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Article: A time-resolved spectroscopic study of the bichromophoric phototrigger 3',5'-dimethoxybenzoin diethyl phosphate: Interaction between the two chromophores determines the reaction pathway

TitleA time-resolved spectroscopic study of the bichromophoric phototrigger 3',5'-dimethoxybenzoin diethyl phosphate: Interaction between the two chromophores determines the reaction pathway
Authors
KeywordsChromophores
Dimethoxybenzoin
Photochemistry
Raman spectroscopy
Time-resolved spectroscopy
Issue Date2010
PublisherWiley - V C H Verlag GmbH & Co KGaA. The Journal's web site is located at http://www.wiley-vch.de/home/chemistry
Citation
Chemistry - A European Journal, 2010, v. 16 n. 17, p. 5102-5118 How to Cite?
Abstract3',5'-Dimethoxybenzoin (DMB) is a bichromophoric system that has widespread application as a highly efficient photoremovable protecting group (PRPG) for the release of diverse functional groups. The photodeprotection of DMB phototriggers is remarkably clean, and is accompanied by the formation of a biologically benign cyclization product, 3',5'-dimethoxybenzofuran (DMBF). The underlying mechanism of the DMB deprotection and cyclization has, however, until now remained unclear. Femtosecond transient absorption (fs-TA) spectroscopy and nanosecond time-resolved resonance Raman (ns-TR 3) spectroscopy were employed to detect the transient species directly, and examine the dynamic transformations involved in the primary photoreactions for DMB diethyl phosphate (DMBDP) in acetonitrile (CH 3CN). To assess the electronic character and the role played by the individual sub-chromophore, that is, the benzoyl, and the di-meta-methoxybenzylic moieties, for the DMBDP deprotection, comparative fsTA measurements were also carried out for the reference compounds diethyl phosphate acetophenone (DPAP), and 3',5'-dimethoxybenzylic diethyl phosphate (DMBnDP) in the same solvent. Comparison of the fs-TA spectra reveals that the photoexcited DMBDP exhibits distinctly different spectral character and dynamic evolution from those of the reference compounds. This fact, combined with the related steadystate spectral and density functional theoretical results, strongly suggests the presence in DMBDP of a significant interaction between the two sub-chromophores, and that this interaction plays a governing role in determining the nature of the photoexcitation and the reaction channel of the subsequent photophysical and photochemical transformations. The ns-TR 3 results and their correlation with the fs-TA spectra and dynamics provide evidence for a novel concerted deprotection-cyclization mechanism for DMBDP in CH 1CN. By monitoring the direct generation of the transient DMBF product, the cyclization time constant was determined unequivocally to be <1 ns. This indicates that there is little relevance for the long-lived intermediates (>10 ns) in giving the DMBF product, and excludes the stepwise mechanism proposed in the literature as the major pathway for the DMB cyclization reaction. This work provides important new insights into the origin of the 3',5'-dimethoxy substitution effect for the DMB photodeprotection. It also helps to clarify the many different views presented in previous mechanistic studies of the DMB PRPGs. In addition to this, our fs-TA results on the reference compound DMBnDP in CH 3CN provide the first direct observation (to the best of our knowledge) showing the predominance of a prompt (<2ps) heterolytic bond cleavage after photoexcitation of mefa-methoxybenzylic compounds. This provides insight into the long-term controversies about the photoinitiated dissociation mode of related substituted benzylic compounds. © 2010 Wiley-VCH Verlag GmbH & Cu. KGaA.
Persistent Identifierhttp://hdl.handle.net/10722/134722
ISSN
2015 Impact Factor: 5.771
2015 SCImago Journal Rankings: 2.323
ISI Accession Number ID
Funding AgencyGrant Number
Research Grants Council of Hong KongFIKU 1/01C
HKU 7039107P
Funding Information:

This research was carried out in the Ultrafast Laser Facility at the University of Hong Kong and supported by grants from the Research Grants Council of Hong Kong (FIKU 1/01C and HKU 7039107P) to D.L.P. and (PolyU 7029/06P and PolyU 7029107P) to W.M.K. D.L.P. thanks the Croucher Foundation for the Award of a Senior Research Fellowship and the University of Hong Kong for the Outstanding Researcher Award.

References

 

