Mechanistic studies of photo-induced proton-coupled electron transfer and oxygen atom transfer reactions in model systems
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, February 2007.
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| Format: | Thesis |
| Language: | eng |
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Massachusetts Institute of Technology
2007
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| Online Access: | http://hdl.handle.net/1721.1/38539 |
| _version_ | 1826200169020915712 |
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| author | Hodgkiss, Justin M. (Justin Mark), 1978- |
| author2 | Daniel G. Nocera. |
| author_facet | Daniel G. Nocera. Hodgkiss, Justin M. (Justin Mark), 1978- |
| author_sort | Hodgkiss, Justin M. (Justin Mark), 1978- |
| collection | MIT |
| description | Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, February 2007. |
| first_indexed | 2024-09-23T11:32:13Z |
| format | Thesis |
| id | mit-1721.1/38539 |
| institution | Massachusetts Institute of Technology |
| language | eng |
| last_indexed | 2024-09-23T11:32:13Z |
| publishDate | 2007 |
| publisher | Massachusetts Institute of Technology |
| record_format | dspace |
| spelling | mit-1721.1/385392019-04-12T14:05:30Z Mechanistic studies of photo-induced proton-coupled electron transfer and oxygen atom transfer reactions in model systems Mechanistic studies of PCET and OAT reactions in model systems Hodgkiss, Justin M. (Justin Mark), 1978- Daniel G. Nocera. Massachusetts Institute of Technology. Dept. of Chemistry. Massachusetts Institute of Technology. Dept. of Chemistry. Chemistry. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, February 2007. This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. Vita. Includes bibliographical references. Time-resolved optical spectroscopy has been employed for mechanistic studies in model systems designed to undergo photo-induced proton-coupled electron transfer (PCET) and oxygen atom transfer (OAT) reactions, both of which are important to energy conversion chemistry (Chapter I). The effect of coupling proton transfer (PT) to electron transfer (ET) depends on their spatial configuration, thus model PCET systems must control both. Noncovalent amidinium-carboxylate PT interfaces are used assemble an electron D/A pairs (D = donor, A = acceptor), establishing uni-directional ET and PT coordinates. A highly conjugated porphyrin-amidinium derivative bears optical signatures that report on the structure of PT interfaces formed upon association with carboxylate acceptors (Chapter II). PT is supported within the interface and the mediating proton's position is sensitive to the peripheral electronic structure. Transient absorption (TA) spectroscopy is applied to a related porphyrin D---[H+]---A assembly, where ---[H+]--- = amidinecarboxylic acid (Chapter III). Specific probe wavelengths are targeted in order to amplify the optical signatures of PCET over those of competing quenching mechanisms. (cont.) The observed PCET rates are strongly attenuated compared with comparable covalentlybridged analogues, indicating that the PT interface reduces electronic coupling. Temperature-isotope dependence of the PCET rates reveals an unusual inverse isotope effect at low temperature, which is interpreted in a model of vibrationally-assisted PCET (chapter IV). Hangman porphyrin dyads have been developed to study bi-directional PCET in relation to oxygen activation. ET and PT coordinates are orthogonalized at fixed distances about a FeIII-OH center (Chapters V and VI). TA spectroscopy and electronic structure calculations reveal that the structural reorganization attendant to metal-centered PCET imposes a severe kinetic cost and alternative quenching pathways prevail. Finally, TA spectroscopy has been used to elucidate the mechanism of photocatalytic OAT for bridged diiron [mu]-oxo bisporphyrins (Chapter VII). The [mu]-oxo bond is photo-cleaved to generate a terminal iron(IV) oxo, which undergoes OAT to nucleophilic substrates. OAT rates are maximized when the bridge actively splays the porphyrin subunits apart to present the oxo before reclamping can occur. by Justin M. Hodgkiss. Ph.D. 2007-08-29T19:07:27Z 2007-08-29T19:07:27Z 2006 2007 Thesis http://hdl.handle.net/1721.1/38539 165119116 eng CDROM contains entire thesis in .PDF format. M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 266 p. application/pdf Massachusetts Institute of Technology |
| spellingShingle | Chemistry. Hodgkiss, Justin M. (Justin Mark), 1978- Mechanistic studies of photo-induced proton-coupled electron transfer and oxygen atom transfer reactions in model systems |
| title | Mechanistic studies of photo-induced proton-coupled electron transfer and oxygen atom transfer reactions in model systems |
| title_full | Mechanistic studies of photo-induced proton-coupled electron transfer and oxygen atom transfer reactions in model systems |
| title_fullStr | Mechanistic studies of photo-induced proton-coupled electron transfer and oxygen atom transfer reactions in model systems |
| title_full_unstemmed | Mechanistic studies of photo-induced proton-coupled electron transfer and oxygen atom transfer reactions in model systems |
| title_short | Mechanistic studies of photo-induced proton-coupled electron transfer and oxygen atom transfer reactions in model systems |
| title_sort | mechanistic studies of photo induced proton coupled electron transfer and oxygen atom transfer reactions in model systems |
| topic | Chemistry. |
| url | http://hdl.handle.net/1721.1/38539 |
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