Quantum Dots as Redox Photocatalysts for Organic Synthesis – PhotoRedoQs

Alkoxyl radicals are well-known species that possess a truly unique reactivity. However, due to the lack of efficient and mild methods to generated them, their rich chemistry is underutilized in synthesis. We propose to investigate the use and optimization of classical QD as photocatalysts to develop several innovative methods to generate alkoxyl (and other) radicals.

In order to enhance QD-photocatalyst quantum efficiency, the grafting of Ag-nanoparticules (Ag-NP)) and Au-nanoparticles (Au-NP) to the QDs will be examined. This modification is expected to favor the charge separation step after light absorption by the QD by electron transfer to the Ag-NP. Furthermore, this will enhance the reactivity of holes that stay in the QD after charge separation by delaying their recombination with electron lying in the Ag-NP. At this stage of the project we already obtained a reliable synthesis for the nanocompistes The photocatalytic behavior of this new class of QDs will be tested with more established synthetic transformation such as the generation of radicals via oxidative decarboxylation of carboxylic acids and oxidation tertiary amines.

Due to the coronavirus crisis, we are still working on the first half of the project. It is too soon to propose future prospects.

Later

In the last decade, the emergence of photoredox catalysis has revolutionized the field of synthetic organic chemistry. Catalyst design has been boosted by development of catalysts for solar energy conversion. Ruthenium and iridium coordination complexes are playing a major role in this development. Besides these homogeneous catalysts, the use of heterogenous semiconductor photoredox catalysts for synthesis is still in his infancy. We propose here a research program dedicated to the investigation of semiconductor colloidal quantum dots (QDs) as photoredox catalysts for synthetic organic chemistry. These nanocrystalline catalysts are highly attractive since they combine some of the advantages of the homogeneous catalysts, such as large extinction coefficient in the visible spectrum, and retain the ability to be removed by ultra-filtration or centrifugation. Moreover, QDs are very resistant to
photobleaching and their redox properties may be fine-tuned by changing their composition (CdS, CdSe, ZnO, ZnSe), controlling their size and modifying the ligands used to stabilize them. Finally, finding substitutes to the costly ruthenium and particularly iridium catalysts, will open new perspective for industrial application of photoredox catalysis.
The project is divided in two closely related topics: 1) the use of QD-photocatalysts to generate alkoxyl radicals; 2) the development of a new class of photocatalysts combining QDs and Ag nanoparticles (QD-Ag).
1) Generation of alkoxyl radicals using QD-photocatalysts. Alkoxyl radicals are well-known species that possess a truly unique reactivity. However, due to the lack of efficient and mild methods to generated them, their rich chemistry is underutilized in synthesis. We propose to investigate the use and optimization of classical QDs as photocatalysts to develop several innovative methods to generate alkoxyl radicals. For instance, the oxidation of
stable and easily prepared borate complexes will be examined.
2) Development of QD-Ag composite catalysts. In order to enhance QD-photocatalyst quantum efficiency, the grafting of Ag-nanoparticles (Ag-NPs) to the QDs will be examined. This modification is expected to favor the charge separation step after light absorption by the QD by electron transfer to the Ag-NP. Furthermore, this will enhance the reactivity of holes that stay in the QD after charge separation by delaying their recombination with electrons lying in the Ag-NP. The photocatalytic behavior of this new class of QDs will be tested with more established synthetic transformations such as the generation of radicals via oxidative decarboxylation of carboxylic acids and oxidation of tertiary amines.