Excited state dynamics in DNA double helices

TL;DR

This study uses a quantum mechanical lattice model to analyze how photoexcited states behave in DNA, revealing that base type influences exciton stability and charge separation over femtoseconds.

Contribution

It introduces a combined intrachain and interchain electronic interaction model to simulate DNA exciton dynamics, highlighting base-specific behaviors.

Findings

Adenosine excitons remain cohesive on the same chain for hundreds of femtoseconds.

Thymidine excitons decompose into mobile charge carriers rapidly.

Charge mobility differences explain the distinct exciton behaviors.

Abstract

Recent ultrafast experiments have implicated that intrachain base-stacking rather than base-pairing mediate the fate and transport of photoexcited species in DNA chains. Here use an $SU(2)\otimes SU(2)$ lattice model which incorporates both intrachain and interchain electronic interactions to study the quantum mechanical evolution of an initial excitonic state placed on either the adenosine or thymidine side of a model B DNA poly(dA).poly(dT) duplex. Our calculations indicate that over several hundred femtoseconds, the adenosine exciton remains a cohesive excitonic wave packet on the adenosine side of the chain where as the thymidine exciton rapidly decomposes into mobile electron/hole pairs along the thymidine side of the chain. In both cases, the very little transfer to the other chain is seen over the time-scale of our calculations. We attribute the difference in these dynamics to the roughly 4:1 ratio of hole vs. electron mobility along the thymidine chain.