Time-resolved exciton delocalization from transient absorption spectroscopy

The temporal evolution of exciton delocalization in aggregates determines the excitons’ dynamics. Although the equilibrium exciton delocalization length can be measured through several well-established methods, capturing its temporal dynamics remains challenging. Here, we present an experimental approach to quantifying the time-dependent evolution of exciton delocalization in aggregates through transient absorption spectroscopy. Our method employs excited-state absorption and stimulated emission to probe the exciton delocalization while utilizing ground-state absorption to track and filter out the evolution of exciton concentration through a ratio-based analysis. Through experimental validations and theoretical simulations, we demonstrate that this approach quantitatively captures the temporal evolution of exciton delocalization while remaining insensitive to concurrent competing dynamics, such as exciton-exciton annihilation. Furthermore, this methodology could be extended to measure the time-resolved quantum Fisher information in molecular aggregate systems.