(Invited) Ultrafast Studies of Self-Assembled Biomimetic Materials, Metal-Organic-Frameworks, and Plasmonic Metamaterials for Solar Light Harvesting

Abstract

Ultrafast photoprocesses can play important roles in light harvesting, such as picosecond excitonic hopping between chromophores, or femtosecond decays of hot (nonthermal) carriers in plasmonic metamaterials following photoexcitation. In this talk, I focus on ultrafast photoprocesses in nanostructured materials of interest for light harvesting. In particular, ultrafast light harvesting processes in three types of materials are described. I describe the design of new biomimetic nanostructures for light harvesting involving the use of chromophore-doped peptide amphiphiles to create varied and potentially self-healing structures for transporting energy. Through environmental controls, unique opportunities for tuning the structural shape of the self-assembled materials are possible, thereby altering the resultant energy transport properties. The dependence of excitonic transport on chromophore concentration is described. The second topic is that of exploring light harvesting in metal-organic-frameworks using porphyrin building blocks. Efforts to characterize the degree of anisotropy (directionality) in exciton flow as well as distance of exciton migration are described. Finally, I describe the study of plasmonic metamaterials, where nanostructuring and the creation of “gap-plasmons” dramatically increases the number of hot carriers produced under illumination. Our efforts to spectroscopically characterize the production and decay of hot carriers with variations in size, shape, and composition are shown. Physical insights into how to extract the hot carriers before loss of energy to thermalization is given. This work was performed, in part, at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, and supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.