Hierarchically Porous and Dynamic Hydrogen-Bonded Crosslinked Organic Frameworks

About This Grant

Non-technical summary: Porous materials such as activated charcoal are essential to modern society, with critical applications in energy-efficient chemical separations, pollutant removal for clean water, and as supports for industrial catalysts. Among them, porous organic frameworks, which are carbon-based crystalline materials, stand out for their lightweight nature and precise control over nanometer-sized channels, enabling them to hold or filter molecules of different sizes. However, it remains challenging for existing materials to distinguish between molecules of similar sizes while at the same time capturing many molecules, even though such selectivity and capacity are crucial for many applications. With support from the Solid State and Materials Chemistry program in the Division of Materials Research, this project aims to overcome current limitations by developing a new family of porous organic frameworks that feature both small cavities for selectively recognizing molecules of similar sizes and larger channels for high-capacity uptake and rapid transport. These materials can expand and contract like a sponge, dynamically adjusting their large channels to enhance molecular capture and release, while maintaining the integrity of the small, selective cavities. This adaptive capability could enable more effective technologies for water and air purification, as well as energy-efficient chemical processing. The project contributes to national interests by advancing scientific knowledge and enabling materials innovations that enhance industrial efficiency. As part of the project future scientists are trained through hands-on research in chemistry and materials science. In addition, the research team engages K-12 students through outreach programs, such as “Pack Your Columns for Clean Water” and 3D-printed porous carbons, which introduce entry-level concepts in chemistry and materials science. This integration of advanced research and public education aligns with NSF’s mission to promote the progress of science and enhance national health, prosperity, and welfare. Technical Summary: Supported by the Solid State and Materials Chemistry program in the Division of Materials Research, this project focuses on the development of hierarchically porous, multifunctional hydrogen-bonded crosslinked organic frameworks (HCOFs) with tunable porosity, selective guest binding, and dynamic structural adaptability. These materials integrate macrocyclic and cage-based building blocks with novel crosslinking strategies to form single-crystalline frameworks that combine intrinsic binding sites for molecular recognition with extrinsic voids for enhanced adsorption and mass transport. The resulting HCOFs undergo highly dynamic expansion and contraction while retaining precise substrate selectivity. The first aim of the project is to construct HCOFs using rigid macrocycles and organic cages with pre-organized, chemically specific recognition sites. These building blocks enable the selective binding of similarly sized substrates, minimize network interpenetration, and promote well-controlled solid-state assembly, offering broadly applicable knowledge for the design of porous materials. The second aim introduces new crosslinking chemistries, including free-radical crosslinking, azide-alkyne cycloaddition, olefin metathesis, and photodimerizations, to reinforce structural integrity while enabling controlled network expansion and contraction. These transformations are studied in a single-crystal-to-single-crystal manner to establish clearly illustrated structure-property relationships. The third aim investigates HCOFs in their expanded states, stabilized through physical and chemical methods after solvent removal. These amorphous yet topologically preserved frameworks feature significantly enlarged channels, enabling high-capacity, selective adsorption and bridging the gap between porous frameworks and traditional polymer networks. Together, these efforts establish a new class of responsive porous organic materials with potential applications in water purification, chemical storage and separation, and industrial chemical processing. The project also integrates STEM education through outreach initiatives such as the “Pack Your Columns for Clean Water” and 3D-printed porous carbon modules, engaging K-12 students and undergraduates in hands-on learning, thereby promoting awareness of innovative materials technologies. 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.