Designing Quantum Dot Interfaces for Photoredox Catalysis

Abstract

Chemical manufacturing accounts for 10% of total global energy consumption and 7% of greenhouse emissions. Thermodynamically uphill reactions may be driven by photoredox catalysts under ambient conditions, converting solar to chemical energy. Semiconductor quantum dots (QDs) are efficient photoredox catalysts due to their high absorptivity and easily tuneable redox potentials. They are routinely used in the hydrogen evolution reaction, but there remains much to be understood when applying QDs to organic synthesis. In this work, we present several strategies to synthesise more active QD photocatalysts for organic reactions via modulation of the semiconductor interface. In the first chapter, we explore catalyst speciation under reaction conditions and elucidate a mechanism for unwanted reactions happening at the catalyst surface that affect its stability. In the second chapter, we make more stable and active catalysts via ligand shell engineering using charge transfer mediators. In the third chapter, we use infrared (IR) spectroscopy to measure relative binding energies of common aliphatic ligands on nanocluster surfaces, which appear to be more labile than previously thought. Lastly in chapter four, we make anisotropic heterostructures with long-lived excited states and study their optoelectronic properties and charge transfer rates to molecular acceptors. This work increases our atomistic understanding of mechanisms involved in QD organic photoredox catalysis and provides design principles for making stable and more active catalysts.