Mapping the Evolution of Spatial Exciton Coherence through Time-Resolved Fluorescence.

Quantum coherence is expected to have a positive effect on the transfer efficiency of excitation energy through photosynthetic aggregates and conjugated polymers, but its significance to the functioning of these molecular assemblies remains largely unknown. We propose a new experimental means to monitor the coherence between distant molecular sites on a time scale relevant to energy transfer. Through numerical calculations, we demonstrate that the range of such spatial coherence continually scales as the 0-0 to 0-1 vibronic peak ratio in time-resolved fluorescence spectroscopy. As such, this observable allows one to monitor the coherent evolution of an excited state, displaying the large coherence length following optical excitation, and the subsequent dephasing over time.