DC FieldValueLanguage
dc.contributor.authorChensheng, Men_HK
dc.contributor.authorKwok, WMen_HK
dc.contributor.authorAn, HYen_HK
dc.contributor.authorGuan, Xen_HK
dc.contributor.authorFu, MYen_HK
dc.contributor.authorToy, PHen_HK
dc.contributor.authorPhillips, DLen_HK
dc.date.accessioned2011-07-12T03:57:39Z-
dc.date.available2011-07-12T03:57:39Z-
dc.date.issued2010en_HK
dc.identifier.citationChemistry - A European Journal, 2010, v. 16 n. 17, p. 5102-5118en_HK
dc.identifier.issn0947-6539en_HK
dc.identifier.urihttp://hdl.handle.net/10722/134722-
dc.description.abstract3',5'-Dimethoxybenzoin (DMB) is a bichromophoric system that has widespread application as a highly efficient photoremovable protecting group (PRPG) for the release of diverse functional groups. The photodeprotection of DMB phototriggers is remarkably clean, and is accompanied by the formation of a biologically benign cyclization product, 3',5'-dimethoxybenzofuran (DMBF). The underlying mechanism of the DMB deprotection and cyclization has, however, until now remained unclear. Femtosecond transient absorption (fs-TA) spectroscopy and nanosecond time-resolved resonance Raman (ns-TR 3) spectroscopy were employed to detect the transient species directly, and examine the dynamic transformations involved in the primary photoreactions for DMB diethyl phosphate (DMBDP) in acetonitrile (CH 3CN). To assess the electronic character and the role played by the individual sub-chromophore, that is, the benzoyl, and the di-meta-methoxybenzylic moieties, for the DMBDP deprotection, comparative fsTA measurements were also carried out for the reference compounds diethyl phosphate acetophenone (DPAP), and 3',5'-dimethoxybenzylic diethyl phosphate (DMBnDP) in the same solvent. Comparison of the fs-TA spectra reveals that the photoexcited DMBDP exhibits distinctly different spectral character and dynamic evolution from those of the reference compounds. This fact, combined with the related steadystate spectral and density functional theoretical results, strongly suggests the presence in DMBDP of a significant interaction between the two sub-chromophores, and that this interaction plays a governing role in determining the nature of the photoexcitation and the reaction channel of the subsequent photophysical and photochemical transformations. The ns-TR 3 results and their correlation with the fs-TA spectra and dynamics provide evidence for a novel concerted deprotection-cyclization mechanism for DMBDP in CH 1CN. By monitoring the direct generation of the transient DMBF product, the cyclization time constant was determined unequivocally to be <1 ns. This indicates that there is little relevance for the long-lived intermediates (>10 ns) in giving the DMBF product, and excludes the stepwise mechanism proposed in the literature as the major pathway for the DMB cyclization reaction. This work provides important new insights into the origin of the 3',5'-dimethoxy substitution effect for the DMB photodeprotection. It also helps to clarify the many different views presented in previous mechanistic studies of the DMB PRPGs. In addition to this, our fs-TA results on the reference compound DMBnDP in CH 3CN provide the first direct observation (to the best of our knowledge) showing the predominance of a prompt (<2ps) heterolytic bond cleavage after photoexcitation of mefa-methoxybenzylic compounds. This provides insight into the long-term controversies about the photoinitiated dissociation mode of related substituted benzylic compounds. © 2010 Wiley-VCH Verlag GmbH & Cu. KGaA.en_HK
dc.languageeng-
dc.publisherWiley - V C H Verlag GmbH & Co KGaA. The Journal's web site is located at http://www.wiley-vch.de/home/chemistryen_HK
dc.relation.ispartofChemistry - A European Journalen_HK
dc.subjectChromophoresen_HK
dc.subjectDimethoxybenzoinen_HK
dc.subjectPhotochemistryen_HK
dc.subjectRaman spectroscopyen_HK
dc.subjectTime-resolved spectroscopyen_HK
dc.titleA time-resolved spectroscopic study of the bichromophoric phototrigger 3',5'-dimethoxybenzoin diethyl phosphate: Interaction between the two chromophores determines the reaction pathwayen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0947-6539&volume=16&issue=17&spage=5102&epage=5118&date=2010&atitle=A+time-resolved+spectroscopic+study+of+the+bichromophoric+phototrigger+3%27,5%27-dimethoxybenzoin+diethyl+phosphate:+Interaction+between+the+two+chromophores+determines+the+reaction+pathway-
dc.identifier.emailChensheng, M:macs@hkucc.hku.hken_HK
dc.identifier.emailToy, PH:phtoy@hkucc.hku.hken_HK
dc.identifier.emailPhillips, DL:phillips@hku.hken_HK
dc.identifier.authorityChensheng, M=rp00758en_HK
dc.identifier.authorityToy, PH=rp00791en_HK
dc.identifier.authorityPhillips, DL=rp00770en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1002/chem.200902891en_HK
dc.identifier.pmid20349465-
dc.identifier.scopuseid_2-s2.0-77951614904en_HK
dc.identifier.hkuros172141-
dc.identifier.hkuros170475-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-77951614904&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume16en_HK
dc.identifier.issue17en_HK
dc.identifier.spage5102en_HK
dc.identifier.epage5118en_HK
dc.identifier.eissn1521-3765-
dc.identifier.isiWOS:000277810800020-
dc.publisher.placeGermanyen_HK
dc.identifier.scopusauthoridChensheng, M=7402924979en_HK
dc.identifier.scopusauthoridKwok, WM=7103129332en_HK
dc.identifier.scopusauthoridAn, HY=54411879800en_HK
dc.identifier.scopusauthoridGuan, X=8313149700en_HK
dc.identifier.scopusauthoridFu, MY=24576708700en_HK
dc.identifier.scopusauthoridToy, PH=7006579247en_HK
dc.identifier.scopusauthoridPhillips, DL=7404519365en_HK

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