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Article: "Bright" and "dark" excited states of an alternating at oligomer characterized by femtosecond broadband spectroscopy

Title"Bright" and "dark" excited states of an alternating at oligomer characterized by femtosecond broadband spectroscopy
Authors
Issue Date2009
PublisherAmerican Chemical Society. The Journal's web site is located at http://pubs.acs.org/journal/jpcbfk
Citation
Journal Of Physical Chemistry B, 2009, v. 113 n. 33, p. 11527-11534 How to Cite?
AbstractThe nature and dynamics of DNA excited states is of pivotal importance in determining both DNA ultraviolet photostability and its vulnerability toward photodamage. The complexity regarding the involvement of "bright" and "dark" excited states, their molecular origin, and the roles played by these states in the course of electronic energy relaxation constitute an active and contentious area in current research of DNA excited states. As a case study, we report here a combined broadband femtosecond time-resolved fluorescence (TRF) and transient absorption (TA) study on a self-complementary d(AT)10 oligomer and a reference system of an equal molar mixture of the constituent bases represented by adenosine and thymidine (A+T). Comparison of the spectral character and temporal evolution of the TRF and TA data for 267 nm excited d(AT)10 and A+T provides evidence for a base-localized excitation feature for an early (<∼50 fs) "bright" S LE state and its ensuing evolution within ∼3 ps into a ∼72 ps "dark" SE exciplex in d(AT)10. Combined analysis of the d(AT)10 TRF and TA results suggests the presence of a weakly fluorescent transient SG state that acts as a gateway to mediate the excitation transfer and energy elimination. A distinct base conformation- dependent model involving an ultrafast ∼0.3 ps conversion of the S LE to SG that then evolves by ∼3 ps into the S E has been proposed to account for the collective deactivation character of d(AT)10. This presents a novel excited-state picture that can unify the seemingly conflicting time-resolved results reported previously for related AT DNAs. The direct spectral and dynamical data provided here contributes important photophysical parameters for the description of the excited states of AT oligomers. The possible connection between the energy transfer giving the SE and the photostability vs photodamage of A/T DNAs is briefly discussed. © 2009 American Chemical Society.
Persistent Identifierhttp://hdl.handle.net/10722/69620
ISSN
2015 Impact Factor: 3.187
2015 SCImago Journal Rankings: 1.414
ISI Accession Number ID
Funding AgencyGrant Number
Research Grams Council of Hong KongPolyU/7029/06P
PolyU/7029/07P
PolyU/5007/08P
HKU/7040/06P
HKU 1/01C
Funding Information:

This research was done in the HKU Ultrafast Laser Facility. The authors thank the Research Grams Council of Hong Kong (PolyU/7029/06P, PolyU/7029/07P and PolyU/5007/08P to W.M.K. and HKU/7040/06P and HKU 1/01C to D.L.P.) for the financial support.

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DC FieldValueLanguage
dc.contributor.authorKwok, WMen_HK
dc.contributor.authorMa, Cen_HK
dc.contributor.authorPhillips, DLen_HK
dc.date.accessioned2010-09-06T06:15:20Z-
dc.date.available2010-09-06T06:15:20Z-
dc.date.issued2009en_HK
dc.identifier.citationJournal Of Physical Chemistry B, 2009, v. 113 n. 33, p. 11527-11534en_HK
dc.identifier.issn1520-6106en_HK
dc.identifier.urihttp://hdl.handle.net/10722/69620-
dc.description.abstractThe nature and dynamics of DNA excited states is of pivotal importance in determining both DNA ultraviolet photostability and its vulnerability toward photodamage. The complexity regarding the involvement of "bright" and "dark" excited states, their molecular origin, and the roles played by these states in the course of electronic energy relaxation constitute an active and contentious area in current research of DNA excited states. As a case study, we report here a combined broadband femtosecond time-resolved fluorescence (TRF) and transient absorption (TA) study on a self-complementary d(AT)10 oligomer and a reference system of an equal molar mixture of the constituent bases represented by adenosine and thymidine (A+T). Comparison of the spectral character and temporal evolution of the TRF and TA data for 267 nm excited d(AT)10 and A+T provides evidence for a base-localized excitation feature for an early (<∼50 fs) "bright" S LE state and its ensuing evolution within ∼3 ps into a ∼72 ps "dark" SE exciplex in d(AT)10. Combined analysis of the d(AT)10 TRF and TA results suggests the presence of a weakly fluorescent transient SG state that acts as a gateway to mediate the excitation transfer and energy elimination. A distinct base conformation- dependent model involving an ultrafast ∼0.3 ps conversion of the S LE to SG that then evolves by ∼3 ps into the S E has been proposed to account for the collective deactivation character of d(AT)10. This presents a novel excited-state picture that can unify the seemingly conflicting time-resolved results reported previously for related AT DNAs. The direct spectral and dynamical data provided here contributes important photophysical parameters for the description of the excited states of AT oligomers. The possible connection between the energy transfer giving the SE and the photostability vs photodamage of A/T DNAs is briefly discussed. © 2009 American Chemical Society.en_HK
dc.languageengen_HK
dc.publisherAmerican Chemical Society. The Journal's web site is located at http://pubs.acs.org/journal/jpcbfken_HK
dc.relation.ispartofJournal of Physical Chemistry Ben_HK
dc.title"Bright" and "dark" excited states of an alternating at oligomer characterized by femtosecond broadband spectroscopyen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=1520-6106&volume=113&spage=11527&epage=11534&date=2009&atitle=Bright”+and+“Dark”+Excited+States+of+an+Alternating+AT+Oligomer+Characterized+by+Femtosecond+Broadband+Spectroscopyen_HK
dc.identifier.emailMa, C:macs@hkucc.hku.hken_HK
dc.identifier.emailPhillips, DL:phillips@hku.hken_HK
dc.identifier.authorityMa, C=rp00758en_HK
dc.identifier.authorityPhillips, DL=rp00770en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1021/jp906265cen_HK
dc.identifier.pmid19719260-
dc.identifier.scopuseid_2-s2.0-70349233899en_HK
dc.identifier.hkuros170217en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-70349233899&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume113en_HK
dc.identifier.issue33en_HK
dc.identifier.spage11527en_HK
dc.identifier.epage11534en_HK
dc.identifier.isiWOS:000268907600023-
dc.publisher.placeUnited Statesen_HK
dc.relation.projectUltrafast laser facility for investigations of novel electronic excited states and intermediates in inorganic photochemistry, semiconductor materials and nanomaterials-
dc.identifier.scopusauthoridKwok, WM=7103129332en_HK
dc.identifier.scopusauthoridMa, C=7402924979en_HK
dc.identifier.scopusauthoridPhillips, DL=7404519365en_HK

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