Coherent exciton-vibrational dynamics and energy transfer in conjugated organics

Tammie R. Nelson, Dianelys Ondarse-Alvarez, Nicolas Oldani, Beatriz Rodriguez-Hernandez, Laura Alfonso-Hernandez, Johan F. Galindo, Valeria D. Kleiman, Sebastian Fernandez-Alberti, Adrian E. Roitberg, Sergei Tretiak

Coherence, signifying concurrent electron-vibrational dynamics in complex natural and man-made systems, is currently a subject of intense study. Understanding this phenomenon is important when designing carrier transport in optoelectronic materials. Here, excited state dynamics simulations reveal a ubiquitous pattern in the evolution of photoexcitations for a broad range of molecular systems. Symmetries of the wavefunctions define a specific form of the non-adiabatic coupling that drives quantum transitions between excited states, leading to a collective asymmetric vibrational excitation coupled to the electronic system. This promotes periodic oscillatory evolution of the wavefunctions, preserving specific phase and amplitude relations across the ensemble of trajectories. The simple model proposed here explains the appearance of coherent exciton-vibrational dynamics due to non-adiabatic transitions, which is universal across multiple molecular systems. The observed relationships between electronic wavefunctions and the resulting functionalities allows us to understand, and potentially manipulate, excited state dynamics and energy transfer in molecular materials.