Abstract
The ultrafast time evolution of a single-stranded adenine DNA is studied using a hybrid multiscale quantum mechanics/molecular mechanics (QM/MM) scheme coupled to nonadiabatic surface hopping dynamics. As a model, we use (dA)20 where a stacked adenine tetramer is treated quantum chemically. The dynamical simulations combined with on-the-fly quantitative wave function analysis evidence the nature of the long-lived electronically excited states formed upon absorption of UV light. After a rapid decrease of the initially excited excitons, relaxation to monomer-like states and excimers occurs within 100 fs. The former monomeric states then relax into additional excimer states en route to forming stabilized charge-transfer states on a longer timescale of hundreds of femtoseconds. The different electronic-state characters is reflected on the spatial separation between the adenines: excimers and charge-transfer states show a much smaller spatial separation than the monomer-like states and the initially formed excitons.
Highlights
The ultrafast time evolution of a single-stranded adenine DNA is studied using a hybrid multiscale quantum mechanics/molecular mechanics (QM/MM) scheme coupled to nonadiabatic surface hopping dynamics
U nderstanding the impact that light has on DNA,[1] for instance, as photodamage on the genetic code,[2] requires the characterization of the electronically excited states created upon light absorption as well as their time evolution beyond the Franck−Condon region
The collective excited state behavior of DNA depends on a number of structural and electronic interactions, which are often interrogated with timeresolved spectroscopy and theory.[3−9] Stacking interactions between nucleobases is one important mechanism that affects the excited-state behavior of DNA versus isolated nucleobases and mononucleotides.[1,3,8,10,11]
Summary
The ultrafast time evolution of a single-stranded adenine DNA is studied using a hybrid multiscale quantum mechanics/molecular mechanics (QM/MM) scheme coupled to nonadiabatic surface hopping dynamics. A recent transient absorption spectroscopy study[24] on DNA single strands of adenine revealed the internal conversion of the initial exciton states within 100 fs, followed by a decrease in the interbase distance along with an increase in charge-transfer character of the excitation, which is stabilized within 3 ps.
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