Designing Vitrifiable Coordination Polymers and Conductive MOF Composite-based Chemiresistors Toward Advanced Functionality

Abstract

Coordination Polymers (CPs) are materials formed by the self-assembly of metal ions and organic linkers into extended, ordered networks. Among them, Metal-Organic Frameworks (MOFs) represent a prominent subclass particularly distinguished by their high intrinsic porosity. Despite the considerable versatility of these materials, their widespread application is often hindered by their crystalline powder nature, which complicates processing, and an inherent conflict between properties like high electrical conductivity and high porosity. This thesis addresses these challenges through two main research chapters. Chapter II investigates strategies to impart processability by creating hybrid glasses through distinct vitrification pathways. Chapter III focuses on designing high-performance chemiresistors by developing conductive MOF composites that reconcile the conflict between porosity and conductivity. Chapter II establishes two strategies for creating processable, purely carboxylate-based hybrid glasses. First, it details a design principle for achieving meltability by combining flexible aliphatic linkers with specific metal cations. This approach led to the synthesis of the first meltable carboxylate MOFs and their mechanically robust, water-stable melt-quenched glass. Second, the chapter explores a non-melting vitrification pathway driven by a desolvation-induced mesophase. This investigation connects the thermal behavior of these coordination networks to the principles of polymer physics, demonstrating that the vitrification pathway dictates the final mechanical properties of the hybrid glass. Chapter III focuses on the design of conductive MOF composites for chemiresistive sensing, aiming to synergistically combine conductivity and porosity. The chapter first presents a synthetic methodology for fabricating 2D conductive MOF-on-3D porous MOF core-shell architectures, addressing challenges of topological mismatch and disparate nucleation kinetics. It then elucidates the synergistic mechanisms in simpler physical mixtures, proposing a gas dependent, intercrystal charge transfer model governed by the semiconductor type of the 2D conductive MOF. This model provides a predictive tool for sensor design, and a pathway to mitigate humidity interference is also demonstrated. In summary, this thesis contributes a set of design principles and mechanistic insights that directly address key challenges in MOF-based material development. The strategies for achieving meltability and mesophase-driven vitrification provide a rational basis for designing vitrifiable CPs with tailored mechanical and chemical stability. The work also clarifies synergistic mechanisms in composites, enabling the systematic engineering of conductive MOF composite-based chemiresistors with enhanced sensing performance. Taken together, these findings provide validated pathways to transform traditional CPs into materials possessing the advanced functionality required for their application in processable glasses, structural components, and high performance electronic devices.