Date of Award
Winter 2025
Project Type
Dissertation
Program or Major
Biochemistry
Degree Name
Doctor of Philosophy
First Advisor
Krisztina Varga
Second Advisor
Rick Cote
Third Advisor
Feixia Chu
Abstract
Nanomaterials are increasingly integrating into our daily lives, as evidenced by their use in common products ranging from nanomedicine to optical devices. However, there remains a knowledge gap regarding the molecular behavior of ligands on the surface of nanocrystals, as well as how the interactions between molecules and nanocrystals influence the resulting properties of the nanocrystals. The aim of this study was to provide further insights to address that gap of knowledge by investigating various synthesis and environmental conditions that modulate the properties of the semiconducting nanomaterial, i.e., quantum dots. Chapter 1 will provide a brief background on quantum dots (QDs), including their properties and applications. This chapter also includes an introduction to circular dichroism spectroscopy, the primary technique used to measure chiroptical properties in this research. Finally, the chapter introduces the chirality of QDs, focusing on the proposed origins of ligand-induced chirality and the factors that modulate this phenomenon. In Chapter 2, the synthesis of ligand-functionalized cadmium sulfide (CdS) QDs was studied using various polar solvents and different ammonium countercations. The results demonstrated that both the solvents and the countercations significantly modulated the chirality transfer from the ligands to the QDs. Specifically, the more nonpolar tetrabutylammonium hydroxide (TBAOH) base proved most versatile, enabling not only greater yield and success in the synthesis of chiral QDs in polar solvents but also the first successful synthesis of chiral QDs in the nonpolar cyclohexane solvent. Chapter 3 investigated the influence of the capping ligand’s ionic form on the surface binding geometry of L-threonine functionalized CdS QDs (L-Thr-CdS QDs), a factor that ultimately controls their resulting optical and chiroptical properties. The ligand’s ionic form was modulated by varying the concentration of the base TBAOH. The TBAOH base exhibited a dual role beyond merely facilitating ligand solubility during phase transfer ligand exchange. The presence of excess achiral OH– anions appeared to compete for QD surface binding sites, thereby influencing the chiroptical properties. Crucially, the post-synthetic reversibility of these chiroptical states was demonstrated through simple acid-base titrations. Furthermore, time-dependent studies revealed a spontaneous, self-correction mechanism of the QD-ligand system, where unstable initial binding geometries rearranged over time to achieve the thermodynamically favored chiroptical state. Chapter 4 was an investigation of the use of apple juice and red wine, both complex natural mixtures, for their ability to induce predictable chiroptical properties in CdS and cadmium selenide (CdSe) QDs. The chiral profiles for the juice- and wine-functionalized QDs were found to be substantially similar to those of QDs functionalized with neat L-malic acid (L-MA) and L-tartaric acid (L-TA), respectively. This similarity allowed for the identification of L-MA (in apple juice) and L-TA (in red wine) as the principal chiral inducers of the QDs among the diverse mixture of chiral and achiral compounds in the surrounding medium. These results highlighted the potential of QDs to selectively report chiral molecules in complex mixtures without requiring elaborate chiral recognition reporting systems. This research provided a comprehensive investigation into controlling the chiroptical and electronic properties of semiconductor nanocrystals, specifically QDs, through precise modulation of their surface chemistry and environment. These findings provide further fundamental understanding of how molecule-nanocrystal interactions induce specific optical and chiroptical properties, which will aid the rational design and synthesis of tailorable nanomaterials.
Recommended Citation
Kwon, Yu Ri, "Dynamic and Solution-Phase Control of Ligand Induced Chirality in Colloidal Quantum Dots" (2025). Doctoral Dissertations. 2976.
https://scholars.unh.edu/dissertation/2976