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Photochemical α-Cleavage Reaction of 3’,5’-Dimethoxybenzoin: A Combined Time-Resolved Spectroscopy and Computational Chemistry Study

Benzoin is one of the most commonly used photoinitiators to induce free radical polymerization. Here, improved benzoin properties could be accomplished by the introduction of two methoxy substituents, leading to the formation of 3’,5’-dimethoxybenzoin (DMB) which has a higher photo-cleavage quantum...

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Autores principales: Li, Yuanchun, Zhang, Xiting, Yan, Zhiping, Du, Lili, Tang, Wenjian, Phillips, David Lee
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7435414/
https://www.ncbi.nlm.nih.gov/pubmed/32756525
http://dx.doi.org/10.3390/molecules25153548
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author Li, Yuanchun
Zhang, Xiting
Yan, Zhiping
Du, Lili
Tang, Wenjian
Phillips, David Lee
author_facet Li, Yuanchun
Zhang, Xiting
Yan, Zhiping
Du, Lili
Tang, Wenjian
Phillips, David Lee
author_sort Li, Yuanchun
collection PubMed
description Benzoin is one of the most commonly used photoinitiators to induce free radical polymerization. Here, improved benzoin properties could be accomplished by the introduction of two methoxy substituents, leading to the formation of 3’,5’-dimethoxybenzoin (DMB) which has a higher photo-cleavage quantum yield (0.54) than benzoin (0.35). To elucidate the underlying reaction mechanisms of DMB and obtain direct information of the transient species involved, femtosecond transient absorption (fs-TA) and nanosecond transient absorption (ns-TA) spectroscopic experiments in conjunction with density functional theory/time-dependent density functional theory (DFT/TD-DFT) calculations were performed. It was found that the photo-induced α-cleavage (Norrish Type I reaction) of DMB occurred from the nπ* triplet state after a rapid intersystem crossing (ISC) process (7.6 ps), leading to the generation of phenyl radicals on the picosecond time scale. Compared with Benzoin, DMB possesses two methoxy groups which are able to stabilize the alcohol radical and thus result in a stronger driving force for cleavage and a higher quantum yield of photodissociation. Two stable conformations (cis-DMB and trans-DMB) at ground state were found via DFT calculations. The influence of the intramolecular hydrogen bond on the α-cleavage of DMB was elaborated.
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spelling pubmed-74354142020-08-28 Photochemical α-Cleavage Reaction of 3’,5’-Dimethoxybenzoin: A Combined Time-Resolved Spectroscopy and Computational Chemistry Study Li, Yuanchun Zhang, Xiting Yan, Zhiping Du, Lili Tang, Wenjian Phillips, David Lee Molecules Article Benzoin is one of the most commonly used photoinitiators to induce free radical polymerization. Here, improved benzoin properties could be accomplished by the introduction of two methoxy substituents, leading to the formation of 3’,5’-dimethoxybenzoin (DMB) which has a higher photo-cleavage quantum yield (0.54) than benzoin (0.35). To elucidate the underlying reaction mechanisms of DMB and obtain direct information of the transient species involved, femtosecond transient absorption (fs-TA) and nanosecond transient absorption (ns-TA) spectroscopic experiments in conjunction with density functional theory/time-dependent density functional theory (DFT/TD-DFT) calculations were performed. It was found that the photo-induced α-cleavage (Norrish Type I reaction) of DMB occurred from the nπ* triplet state after a rapid intersystem crossing (ISC) process (7.6 ps), leading to the generation of phenyl radicals on the picosecond time scale. Compared with Benzoin, DMB possesses two methoxy groups which are able to stabilize the alcohol radical and thus result in a stronger driving force for cleavage and a higher quantum yield of photodissociation. Two stable conformations (cis-DMB and trans-DMB) at ground state were found via DFT calculations. The influence of the intramolecular hydrogen bond on the α-cleavage of DMB was elaborated. MDPI 2020-08-03 /pmc/articles/PMC7435414/ /pubmed/32756525 http://dx.doi.org/10.3390/molecules25153548 Text en © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Li, Yuanchun
Zhang, Xiting
Yan, Zhiping
Du, Lili
Tang, Wenjian
Phillips, David Lee
Photochemical α-Cleavage Reaction of 3’,5’-Dimethoxybenzoin: A Combined Time-Resolved Spectroscopy and Computational Chemistry Study
title Photochemical α-Cleavage Reaction of 3’,5’-Dimethoxybenzoin: A Combined Time-Resolved Spectroscopy and Computational Chemistry Study
title_full Photochemical α-Cleavage Reaction of 3’,5’-Dimethoxybenzoin: A Combined Time-Resolved Spectroscopy and Computational Chemistry Study
title_fullStr Photochemical α-Cleavage Reaction of 3’,5’-Dimethoxybenzoin: A Combined Time-Resolved Spectroscopy and Computational Chemistry Study
title_full_unstemmed Photochemical α-Cleavage Reaction of 3’,5’-Dimethoxybenzoin: A Combined Time-Resolved Spectroscopy and Computational Chemistry Study
title_short Photochemical α-Cleavage Reaction of 3’,5’-Dimethoxybenzoin: A Combined Time-Resolved Spectroscopy and Computational Chemistry Study
title_sort photochemical α-cleavage reaction of 3’,5’-dimethoxybenzoin: a combined time-resolved spectroscopy and computational chemistry study
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7435414/
https://www.ncbi.nlm.nih.gov/pubmed/32756525
http://dx.doi.org/10.3390/molecules25153548
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