochemical decomposition of the parent compounds generates carbon and nitrogen centered reactive intermediates leading to remarkable applications. Furthermore, reported synthetically modified photoremovable protecting group (PRPG) system shows significantly high quantum yield and broaden the applicability of the benzophenone based PRPGs. Detection of reactive intermediates were done at room temperature and cryogenic temperatures. Required photon energy for the photochemical processes were provided using various UV light sources depending on the experimental procedures. Femto to nano second transient UV /Vis and resonance Raman has been used in aiding the characterization of the intermediates at room temperature. Detection of cryogenic temperature intermediates were done using Electron spin resonance (ESR), FT-IR matrix isolation, fluorescence, phosphorescence and UV/Vis spectroscopy techniques. Gaussian 09 computations have used to predict favorability of reaction pathways and molecular properties. Our investigation reported in this dissertation outlines three different radical types, 1) Triplet 1,4-biradicals a) Generation of irreversible imine biradical by expelling of a N2(g) by an excited state intermediate b) Applicability of irreversible imine biradical intermediate in high quantum yield applications 2) Triplet nitrenes a) Generation Feasibility of triplet aryl nitrene from unsensitized precursor and sensitized precursor at ambient and cryogenic temperatures b) Revelation of factors affecting the lifetime of triplet vinylnitrenes, rigidity and the ring strain approach 3) Singlet alkyl nitrenes How the immediate molecular environment determines the singlet photoproduct formation In chapter 02, we explore photoreactivity of methyl benzophenone with azido modification to study the behavior of benzophenone chromophore and azido chromophore at room temperature/cryogenic temperature. In chapter 03, we report the high quantum yield photorelease of azidomethyl benzophenone based Photoremovable protecting group (PRPG). With azido functionalization at 2’methyl position allows formed 1,4 biradical undergo expulsion of N2 to give rise to the irreversible imine biradical that make the photorelease reaction much efficient. Further, the azidomethyl substituted butyrophenone ester which is an acetophenone based counterpart of the benzophenone based PRPG was identified as an unsuccessful PRPG candidate. In chapter 04, we investigated two different photoprecursors that could generate same aryl nitrene upon photolysis. Compound 2-azidobenzphenone which includes inbuilt triplet sensitizer found to be generating triplet aryl nitrene in room and cryogenic temperature conditions. The 3-phenylbenzisoxazole which does not carry a triplet sensitizer found to be generating singlet nitrene at room temperature and at cryogenic temperature we detected the formation of triplet aryl nitrene. In Chapter 05, we considered vinylnitrene stability at room and low temperature using 5,6-dihydro-3-phenyl-4-H-cyclohex[c]isoxazole. Based on the experimental and computational evidences, we theorize that the unique reactivity of undetected triplet vinylnitreneTN is due to flexibility which reflects their 1,3-biradical character. In chapter 06, we rationalized the factors that determining photoproduct formation from singlet alkyl nitrenes based on immediate environment of the nitrene. In our present molecule, we have both ring and migratable phenyl group and photolysis results indicated that at room temperature, migration product is favored over ring expansion product.
Anna Gudmundsdottir, Ph.D. (Committee Chair)
Ruxandra Dima, Ph.D. (Committee Member)
James Mack, Ph.D. (Committee Member)
446 p.
Organic Chemistry
Laser Flash Photolysis; ESR; Photochemistry; Nitrenes; Photoremovable protecting groups; Matrix isolation

Recommended Citations

Citations

  • Thenna Hewa, K. R. S. (2017). Applications Focused Synthetic Modification on Photoremovable Protecting Groups (PRPG) & Photochemical Analysis on Organic Azides and Isoxazoles [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1511858669354976

    APA Style (7th edition)

  • Thenna Hewa, Kosala. Applications Focused Synthetic Modification on Photoremovable Protecting Groups (PRPG) & Photochemical Analysis on Organic Azides and Isoxazoles. 2017. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1511858669354976.

    MLA Style (8th edition)

  • Thenna Hewa, Kosala. "Applications Focused Synthetic Modification on Photoremovable Protecting Groups (PRPG) & Photochemical Analysis on Organic Azides and Isoxazoles." Doctoral dissertation, University of Cincinnati, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1511858669354976

    Chicago Manual of Style (17th edition)

ucin1511858669354976
56
© 2017, some rights reserved.Creative Commons License Applications Focused Synthetic Modification on Photoremovable Protecting Groups (PRPG) & Photochemical Analysis on Organic Azides and Isoxazoles by Kosala R. S. Thenna Hewa is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Cincinnati and OhioLINK.