Speaker
Description
Ultrafast pump-probe spectroscopy generally involves fluences above J/cm2. Inside a microscope with diffraction limited spots fluences can be even higher. In contrast, natural light harvesting systems operate at sun-light conditions: ~100 mw/cm2, corresponding to around 1 nJ/cm2 for typical pulsed laser, rendering conventional transient pump-probe experiments unfeasible. Here we present a novel approach StrEET - Structured Excitation Energy Transfer microscopy, combining the tracking of ultrafast transients with super-resolved spatial information, to study energy materials, such as TMDs, organic photovoltaics and especially the ultrafast dynamics and transport in light-harvesting membranes at natural light level.
Optimizing bio-inspired light-harvesting systems requires understanding how natural architectures govern energy transport. In this study, we investigate the optimal exciton diffusion in a monolayer of bacterial LH2 antenna complexes by controlling their packing density. Using novel StrEET microscopy, we track exciton diffusion at ultralow illumination conditions, below solar light level, free of any annihilation, while maintaining picosecond temporal and nanometer spatial resolution. Using fluorescence lifetime as an indicator for intermolecular coupling, we measured exciton diffusivity from the close packing to the single molecule limits. Interestingly, we observe a bell-shaped curve, where an ideal antenna concentration for optimal transport is identified. This maximum corresponds to a diffusion length close to 50 nm and a lifetime of 300 ps, consistent with Forster transport models and conditions in natural systems. Our findings show Nature’s design follows natural laws of coupling and energy transfer and provide critical design principles for the development of efficient, biologically inspired nanoscale platforms for sustainable energy conversion.