4.8 Article

Ultrafast Fluorescence Depolarization in Conjugated Polymers

Journal

JOURNAL OF PHYSICAL CHEMISTRY LETTERS
Volume 12, Issue 22, Pages 5344-5348

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acs.jpclett.1c01354

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Funding

  1. EPSRC Centre for Doctoral Training, Theory and Modelling in Chemical Sciences [EP/L015722/1]

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This study investigates the intrachain exciton dynamics in poly(para-phenylenevinylene) through large-scale simulations. The entanglement between excitons and C-C bond phonons causes exciton-site decoherence after photoexcitation, while torsional relaxation further leads to exciton-density localization.
We report on large-scale simulations of intrachain exciton dynamics in poly(para-phenylenevinylene). Our theoretical model describes Frenkel exciton coupling to both fast, quantized C-C bond vibrations and slow, classical torsional modes. We also incorporate system-bath interactions. The dynamics is simulated using the time evolution block decimation method, which avoids the failures of the Ehrenfest approximation to describe decoherence processes and nonadiabatic interstate conversion. System-bath interactions are modeled using quantum trajectories and Lindblad quantum jump operators. We find that following photoexcitation, the quantum mechanical entanglement of the exciton and C-C bond phonons causes exciton-site decoherence. Next, system-bath interactions cause the stochastic collapse of high-energy delocalized excitons into chromophores. Finally, torsional relaxation causes additional exciton-density localization. We relate these dynamical processes to the predicted fluorescence depolarization, extract the time scales corresponding to them, and thus interpret the observed sub-ps fluorescence depolarization.

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