CAREER: Designing Elastic Hydrogen-bonded Crosslinked Porous Organic Materials

多孔有机框架是一种碳基轻质晶体材料，具有明确的纳米级孔。这类材料在分子和能量存储、环境修复以及重要化学中间体和产品的分离等方面具有广阔的应用前景。开发多孔有机框架的关键挑战是在选择性分子吸附和分离的高结晶度和长期使用的高化学稳定性之间进行权衡。在材料研究部固态与材料化学项目和促进竞争研究的既定计划（EPSCoR）的共同支持下，CAREER项目解决了这一挑战，并开发了一种新的高度有序、化学稳定、有弹性的多孔有机材料。通过一种新的合成方法，弹性成为多孔有机骨架的一个特征，允许它们通过破坏氢键来动态扩展其结构，并通过重组临时键来恢复其原始晶体形态。这些弹性材料有望比现有的多孔有机材料具有更高的吸附能力和选择性。此外，将活性物种纳入这些材料中，使下一代环境和能源相关应用能够促进国家繁荣。柯教授和他的研究小组透过综合教育和外展活动，让不同层次的学生和公众更容易接触抽象的科学概念，并展示材料科学如何解决全球问题。具体来说，这是通过(1)设计一个名为“穿越纳米空间”的交互式演示来说明与多孔材料相关的基本概念，(2)指导高中生和本科生开发易于复制的3D打印机和材料；(3)开设主动学习班，让学生，特别是那些来自代表性不足群体的学生参与STEM教育。本CAREER项目由材料研究部固态与材料化学项目和促进竞争研究的既定计划（EPSCoR）共同支持，设计和合成了下一代弹性多孔有机材料。特别是，这类材料具有高结晶度，允许精确的结构-性质分析，并赋予它们高的化学稳定性，用于化学储存，分离和潜在的催化等应用。通过单晶氢键定向组装和光交联相结合，构建了一系列氢键交联有机骨架材料。本项目重点从三个方面深入了解HCOF材料的结构-性能关系：第一，HCOF及其分子前体的晶体结构可以揭示常规多孔有机骨架难以获得的原子级结构信息。其次，柔性交联剂的集成为HCOFs提供了独特的弹性，使其能够通过破坏和重组氢键来动态调整其三维结构，从而提高基于不同底物-框架相互作用的客体结合能力和选择性。第三，降低HCOFs的交联程度，提供了一系列具有更大弹性和新颖纳米级形态的部分交联框架，这是传统多孔有机框架的合成策略所无法获得的。这种方法还使HCOFs能够加入与传统有机框架材料不兼容的催化活性部分，支持下一代环境和能源相关应用。这些研究工作丰富了该项目的教育和推广活动，其目的是使各级学生和公众更容易理解抽象的科学概念。这是通过(1)设计一个名为“穿越纳米空间”的交互式演示来实现的，以说明与多孔材料相关的基本概念，(2)指导高中生和本科生开发易于复制的3D打印机和材料；(3)开设主动学习班，让学生，特别是那些来自代表性不足群体的学生参与STEM教育。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstractPorous 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 AbstractWith 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.