Efficiencies of photoinduced electron-transfer reactions: role of the Marcus inverted region in return electron transfer within geminate radical-ion pairs

Gould, Ian R.; Ege, D.; Moser, Jacques-E.; Farid, Samir

doi:10.1021/ja00167a027

Cited by 463 publications

(439 citation statements)

References 0 publications

Supporting

Mentioning

413

Contrasting

Unclassified

Order By: Relevance

“…The slowing down of charge recombination with increasing energy of the exciplex state is seen for diverse geminate radical-ion pairs (24). It is consistent with the frequent observation that highly exothermic electron-transfer reactions frequently fall in the Marcus-inverted region.…”

Section: Discussionsupporting

confidence: 84%

UV excitation of single DNA and RNA strands produces high yields of exciplex states between two stacked bases

Takaya

Su²,

Harpe³

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

186

308

View full text Add to dashboard Cite

Excited electronic states created by UV excitation of the diribonucleoside monophosphates ApA, ApG, ApC, ApU, and CpG were studied by the femtosecond transient-absorption technique. Bleach recovery signals recorded at 252 nm show that long-lived excited states are formed in all five dinucleosides. The lifetimes of these states exceed those measured in equimolar mixtures of the constituent mononucleotides by one to two orders of magnitude, indicating that electronic coupling between proximal nucleobases dramatically slows the relaxation of excess electronic energy. The decay rates of the long-lived states decrease with increasing energy of the charge-transfer state produced by transferring an electron from one base to another. The charge-transfer character of the long-lived states revealed by this analysis supports their assignment to excimer or exciplex states. Identical bleach recovery signals were seen for ApA, (A) 4, and poly(A) at delay times >10 ps after photoexcitation. This indicates that excited states localized on a stack of just two bases are the common trap states independent of the number of stacked nucleotides. The fraction of initial excitations that decay to long-lived exciplex states is approximately equal to the fraction of stacked bases determined by NMR measurements. This supports a model in which excitations associated with two stacked bases decay to exciplex states, whereas excitations in unstacked bases decay via ultrafast internal conversion. These results establish the importance of charge transferquenching pathways for UV-irradiated RNA and DNA in roomtemperature solution.DNA excited states ͉ DNA photodamage ͉ electronic structure ͉ femtosecond spectroscopy E xcited electronic states created in DNA by UV light have been studied since the 1960s but have received a great deal of attention recently because of advances in experiment and theory (1). These efforts are motivated by the desire to understand the photoreactions behind the genetic damage induced by UV light. There is also increasing interest in DNA and other arrays of -stacked chromophores as materials for optoelectronic applications (2-4).Striking differences have emerged between the dynamics of excited states in single bases and those in base assemblies. Excited states of single nucleobases and mononucleotides decay to the ground state primarily by ultrafast internal conversion in several hundred femtoseconds (5, 6). The additional degrees of freedom in polymeric DNA might be expected to quench singlet excited states even more rapidly, but the lifetimes actually increase dramatically. Femtosecond transient absorption measurements reveal that excited states in oligo-and polynucleotides relax in tens to hundreds of picoseconds (1, 7-10).Although there is consensus that electronic relaxation can take place orders of magnitude more slowly in DNA polymers, contradictory assignments have been proposed for the long-lived states. assigned the long-lived excited states seen in (dA) 18 , (dA) 18 ⅐(dT) 18 , and (dAdT) 9 ⅐(dAdT) 9 , to exci...

show abstract

Section: Discussionsupporting

confidence: 84%

UV excitation of single DNA and RNA strands produces high yields of exciplex states between two stacked bases

Takaya

Su²,

Harpe³

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

186

308

View full text Add to dashboard Cite

show abstract

“…This effect has been invoked by Gould et al to explain the higher ion yields measured with naphthalene derivatives than with benzene derivatives as electron donors. 43 For the R-branched aliphatic amines, the charge delocalization increases with the size of the alkyl substituents. Thus, the hole density on the N atom decreases continuously from TEA to DIPPA, although the spin remains localized on N. This increasing hole dilution should lead to a corresponding decrease of the contribution of the p orbital at the N atom to BET and to a parallel decrease of V. The stabilization of the hole through delocalization is reflected by a decrease of the vertical ionization potential of the amines upon addition of alkyl substituents (aIP + ∆IP in Table 2).…”

Section: Discussionmentioning

confidence: 99%

Effect of Steric Hindrance on the Dynamics of Charge Recombination within Geminate Ion Pairs

Vauthey

2000

J. Phys. Chem. A

View full text Add to dashboard Cite

The dynamics of charge recombination within geminate ion pairs formed by electron transfer (ET) quenching of excited aromatic hydrocarbons by aliphatic and aromatic amines was investigated using picosecond transient grating spectroscopy. With aliphatic donors, the rate constant of back ET, k BET , shows a substantial decrease with increasing steric encumbrance around the N atom. No correlation between k BET and the exergonicity of the process was observed. This effect is ascribed to a decrease of the electronic coupling matrix element, V, which is affected by both the distance between the N atom of the donor and the aromatic plane of the acceptor and by the delocalization of the hole upon increasing the bulkiness of the alkyl substituents. With aromatic amines, k BET is substantially slower than with the unhindered amines. This is also explained in terms of a smaller value of V because of charge delocalization.

show abstract

“…radical ion pair than with 1a, since we are here in the inverted Marcus region]. 21 In conclusion, this work provides new examples of aromatic alkylations achieved through photoinduced electron transfer, and which occur via benzyl radical/arene radical cation combination instead of the known benzyl radical/arene radical anion interaction. Where SET is exothermic or moderately endothermic, the photocleavage of benzyl chlorides occurs in a way quite similar to that observed in electrochemistry, viz.…”

mentioning

confidence: 75%

Photoinduced benzylation of 1,4-dimethoxynaphthalene by benzyl halides

Albini¹,

Siviero²,

Mella³

et al. 1995

J. Chem. Soc., Perkin Trans. 2

View full text Add to dashboard Cite

Irradiation of 1,4-dimethoxynaphthalene (DMNH) in the presence of 4-substituted benzyl chlorides (X-C 6 H 4 CH 2 Cl, X = H, Cl, CN, or NO 2 ) in either acetonitrile or benzene solution results in benzylation of DMNH, predominantly at position 2 and to a lesser extent on the unsubstituted ring. Steady state and flash photolysis studies show that charge transfer between singlet excited DMNH and the chlorides is involved. The reaction occurs predominantly in-cage via concerted electron transfer and carbon-chlorine bond cleavage with X = H or Cl , while with X = NO 2 fragmentation of the benzyl chloride radical anion occurs out-of-cage, but the process in this case is much less efficient due to competing back electron transfer.--

show abstract

Efficiencies of photoinduced electron-transfer reactions: role of the Marcus inverted region in return electron transfer within geminate radical-ion pairs

Cited by 463 publications

References 0 publications

UV excitation of single DNA and RNA strands produces high yields of exciplex states between two stacked bases

UV excitation of single DNA and RNA strands produces high yields of exciplex states between two stacked bases

Effect of Steric Hindrance on the Dynamics of Charge Recombination within Geminate Ion Pairs

Photoinduced benzylation of 1,4-dimethoxynaphthalene by benzyl halides

Contact Info

Product

Resources

About