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Article: Unravelling the reaction mechanism for the fast photocyclisation of 2-benzoylpyridine in aqueous solvent by time-resolved spectroscopy and density functional theory calculations

TitleUnravelling the reaction mechanism for the fast photocyclisation of 2-benzoylpyridine in aqueous solvent by time-resolved spectroscopy and density functional theory calculations
Authors
KeywordsCyclization
Photochemistry
Raman spectroscopy
Reaction mechanisms
Solvent effects
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. 23, p. 6961-6972 How to Cite?
AbstractA combined femtosecond transient absorption (fs-TA) and nano-second time-resolved resonance Raman (ns-TR 3) spectroscopic investigation of the photoreaction of 2-benzoylpyridine (2-BPy) in acetonitrile and neutral, basic and acidic aqueous solvents is reported. fs-TA results showed that the nit* triplet 2-BPy is the precursor of the photocyclisation reaction in neutral and basic aqueous solvents. The cis triplet biradical and the cis singlet zwitterionic species produced during the photocyclisation reaction were initially characterised by ns-TR 3 spectroscopy. In addition, a new species was uniquely observed in basic aqueous solvent after the decay of the cis singlet zwitterionic species and this new species was tentatively assigned to the photocyclised radical anion. The ground-state conformation of 2-BPy in acidic aqueous solvent is the pyridine nitrogen-protonated 2-BPy cation (2BPy-NH +) rather than the neutral form of 2-BPy. After laser photolysis, the singlet excited state (Si) of 2-BPy-NH + is generated and evolves through excited-state proton transfer (ESPT) and efficient intersystem crossing (ISC) processes to the triplet exited state (T 1) of the carbonyl oxygen-protonated 2BPy cation (2-BPy-OH +) and then photocyclises with the lone pair of the nitrogen atom in the heterocyclic ring. Cyclisation reactions take place both in neutral/basic and acidic aqueous solvents, but the photocyclisation mechanisms in these different aqueous solvents are very different. This is likely due to the different conformation of the precursor and the influence of hydrogen-bonding of the solvent on the reactions. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Persistent Identifierhttp://hdl.handle.net/10722/142057
ISSN
2015 Impact Factor: 5.771
2015 SCImago Journal Rankings: 2.323
ISI Accession Number ID
Funding AgencyGrant Number
Research Grants Council of Hong KongHKU 7035/08P
HKU 1/01C
Croucher Foundation
University of Hong Kong
University of Rochester
Funding Information:

This work was supported by a grant from the Research Grants Council of Hong Kong (HKU 7035/08P and HKU 1/01C), the award of a Croucher Foundation Senior Research Fellowship (2006-07) front the Croucher Foundation and an Outstanding Researcher Award (2006) from the University of Hong Kong to D.L.P. Work performed at the University of Rochester was supported by start-up funding to D.W.M.

References
Grants

 

DC FieldValueLanguage
dc.contributor.authorDu, Yen_HK
dc.contributor.authorXue, Jen_HK
dc.contributor.authorLi, MDen_HK
dc.contributor.authorGuan, Xen_HK
dc.contributor.authorMcCamant, DWen_HK
dc.contributor.authorPhillips, DLen_HK
dc.date.accessioned2011-10-17T07:06:39Z-
dc.date.available2011-10-17T07:06:39Z-
dc.date.issued2010en_HK
dc.identifier.citationChemistry - A European Journal, 2010, v. 16 n. 23, p. 6961-6972en_HK
dc.identifier.issn0947-6539en_HK
dc.identifier.urihttp://hdl.handle.net/10722/142057-
dc.description.abstractA combined femtosecond transient absorption (fs-TA) and nano-second time-resolved resonance Raman (ns-TR 3) spectroscopic investigation of the photoreaction of 2-benzoylpyridine (2-BPy) in acetonitrile and neutral, basic and acidic aqueous solvents is reported. fs-TA results showed that the nit* triplet 2-BPy is the precursor of the photocyclisation reaction in neutral and basic aqueous solvents. The cis triplet biradical and the cis singlet zwitterionic species produced during the photocyclisation reaction were initially characterised by ns-TR 3 spectroscopy. In addition, a new species was uniquely observed in basic aqueous solvent after the decay of the cis singlet zwitterionic species and this new species was tentatively assigned to the photocyclised radical anion. The ground-state conformation of 2-BPy in acidic aqueous solvent is the pyridine nitrogen-protonated 2-BPy cation (2BPy-NH +) rather than the neutral form of 2-BPy. After laser photolysis, the singlet excited state (Si) of 2-BPy-NH + is generated and evolves through excited-state proton transfer (ESPT) and efficient intersystem crossing (ISC) processes to the triplet exited state (T 1) of the carbonyl oxygen-protonated 2BPy cation (2-BPy-OH +) and then photocyclises with the lone pair of the nitrogen atom in the heterocyclic ring. Cyclisation reactions take place both in neutral/basic and acidic aqueous solvents, but the photocyclisation mechanisms in these different aqueous solvents are very different. This is likely due to the different conformation of the precursor and the influence of hydrogen-bonding of the solvent on the reactions. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.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.subjectCyclizationen_HK
dc.subjectPhotochemistryen_HK
dc.subjectRaman spectroscopyen_HK
dc.subjectReaction mechanismsen_HK
dc.subjectSolvent effectsen_HK
dc.subjectTime-resolved spectroscopyen_HK
dc.titleUnravelling the reaction mechanism for the fast photocyclisation of 2-benzoylpyridine in aqueous solvent by time-resolved spectroscopy and density functional theory calculationsen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0947-6539&volume=16&issue=23&spage=6961&epage=6972&date=2010&atitle=Unravelling+the+reaction+mechanism+for+the+fast+photocyclisation+of+2-benzoylpyridine+in+aqueous+solvent+by+time-resolved+spectroscopy+and+density+functional+theory+calculations-
dc.identifier.emailPhillips, DL:phillips@hku.hken_HK
dc.identifier.authorityPhillips, DL=rp00770en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1002/chem.200903073en_HK
dc.identifier.pmid20437422-
dc.identifier.scopuseid_2-s2.0-77953584674en_HK
dc.identifier.hkuros181783-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-77953584674&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume16en_HK
dc.identifier.issue23en_HK
dc.identifier.spage6961en_HK
dc.identifier.epage6972en_HK
dc.identifier.isiWOS:000279856100029-
dc.publisher.placeGermanyen_HK
dc.relation.projectUltrafast laser facility for investigations of novel electronic excited states and intermediates in inorganic photochemistry, semiconductor materials and nanomaterials-
dc.identifier.scopusauthoridDu, Y=35310175500en_HK
dc.identifier.scopusauthoridXue, J=23007272500en_HK
dc.identifier.scopusauthoridLi, MD=7405265795en_HK
dc.identifier.scopusauthoridGuan, X=8313149700en_HK
dc.identifier.scopusauthoridMcCamant, DW=6505954265en_HK
dc.identifier.scopusauthoridPhillips, DL=7404519365en_HK

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