This dissertation describes investigations into the two primary mechanisms by which the optical bandgap of colloidal quantum dots (QDs) may be post-synthetically modified: (i) by the quantum-confined Stark effect and (ii) by exciton-delocalizing surface capping ligands. This work demonstrates that through the use of ligand-exchange strategies that enable either of these two mechanisms, the optical bandgap of the QDs is responsive to changes in the pH or the potential of the solution phase environment. This work has applications to the fields of photocatalysis, where surface-specific interactions at the QD interface are poorly understood, as well as the field of biosensing, where ultrafast probes of dynamic biological processes have yet to be achieved. The first chapter of this dissertation describes the background required to approach the rest of the work herein, the second chapter of this dissertation describes the use of a weakly-interacting ligand to promote quasi-reversible optical bandgap modification as a function of pH in aqueous solution, the third chapter describes the use of N-heterocyclic carbenes (NHCs) as exciton-delocalizing ligands that electronically couple to the excitonic wavefunction of the QD with a magnitude dependent on the NHC backbone substituents, the fourth chapter describes the optical response of the QD bandgap to reduction of a redox sensitive NHC ligand, and the fifth chapter summarizes the work presented herein and outlines future directions for this area of study. These studies are carried out using a variety of physical and chemical techniques but rely in particular on ground state absorbance and emission spectroscopy, nuclear magnetic resonance spectroscopy, x-ray photoelectron spectroscopy, and electrochemistry. The research compiled in this dissertation provides the basis for future investigations of the dynamic modification of the QD bandgap to the bulk solution environment, with the ultimate goal of developing ultrafast optical sensors for the detection of photocatalytic steps and biological processes.

Creator

• Westmoreland, Dana Emily

DOI

• https://doi.org/10.21985/n2-cp7b-hj79

Subject

• Chemistry

Language

• en

Alternate Identifier

• etdadmin_upload_748612
• http://dissertations.umi.com/northwestern:15158

Keyword

• Quantum dots
• ligands
• interfaces

Date created

• 2020-01-01

Resource type

• Dissertation

Rights statement

• In Copyright