Metal–organic frameworks (MOFs) are a class of crystalline, porous extended solids that are formed through coordination between metal cations and bridging organic ligands. These materials have been a topic of acute interest in the scientific community due to their intrinsic porosity, high surface area, and precise tunability. However, MOFs are typically insulating, which limits the scope of their applications. The recent development of electrically conductive MOFs has opened the door to exciting multifunctional applications in electrocatalysis, advanced electrochemical energy storage, chemical sensing, and much more. However, a molecular-level understanding of charge transport in MOFs remains lacking. My research aims to address this knowledge gap through the investigation of one-dimensional (1D) metal–organic chains. In this presentation, I will introduce the synthesis of a series of highly-tunable 1D metal–organic chains that exhibit delocalized π systems and high electrical conductivity along with studies of how structural parameters such as metal/ligand identity and chain geometry influence their overall electrical and magnetic properties. My preliminary results demonstrate trends in these structure-property relationships that may inform how these materials can be rationally designed with specific magnetic and conductive properties. Ultimately, this work will contribute towards a molecular-level understanding of charge transport and magnetism in metal–organic frameworks, enabling the design of new conductive porous materials that can use electricity to drive chemical processes.

Previous work takes inspiration from 2D metal–organic frameworks to synthesize 0D metal–organic macrocycles which maintain the conductivity of the original material while introducing solution processability. These macrocycles self-assemble into nanotubes through π-π stacking of the aromatic core but, the nanotubes do not have a preferred orientation when imaged by atomic force microscopy (AFM). We hypothesize that by adjusting solvent, drying conditions, and organic ligand functionality we can create a preferred orientation of the macrocycle nanotubes on common substrates which will improve charge carrier mobilities through the aromatic core. This work demonstrates the formation of large domains of nanotube alignment which can lead to greater charge carrier mobility. With unique ambipolar charge carrier transport, metal–organic macrocycles have applications in energy storage, chemical sensing, and electrocatalysis.

Many standard oxidants and reductants are non-reusable and toxic, so it is important to pursue cleaner alternatives. In this project, we have synthesized and characterized two metal-bipyridyl supramolecular cages and have studied their application as catalysts for the electrochemical reduction of organic substrates. Supramolecular cages are formed from the self-assembly of organic ligands and metal ions in solution, and they contain internal cavities with unique electronic microenvironments, similar to the interior of enzymes. While these polyhedral structures have been investigated as catalysts for traditional synthetic pathways, their role in electrosynthesis remains underexplored. Electrosynthesis involves the transfer of electrons to and from substrates using an applied potential, rather than chemical redox agents. This method is often hindered by a high kinetic barrier at the electrode-substrate interface, but catalysts can lower this barrier. We hypothesize that redox-active supramolecular cages – cages that can readily interconvert between charge states – can serve as effective electrocatalysts by encapsulating and transferring charge to substrates. To understand the effect of ligand geometry on electrocatalysis, I have synthesized two redox-active ligands with bipyridyl chelating groups. One contains a highly conjugated perylene core, while the other contains a compact core formed from pyromellitic dianhydride. We have metalated these ligands with iron ions to form two tetrahedral supramolecular cages. We then utilized cyclic voltammetry to assess cage-facilitated charge transfer to vicinal dihalide substrates. We observed that the reduction of multiple substrates, including 1,2-dibromo-1,2-diphenylethane, occurred at milder voltages in the presence of the cages, indicating a reduced kinetic barrier. For these substrates, we then performed bulk electrolysis, from which we determined that the percent conversion to the desired product was significantly higher when a cage was present, supporting our hypothesis. Ultimately, we aim to use these cages to enable electrosynthesis of organic feedstocks at lower voltages and with fewer byproducts.

Two-dimensional van der Waals materials are a class of materials that can be exfoliated into thin layers. Exotic properties can emerge in these thin-layer materials, such as electric polarization. In this presentation, we report the observation of irregular piezoelectric domains in natural flakes of thin-layer tungsten disulfide, a transition metal dichalcogenide (TMD), detected with piezoresponse force microscopy (PFM). These domains also exhibit different surface potential when analyzed with kelvin probe force microscopy, which is consistent with our PFM observation. We attribute the emergence of these intriguing domains to the formation of opposite R-stacked regions with inversion symmetry breaking, as opposed to inversion-symmetric H-stacked layers. To investigate this further, we performed reflectance measurements in a dual gated device with strong position dependent hysteresis, indicating different built-in potentials of the domains. Our work provides a new avenue to engineer electric polarization in thin-layer materials, which will contribute to applications such as information storage.