Structure- and Composition-Performance Relationships of Electrically Conductive Metal-Organic Frameworks, Conjugated Porous Organic Polymers, and Fused Aromatics

Abstract

Combining charge transport with permanent porosity and structural modulability, electrically conductive metal-organic frameworks (MOFs), have drawn increasing attention due to their potential use in a variety of applications including electrochemical energy storage (EES). Although fully conjugated porous organic polymers (POPs) generally exhibit lower electrical conductivities and crystallinity, they are built merely on earth abundant elements, light-weight, and thus offer great potential for EES applications. Fused aromatic materials are one of the most promising electrode materials for EES if not poorly conductive. In this thesis, the author explores structure- and/or composition-property relationships of electrically conductive MOFs, conjugated POPs, and fused aromatic materials, with the focus on their potential use in energy-related applications. Chapter 1 first introduces recent developments of electrically conductive MOFs and conjugated POPs, with particular attention paid to their structure-property relationships, and their applications as electrode materials for EES. The remaining part of Chapter 1 summarizes the use of organic electrode materials for EES, emphasizing two major obstacles. Focusing on the composition-property relationships, Chapter 2 demonstrates the continuous fine-scale tuning of band gaps over 0.4 eV and of electrical conductivity over four orders of magnitude in a series of highly crystalline binary alloys of two-dimensional electrically conducting MOFs. To probe the structure-property relationships, Chapter 3 reveals the construction of compositionally constant Ni-based MOFs and conjugated coordination polymers with different structural dimensionality, including closely π-stacked one-dimensional chains, aggregated two-dimensional layers, and a three-dimensional framework, based on 2,3,5,6-tetraamino-1,4-hydroquinone and its various oxidized forms. These compositionally constant materials exhibit distinct electronic properties caused by different dimensionality and supramolecular interactions between structural motifs. Chapter 4 presents polymeric tetraoxa[8]circulenes as a new family of porous organic polymers with light-switchable and tunable semiconducting properties. Chapter 5 and 6 focus on the use of conducting fused aromatic materials as electrodes for EES. Chapter 5 describes the design and synthesis of all-organic, fused aromatic materials that store up to 310 mAh g–1 and charge in as little as 33 seconds. This performance stems from abundant quinone/imine functionalities that decorate an extended aromatic backbone, act as redox-active sites, engage in hydrogen bonding, and enable a delocalized high-rate energy storage with stability upon cycling. Chapter 6 demonstrates that a small fused aromatic molecule whose high electrical conductivity, high capacity for redox charge storage, and complete lack of solubility in any practical solvent allow it to reversibly intercalate Li+ ions and function as a competitive cathode material for Li-ion batteries, even as a neat material.