Stimuli-Responsive Porous Molecular Crystals

作为该项目的一部分，Miljanic教授和他的团队在NSF固态和材料化学项目的支持下，开发和研究了被称为多孔分子晶体（PMCs）的新材料。pmc是固体晶体，让人想起海绵：它们有微小的孔，其尺寸与分子相当。在目前已知的大多数多孔材料中，孔隙在结构上是刚性的。在这些新材料中，孔隙的设计方式允许它们根据环境的变化而收缩和膨胀。具体来说，开发的材料对高压和暴露于气态化学物质有反应，包括环境污染物，如氟利昂和吸入麻醉剂。由此产生的孔径变化伴随着其光学性质的变化（即可见光和紫外光下的颜色），这种变化使其能够用于检测环境污染物。这些对压力和化学反应敏感的晶体的潜在未来应用是作为减震器、能量储存材料、传感器和可以捕获和释放有害和有用化学物质的材料。此外，该项目的社会效益还包括培养化学、材料科学和工业领域的新一代研究人员。Miljanic教授和他的同事已经成立了一家创业公司，最终可以利用这项工作中提出的多孔材料来回收麻醉剂。休斯敦大学通过持续开发能源和可持续发展的高级本科课程，并将3D打印纳入化学课程，丰富了课程内容，补充了这些努力。技术摘要：本项目由美国国家科学基金会固体与材料化学计划资助，对新型多孔材料进行了制备和研究。多孔分子晶体（PMCs）是由离散的分子组成，这些分子仅通过弱非共价相互作用在固态下结合在一起。这些连接是灵活的，可以很容易地改变pmc成分的排列。因此，预计pmc将对高压和访客进入孔隙做出反应，研究人员正在实验中验证这一点。在阿贡国家实验室，pmc结构的压力变化是通过固态核磁共振波谱、汞侵入孔隙度测定法和高压晶体学的组合来跟踪的。由于它们的荧光特性，这种孔径的变化伴随着发射性质的可见和可测量的变化。这种光学响应可用于制备甲醇和氟化制冷剂（如氟利昂、氢氟碳化物（hfc）和氢氟烯烃（hfo））的固态传感器。作为工作的最后组成部分，合成了新型多孔液晶并进行了初步研究。它们的基础是形状持久的大环，称为脱氢苯环烯，其结构可以维持柱状孔。这些具有介源基团的柱的合成装饰转化为液晶行为，这反过来又通过涉及内部和同步加速器技术的方法组合进行研究。拟议工作的更广泛影响是在有机化学和材料科学界面培训研究人员，利用pmc作为麻醉剂回收的平台，以及休斯顿大学的新课程设置，其中包括能源和可持续性课程，以及将3D打印纳入化学教学。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 AbstractAs part of this project, supported by the Solid State and Materials Chemistry program at NSF, Prof. Miljanic and his group develop and study new materials known as porous molecular crystals (PMCs). PMCs are solid crystals reminiscent of sponges: they have tiny pores, whose dimensions are comparable to those of molecules. In most currently known porous materials, pores are rigid in structure. In these new materials, pores are designed in a way which allows their shrinkage and expansion in response to changes in their environment. Specifically, the developed materials respond to high pressure and to exposure to gaseous chemicals, including environmental pollutants such as Freons and inhalation anesthetics. The resulting changes in pore dimensions are accompanied by changes in their optical properties (i.e. color under visible and ultraviolet light), and such modifications allow their use in the detection of environmental pollutants. Potential future applications of these pressure- and chemically responsive crystals are as shock absorbers, energy-storage materials, sensors, and materials that could catch-and-release chemicals-both harmful and useful ones-on demand. Additionally, societal benefits of this project include the education of a new generation of researchers at the interface of chemistry and materials science, and industry. Prof. Miljanic and coworkers have established a startup company which eventually could utilize the porous materials proposed in this work in the recycling of anesthetics. These efforts are complemented by curriculum enrichment at the University of Houston through the continued development of an upper-level undergraduate course on Energy and Sustainability, and the incorporation of 3D printing into chemistry curriculum.Technical AbstractThrough this project, supported by the Solid State and Materials Chemistry program at NSF, new classes of porous materials are prepared and studied. Porous molecular crystals (PMCs) are composed of discrete molecules which are held together in the solid state only by weak noncovalent interactions. These connections are flexible, allowing easy changes in the arrangement of PMCs constituents. As a result, it is anticipated that PMCs will be responsive to high pressures and guest entry into the pores, which the researchers are verifying experimentally. The pressure-based changes in the structures of PMCs are tracked through a combination of solid-state NMR spectroscopy, mercury intrusion porosimetry, and high-pressure crystallography at the Argonne National Laboratory. Because of their fluorescent character, such changes in pore dimensions are accompanied by visible and measurable changes in emission properties. This optical response can be used to prepare solid-state sensors for methanol and fluorinated refrigerants such as Freons, hydrofluorocarbons (HFCs), and hydrofluoroolefins (HFOs). As the final component of the work, new porous liquid crystals are synthesized and preliminarily studied. Their basis are shape-persistent macrocycles known as dehydrobenzannulenes, whose structures can sustain a columnar pore. Synthetic decoration of these columns with mesogenic groups translates into liquid crystalline behavior, which in turn is studied through a combination of methods involving both in-house and synchrotron techniques. Broader impacts of the proposed work are in the training of researchers at the interface of organic chemistry and materials science, utilization of PMCs as platforms for the recycling of anesthetics, and new curriculum offerings at the University of Houston, which include a course on Energy and Sustainability, and incorporation of 3D printing into chemistry instruction.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.