Mesolytic Versus Homolytic Cleavage in Photochemical Nitroxide-Mediated Polymerization
- Nicholas S. HillNicholas S. HillARC Centre of Excellence for Electromaterials Science, Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 2601, AustraliaMore by Nicholas S. Hill
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- Melinda J. FuleMelinda J. FuleARC Centre of Excellence for Electromaterials Science, Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 2601, AustraliaMore by Melinda J. Fule
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- Jason Morris
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- Jean-Louis ClémentJean-Louis ClémentAix Marseille Univ, CNRS, ICR UMR 7273, 13397 Marseille, FranceMore by Jean-Louis Clément
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- Yohann GuillaneufYohann GuillaneufAix Marseille Univ, CNRS, ICR UMR 7273, 13397 Marseille, FranceMore by Yohann Guillaneuf
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- Didier Gigmes
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- Michelle L. Coote*Michelle L. Coote*E-mail: [email protected]ARC Centre of Excellence for Electromaterials Science, Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 2601, AustraliaMore by Michelle L. Coote
Abstract
Time-dependent density functional theory calculations have been performed to study the photocleavage reactions of chromophore-functionalized alkoxyamines in nitroxide-mediated photopolymerization. Two case studies were considered: azaphenalene derivatives and benzophenone-based alkoxyamines. For the azaphenalenes, we show that the expected homolysis pathway is actually inaccessible. Instead, these alkoxyamines exhibit low-lying nNπ* excited states that exhibit an electronic structure about the nitroxide moiety similar to that of the formally oxidized radical cation. As a result, the cleavage of these alkoxyamines can be described as mesolytic-like rather than homolytic. As with formally oxidized species, mesolytic cleavage can result in the production of either carbon-centered radicals or carbocations, with only the former resulting in radical polymerization. Here, the cleavage products are found to be dependent on the respective radical/cation stabilities of the monomer units of choice (styrene, ethyl propanoate, and ethyl isobutyrate). In contrast to the azaphenalenes, in the benzophenone-based alkoxyamines, conjugation between the nitroxide and chromophore moieties appears to facilitate homolysis because of the ideal alignment of singlet and triplet states of different symmetries.
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