NSF Award
1904170
Non-technical Abstract<br/><br/>Designing new porous materials is increasingly vital in enabling technological advancement and meeting societal needs ranging from clean water to next-generation batteries. Despite the necessity for structures tailored to the target application, fundamental challenges remain in preparing nanoporous materials at the same level of precision achieved in small-molecule design. A relatively new class of materials, called covalent organic frameworks, uses rigid molecular building-blocks that self-assemble into predictable, crystalline porous architectures. Planar starting molecules form two-dimensional (2D) polymer sheets that stack to give lightweight materials with uniform, nanometer-sized pores and high surface areas. While there is broad control over the individual sheet structure, there has been little advancement in controlling the stacking between layers and the corresponding material stability. This project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, aims to bridge a gap in the knowledge of covalent framework growth by controlling the interlayer structure between the 2D sheets. Trapping framework building-blocks in charged, cage-like host molecules disrupts the default interlayer stacking, allowing for the formation of modular jacketed covalent frameworks. With this award, the principle investigators and their groups study fundamental growth mechanisms for this new type of covalent organic frameworks, which expands the knowledge required to grow better next-generation materials. These new materials, both ionic and porous, are expected to accelerate advancements in separations, conductivity in electronic devices, and catalysis. This research is undertaken with a diverse group of undergraduates and masters students at Bucknell University, preparing them for future careers in the STEM fields, as well as providing opportunities to engage with the local community.<br/><br/><br/>Technical Abstract<br/><br/>This project, supported by the Solid State and Materials Chemistry program within the Division of Materials Research, explores a supramolecular approach for noncovalent functionalization of two-dimensional covalent organic frameworks (2D COFs). In the past decade, COFs have shown that controllable crystalline organic structures are readily available through self-assembly of rigid monomers via reversible linkage chemistries. Despite their potential, 2D COFs are limited by their dependence on simple interlayer sheet stacking, which prevents manipulation in the z-dimension and inhibits access to interconnected pore networks. Introducing host-guest complexation between positively charged cage molecules and planar COF monomers facilitates the design of jacketed covalent organic frameworks (J-COFs). This platform of monomer encapsulation introduces control over both material structure and functionalization through counterion selection. In this project, the synthesis and growth mechanism of J-COFs are characterized across known COF linkage chemistries, such as boronate ester, imine, and hydrazone systems. Novel solid-state properties deriving from structural incorporation of the cage species are contrasted with standard 2D COFs. This project provides undergraduate and masters students greater exposure to materials chemistry concepts, including both research opportunities as well as direct engagement with local schools and the Lewisburg Children's Museum.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
