CAREER: Designing Elastic Hydrogen-bonded Crosslinked Porous Organic Materials

Non-technical abstract Porous organic frameworks are carbon-based, light-weight crystalline materials with defined nano-sized pores. Such materials are promising for applications in molecular and energy storage, environmental remediation, as well as separation of important chemical intermediates and products. The key challenge associated with the development of porous organic frameworks is the tradeoff between high crystallinity for selective molecular adsorption and separation, and high chemical stability for long-term usage. With joint support from the Solid State and Materials Chemistry program in the Division of Materials Research and the Established Program to Stimulate Competitive Research (EPSCoR), this CAREER project addresses this challenge and develops a new family of highly ordered, chemically stable, and elastic porous organic materials. Through a new synthesis approach elasticity becomes a feature of porous organic frameworks, allowing them to dynamically expand their structure by breaking hydrogen bonds, and recover to their original crystalline form by reforming the temporary bonds. These elastic materials are expected to achieve high adsorption capacity and selectivity over the existing porous organic materials. Furthermore, incorporating active species into these materials enables next-generation environmental and energy-related applications to advance national prosperity. Through the integrated education and outreach activities Prof. Ke and his research group make abstract scientific concepts more accessible to students at all levels as well as the general public, and show how material science can address global problems. Specifically, this is done by (1) designing an interactive demonstration named "Traveling Through Nano Space" to illustrate fundamental concepts related to porous materials, (2) mentoring high-school and undergraduate students to develop an easy-to-replicate 3D printer and materials; and (3) developing an active-learning class to engage students, especially those from underrepresented groups, in their STEM education. Technical Abstract With this CAREER project, jointly supported by the Solid State and Materials Chemistry program in the Division of Materials Research and the Established Program to Stimulate Competitive Research (EPSCoR), the next-generation of elastic porous organic materials are designed and synthesized. In particular, this class of materials has high crystallinity, allowing for precise structure-property analysis and endowing them with high chemical stability for applications such as chemical storage, separation and potentially catalysis. A series of hydrogen-bonded crosslinked organic framework (HCOF) materials are constructed through the combination of hydrogen bond directed assembly and photo-crosslinking in single crystals. The project provides an in-depth understanding of the structure-property relationship of HCOF materials by focusing on three aspects: First, the crystal structures of HCOFs and their molecular precursors can reveal atomic-level structural information that are difficult to obtain in conventional porous organic frameworks. Second, integration of flexible crosslinkers provides HCOFs with unique elasticity, which enables them to dynamically adjust their 3D architecture by breaking and reforming hydrogen bonds, thereby increasing the guest binding capacity and selectivity based on different substrate-framework interactions. Third, decreasing the degree of crosslinking in HCOFs provides a range of partially crosslinked frameworks with greater elasticity and novel nanoscale morphologies, which are not accessible using the synthetic strategies of traditional porous organic frameworks. This approach also enables HCOFs to incorporate catalytically active moieties that are not compatible with traditional organic framework materials, supporting next-generation environmental and energy-related applications. The research efforts enrich the educational and outreach activities of this project, which aim to make abstract scientific concepts more accessible to students at all levels as well as the general public. This is achieved by (1) designing an interactive demonstration named "Traveling Through Nano Space" to illustrate fundamental concepts related to porous materials, (2) mentoring high-school and undergraduate students to develop an easy-to-replicate 3D printer and materials; and (3) developing an active-learning class to engage students, especially those from underrepresented groups, in their STEM education. 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.