Effects of Surface Ligation on Charge Extraction from Wurtzite Cadmium Selenide Quantum Platelets and Quantum Belts
Date of Award
Doctor of Philosophy (PhD)
This dissertation presents the synthesis of flat, colloidal wurtzite CdSe quantum platelets and quantum belts for ligand exchange to novel and existing organic and inorganic L-, X-, and Z- type ligands. Use of these ligands in conjunction with the semiconductor nanocrystals allows for examination of their ligand exchange abilities, photoluminescence quenching efficiencies, and charge transfer properties.
First, zinc and cadmium dithiocarbamate compounds [M(S2CNR1R2)2] are used as ligands on wurtzite CdSe quantum belts. Complete ligand exchange is achieved when the belts are initially ligated with Cd(oleate)2, a Z-type ligand, prior to the exchange, as opposed to n-octylamine or ammonia, which are both L-type ligands. Spectroscopic data, experimentally determined lattice strains, and ligand exchanges with [Na][Et2CNS2] and [NH4][MePhNCS2] establish that the [M(S2CNR1R2)2] ligands bind as bound-ion-pair X-type ligands with (S2CNR1R2)- groups ligated directly to the quantum belt surfaces and [M(S2CNR1R2)]+ groups acting as counter-cations to balance the charge. The bound-ion pair X-type dithiocarbamate ligands do not impart any special electronic effects to the CdSe quantum belts.
Second, methyl viologen (MV2+), and the L-type amino-derivative ligands, MV2+(CH2)nNH2 (n = 2, 4, and 6), are used for ligand exchange reactions on wurtzite CdSe quantum platelets and quantum belts. The photoluminescence of both the quantum platelets and quantum belts is fully quenched after partial ligand exchange to MV2+ and MV2+(CH2)nNH2. Spectroscopic and compositional data establish that this initial-ligand substitution occurs only on the thin edge facets of the quantum platelets and quantum belts, while the top and bottom facets remain ligated by oleylamine. Analysis of the quenching data reveal that the MV2+(CH2)nNH2 ligands are more- efficient photoluminescence quenchers than MV2+. Differences in the time-dependent transient- absorption spectra of the MV2+(CH2)nNH2-exchanged quantum platelets and quantum belts show that electron transfer occurs preferentially on the polar, short-edge facets of the nanocrystals.
Last, the X-type carboxylate-methyl viologen derivative ligands [MV2+(CH2)nCO2–] Br–I– [NH4+] (n = 2, 4, and 6) are used for ligand exchange reactions on CdSe quantum platelets and quantum belts. The same experiments used in the L-type amino-methyl viologen experiment are conducted and the results with the X-type ligands are compared to those of the L-type ligands. Initial ligand substitution to quench the photoluminescence of the nanocrystals still occurs only on the thin edges of the quantum platelets and quantum belts. However, the X-type carboxylate- methyl viologen ligands are more-efficient quenchers than the L-type amino-methyl viologen ligands due to their preference for polar facets. Transient-absorption data establishes that electron transfer still occurs preferentially on the polar, short-edge facets of the nanocrystals.
Chair and Committee
William E. Buhro
Richard A. Loomis, Bryce Sadtler, Kade Head-Marsden, Erik Henriksen,
Meyer, Hailey, "Effects of Surface Ligation on Charge Extraction from Wurtzite Cadmium Selenide Quantum Platelets and Quantum Belts" (2022). Arts & Sciences Electronic Theses and Dissertations. 2804.
Available for download on Friday, June 02, 2023