Sulfur Reduction by 1,2-Aminothiols and Spectroscopic Tools for Studying Nanocrystal Surfaces

This dissertation reports three separate projects during my time at the University of Notre Dame. Chapter 1 reviews the research conducted on the reduction, oxidation, and electrostatics of nanocrystals (NCs) surfaces, highlighting their impact on electronic properties. The emphasis is placed on reviewing the spectroscopic, electrochemical, and computational techniques employed to investigate the redox-active surface sites and trap states. Chapter 2 describes research with nucleophilic 1,2-aminothiol compounds that reduce elemental sulfur to form polysulfides in both aqueous and nonpolar organic solvents. By monitoring the formation of these polysulfides, we show the hydrogen-bonding group of the amine with the closest proximity results in the most rapid reduction of elemental sulfur. We then apply the knowledge gained from studying these interactions between aminothiols, and elemental sulfur to facilitate the transfer elemental sulfur to alkenes with the aid of these aminothiol compounds. Chapter 3 describes the study of the surfaces of cesium lead halide perovskite nanocrystals (CsPbX3 NCs) through the utilization of trimethylsilyl trifluoromethanesulfonate (Me3SiOTf) for the quantitative and irreversible silylation of anionic ligands in OA-- and oleylamine-capped CsPbBr3 and CsPbCl3 NCs. Employing NMR and FTIR spectroscopies alongside elemental analysis, the study demonstrates the distinct reactivity of Me3SiOTf with CsPbBr3 and CsPbCl3 NCs. In the case of CsPbBr3 NCs, Me3SiOTf reacts by removing a weakly bound ligand population from the surface while revealing an inert, strongly bound ligand population. This treatment induces surface anion exchange for trifluoromethanesulfonate resulting in enhanced photoluminescence quantum yields. For CsPbCl3 NCs, Me3SiOTf abstracts chlorides resulting in the destabilization of the NC lattice. We account this difference in reactivity by the Si–Cl bond being stronger than the Si–Br bond which results in Me3SiOTf abstracting all the chlorides from the NC. Chapter 4 describes efforts to probe CdSe NCs surface dipole and facets. We show the development of a [CdFe(CO)4] probe that is sensitive to changes in the surface dipole. We show evidence that [CdFe(CO)4] probe preferentially binds to the (111) facet. These results demonstrate the probe can be utilized to track changes to the (111) facet.