Ultrafast Exciton Self-Trapping upon Geometry Deformation in Perylene-Based Molecular Aggregates

J Phys Chem Lett. 2013 Mar 7;4(5):792-6. doi: 10.1021/jz4000752. Epub 2013 Feb 21.

Abstract

Femtosecond time-resolved experiments demonstrate that the photoexcited state of perylene tetracarboxylic acid bisimide (PBI) aggregates in solution decays nonradiatively on a time-scale of 215 fs. High-level electronic structure calculations on dimers point toward the importance of an excited state intermolecular geometry distortion along a reaction coordinate that induces energy shifts and couplings between various electronic states. Time-dependent wave packet calculations incorporating a simple dissipation mechanism indicate that the fast energy quenching results from a doorway state with a charge-transfer character that is only transiently populated. The identified relaxation mechanism corresponds to a possible exciton trap in molecular materials.

Keywords: ab initio calculations; excitation energy transfer (EET); femtochemistry; photophysics; quantum dynamics.