We report on high-dimensional quantum dynamical simulations of
torsion-induced exciton migration in a single-chain oligothiophene segment
comprising twenty repeat units, using a first-principles parametrized Frenkel
J-aggregate Hamiltonian. Starting from an initial inter-ring torsional defect,
these simulations provide evidence of an ultrafast two-time scale process at
low temperatures, involving exciton-polaron formation within tens of
femtoseconds, followed by torsional relaxation on a ~300 femtosecond time
scale. The second step is the driving force for exciton migration, as initial
conjugation breaks are removed by dynamical planarization. The quantum coherent
nature of the elementary exciton migration step is consistent with experimental
observations highlighting the correlated and vibrationally coherent nature of
the dynamics on ultrafast time scales.Comment: 4 pages, 4 figure
