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Ultrafast Photoswitches for Reconfigurable Mixed-Dimensional Heterojunctions

Two-dimensional semiconducting materials such as MoS2 can be photosensitized with a zero-dimensional system such as CdSe quantum dots (QDs) to enhance optoelectronic properties. Upon photoexcitation of the QDs, charge transfer occurs across the mixed-dimensional heterojunction interface to the underlying MoS2 in less than one picosecond. This Northwestern University MRSEC seed project is designing and building molecules to bridge the QD-MoS2 interface, thus enabling control over this ultrafast charge transfer. These photoswitchable molecules can be rapidly toggled between two different states using different colors of light. Since this toggling also occurs on the picosecond time scale, it can dynamically reconfigure the charge transfer process, leading to quenched QD photoluminescence. These results provide a novel pathway to ultrafast control of mixed-dimensional heterojunction charge transfer.