This talk focuses on the use of semiconductor nanoparticles or quantum dots (QDs) as the sole photocatalyst for photoinduced electron transfer (PET) reactions and the optimization of their surface, ligands, and structure to increase their viability as charge transfer catalysts. QDs have typically acted as sensitizers for separate, molecular or metal co-catalyst which restricts reactions to selected co-catalyst binding sites and sacrifices the high surface area native to these nanomaterials. Direct electron transfer from the QD, however, is limited as many reactions require multiple electrons transferred to a single substrate. We demonstrate that using phosphate ligands leads to “bare” QDs with underpassivated Cd(2+) atoms which can be reduced to form Cd(0) sites. These reduced surface states facilitate two-electron transfer reactions such as aldehyde or proton reduction while maintaining a high density of catalytic sites on the QD surface. We go on to investigate how QDs can act as the sole catalyst for underexplored reactions such as light-mediated polymerization. Specifically, we show that QDs can mediate reversible addition-fragmentation chain transfer (RAFT) polymerization with living polymerization kinetics and high propagation efficiency. As polymerization only occurs with illumination, the reaction provides temporal resolution of polymer growth and a method for the synthesis of precise block copolymers as monomers can be replaced in the dark. Finally, we demonstrate that the nanoparticles can be easily removed which facilitates polymer purification and catalyst recycling, unlike molecular catalysts.

Optimization of the surface, ligands, and structure of semiconductor nanocrystal quantum dots (QDs) for photocatalytic charge transfer reactions

2019 Spring National Meeting

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