Frenkel Exciton Model of Ultrafast Excited State Dynamics in AT DNA Double Helices

TL;DR

This study uses a lattice model to investigate ultrafast exciton dynamics in DNA, revealing that excitons on adenine remain cohesive while thymine excitons quickly decompose into charge carriers, with minimal interchain transfer.

Contribution

The paper introduces an $SU(2)\otimes SU(2)$ lattice model that incorporates both intra- and interchain interactions to analyze DNA exciton dynamics, highlighting the importance of charge-transfer states.

Findings

Adenine excitons stay cohesive over hundreds of femtoseconds.

Thymine excitons rapidly decompose into electron/hole pairs.

Minimal interchain transfer observed during the simulation timeframe.

Abstract

Recent ultrafast experiments have implicated intrachain base-stacking rather than base-pairing as the crucial factor in determining the fate and transport of photoexcited species in DNA chains. An important issue that has emerged concerns whether or not a Frenkel excitons is sufficient one needs charge-transfer states to fully account for the dynamics. In we present 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. We also show that this difference is is robust even when structural fluctuations are introduced in the form of static off-diagonal disorder.