Probing Charge Transport Mechanisms in 2D Semiconductive Metal Organic Frameworks
Abstract
Metal organic frameworks (MOFs) are a class of highly porous crystalline materials constructed from metal nodes connected by multitopic organic ligands. Due to their unique properties such as large surface area, tunable pore structure, and structural diversity, they have demonstrated potential in a wide array of applications including gas storage and separation, sensing, catalysis, and drug delivery. However, there are only a handful of MOFs reported that have electrical conductivity, which prevents their applications in photoelectronic and photocatalytic applications. This is because hard metals and redox inactive ligands with terminal hard linking bases such as carboxylates are often used in constructing these materials. In addition, the porous nature of these materials leaves voids between the polymeric chains, which cuts off communication between the densely packed units. It was not until recently that MOFs with charge conductivity were reported after replacing the hard-linking nodes with soft acid/base counterparts. However, the charge transport mechanism that is responsible for their conductivity remains poorly understood. The objective of my research projects is to have a fundamental understanding of charge transport mechanisms in MOFs to facilitate their applications in photo-electronics and photocatalysis. In this report, I will discuss fundamental insights into charge transport mechanisms in 2D M-THQ MOFs (M= Cu, Fe, Ni, and Zn) (chapters 3 and 4) and 1D pyrene-tetra thiol-based nanosheets (chapter 6). Chapter 3 focuses on the experimental evidence of through bond charge transport in Cu-THQ semiconductive MOF through a combination of spectroscopic techniques and DFT calculation. Chapter 4 reports the dependence of exciton dynamics and band structure engineering on metal nodes in M-THQ MOF (M= Fe, Ni, and Zn). Chapter 5 discusses the impact of Ligand size in 2D MOFs on photoconduction and charge transport mechanisms. In Chapter 6 I discuss the design and synthesis of 1D pyrene-tetra thiol-based MOFs, and the impact of pi-pi stacking on photoconduction. I also synthesized a new sulfur-decorated MOF for potential application in metal ion batteries and white light emissive COFs which will be discussed in chapters 7 and 8. Finally, chapter 9 outlines the future directions of this project.