Building model systems to understand Proton-Coupled Electron Transfer in heme : spectroscopic investigation of charge transfer to axially bound diimide acceptors

Proton-Coupled Electron Transfer (PCET) is an important mechanistic motif in chemistry, which allows for efficient charge transport in many biological systems. We seek to understand how the proton and electron motions are coupled in a bidirectional system allowing for individual turning of the kinetics and thermodynamics. The target of interest is a biomimedic heme system allowing for a detailed mechanistic study of the formation of the oxidation states of heme, of particular interest the highly reactive Fe(IV)=O species. The bidirectional model is prepared using a hangman porphyrin with an axially coordinated to the metal center, and the electron transfer event is triggered by excitation of the porphyrin. The synthesis of this motif is discussed as well as initial studies into the binding of a coordinated electron acceptor to the metal center. In the future, the excited state of the acceptor will be used to trigger the electron transfer portion of the PCET event. To understand the signatures of different electron acceptors and binding to the metal center, a redox inactive zinc porphyrin is used as a model to allow for longer excited state lifetimes and well known transient signatures. Three diimide acceptors have been coordinated through a pyridine ring to the metal center of the porphyrin, and electron transfer was triggered both by excitation of the porphyrin and the acceptor. Lifetimes of the charge separated state were determined using picoseconds and nanosecond transient absorption. The acceptors are then coordinated to a symmetrical iron porphyrin in an attempt to understand the behavior of charge separation in the more complicated open d shell system. Spectroscopic data of both systems is shown.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Chemistry.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2013

Author dc:creator

• Hanson, Christina J

Advisor dc:contributor.advisor

• Daniel G. Nocera.

• Chemistry.

Statement dc:rights

• 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.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/79268

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/79268