Surface Access Gating by Excited States (SAGE) for Quantum Dot Photocatalysis

The objective of this research is to understand and control the excited state surface chemistry of colloidal nanocrystals being targeted as light absorbers and catalysts in artificial photosynthetic molecular constructs. The surface chemistry of molecules known as ligands bonded to nanocrystal surfaces mediate the primary energy and electron transfer processes that underpin photochemical and photocatalytic transformations in artificial photosynthetic reactions. Such ligand layers on nanocrystals have dual and often competing roles of facilitating surface access of catalysts and charge acceptor species involved in photocatalytic processes while providing chemical stability and protecting the nanocrystal surfaces from photodegradation. The research plan is framed around the hypothesis that it is possible to design nanocrystal/ligand interactions that enhance the change in ligand bonding in the excited states of nanocrystals to create more permeable ligand shells just when they are needed – when the nanocrystals are in their excited states and ready to drive photocatalytic processes. Then, when the nanocrystals return to their ground states, the ligand surface bonding strength can be restored to protect nanocrystals until the next photoexcitation event, the result of the process described as the Surface Access Gating by Excited states (SAGE) effect. The research plan seeks to uncover design rules about how to control the SAGE effect and to reveal mechanisms by which the molecular and material components of nanocrystalline photocatalytic systems can be integrated to utilize the effect to facilitate the primary light harvesting, charge transferring, and chemical bond forming components of photocatalytic systems. The research plan will establish that the SAGE effect offers the unexpected opportunity to accomplish both the synergistic coordination of the primary molecular dynamics and charge transfer processes in photocatalysis while at the same time enhancing the durability of nanocrystals in these reactions.