Non-adiabatic molecular dynamics investigation of the size dependence of the electronic relaxation in polyacenes

Evgeny Posenitskiy 1 Mathias Rapacioli 2 Bruno Lepetit 1 Didier Lemoine 1 Fernand Spiegelman 2
1 Théorie (LCAR)
LCAR - Laboratoire Collisions Agregats Reactivite
2 Modélisation, Agrégats, Dynamique (LCPQ)
LCPQ - Laboratoire de Chimie et Physique Quantiques
Abstract : The Tully's fewest switches surface hopping algorithm is implemented within the framework of the time-dependent density functional based tight binding method (TD-DFTB) to simulate the energy relaxation following absorption of a UV photon by polycyclic aromatic hydrocarbons (PAHs). This approach is used to study the size effect on the ultrafast dynamics in excited states for a special class of PAH species called polyacenes. We determine the dynamical relaxation times and discuss the underlying mechanisms. Our results show that there is a striking alternation in decay times of the brightest singlet state for neutral polyacenes with 3 to 6 aromatic cycles. The alternation corresponds to an order-of-magnitude variation between roughly 10 and 100 fs and is correlated with a qualitatively similar alternation of energy gaps between the brightest state and the state lying just below in energy.
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Evgeny Posenitskiy, Mathias Rapacioli, Bruno Lepetit, Didier Lemoine, Fernand Spiegelman. Non-adiabatic molecular dynamics investigation of the size dependence of the electronic relaxation in polyacenes. Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2019, 21, pp.12139-12149. ⟨10.1039/C9CP00603F⟩. ⟨hal-02156273⟩

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