Manipulating Exciton Superradiance Through Disorder in Supramolecular Dye Aggregates

Photosynthetic antennae and organic electronic materials use topological, structural and molecular control of delocalized excitons to enhance and direct energy transfer. Interactions between the transition dipoles of individual chromophore units allow for coherent delocalization across multiple molecular sites. This delocalization, for specific geometries, greatly enhances the transition dipole moment of the lowest-energy excitonic state relative to that of the chromophore and can greatly increase the radiative rate, a phenomenon known as superradiance. In this talk I discuss ordered, self-assembled Light Harvesting Nanotubes (LHNs) that display excitation-induced photobrightening and photodarkening. These changes in quantum yield arise due to changes in energetic disorder, which in turn increases/decreases excitonic superradiance. Through a combination of experiment and modeling, I show that intense illumination induces different types of chemical change in LHNs that reproducibly alter absorption and fluorescence properties, indicating control over excitonic delocalization. Ialso show that changes in spectral width and shift can be sensitive measures of system dimensionality, illustrating the mixed 1-2D nature of LHN excitons.