Biradical radiationless decay channel in adenine and its derivatives

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DOIResolve DOI: http://doi.org/10.1139/v07-006
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TypeArticle
Journal titleCanadian Journal of Chemistry
ISSN0008-4042
1480-3291
Volume85
Issue2
Pages124134; # of pages: 11
Subjectadenine, guanine, DNA damage, radiationless decay, biradical, ab initio, coupled clusted
AbstractCoupled-cluster calculations of increasing accuracy (approximate doubles: CC2; doubles: EOM-CCSD; connected triples: CR-EOM-CCSD(T)) for CIS-optimized potential energy profiles of adenine and its derivatives indicate that the ultrafast internal conversion of the optically excited π π* state occurs through a state switch to a biradical state, which intersects the ground state at a lower energy. The electronic nature of the biradical state is defined by an electronic configuration in which one unpaired electron occupies a π* orbital confined to the five-membered ring. The second unpaired electron is localized very strongly on a p-type C2 atomic orbital of the six-membered ring. The biradical state minimum has a strongly puckered six-membered ring and a C2–H bond, which is twisted nearly perpendicular to the average ring plane. Consistent with the biradical-mediated internal conversion, the π π* state lifetime is extremely short in adenine and 9-methyladenine, which have barrierless crossing to the biradical state. The lifetime is slightly longer in N,N-dimethyladenine, which has a small barrier for the state switch. In 2-aminopurine the biradical state is found above the π π* state, preventing the biradical state switch and dramatically increasing the lifetime. These results, combined with an earlier work on pyrimidine bases, strongly suggest the importance of a direct decay of the doorway π π* state via a biradical state switch in the photophysics of DNA, even though the nature of the biradical state is somewhat different in purines and pyrimidines.
Publication date
PublisherNRC Research Press
LanguageEnglish
AffiliationNational Research Council Canada; NRC Steacie Institute for Molecular Sciences
Peer reviewedYes
NPARC number12328624
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Record identifier91cb9122-c111-42dc-abb4-eb2a1fbb23cf
Record created2009-09-10
Record modified2017-07-10
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