CAREER: Understanding and Ccontrolling Fatigue in Photo-Responsive MOFs: Characterizing Photochromic Transformations in Single Crystals

摘要：本项目由材料研究部固态材料化学计划资助，研究团队正在开发由紫外光激活的晶体多孔材料。光活性化学基团暴露在光线下会改变形状。这些光驱动的转变导致晶体框架的孔（孔）和通道改变形状，从而使材料能够选择性地吸收或释放客体分子，例如药物，但只有在暴露于适当波长的光下。除了促进我们对这些新材料中发生的基本光化学的理解外，该研究还建立了设计原则，以理解并最终控制和防止各种光响应材料的疲劳（失效）。教育和推广活动通过继续发展面向高年级本科生和研究生的x射线科学课程，将晶体学和x射线科学带入美国课堂。这些教育项目，包括全国范围内的水晶种植竞赛，通过为教师和学生开发动手实验和课程开发，将水晶和光的概念带入K-12教室。技术摘要：本研究的重点是识别和理解光致变色材料疲劳的根本原因，最终目标是制定控制任何光响应系统疲劳的设计原则。主要目标是对二芳基材料中的光化学进行详细的分子水平理解，二芳基材料是光响应金属有机框架的新兴领域中令人兴奋的小生境。研究的具体目的包括：(1)新型二乙烯基光开关连接剂和由这些连接剂制备的金属有机框架的合成和表征；(2)利用光谱和衍射方法量化晶体环境中光致变色分子的光物理特性，以确定反应的能量和局限性；(3)确定控制这些材料疲劳的因素和触发因素；(4)开发新技术来评估金属有机框架纳米孔内客体物质的分布，并确定它们对晶体框架光物理性质的影响；(5)利用所获得的知识合理设计和制造具有增强性能的先进光致变色材料，即提高抗疲劳性。主要研究工具包括传统和原位单晶x射线衍射（光晶体学），稳态和时间分辨吸收光谱/显微镜，核磁共振（NMR），质谱，热重分析和计算建模。

Non-technical Abstract:In this project funded by the Solid-State Materials Chemistry program of the Division of Materials Research, the research team is developing crystalline porous materials that are activated by UV light. The photo-active chemical groups change shape when exposed to light. These light-driven transformations cause the pores (holes) and channels of the crystalline frameworks to change shape leading to materials capable of selectively absorbing or releasing guest molecules, for example pharmaceutical drugs, but only when exposed to the proper wavelength of light. In addition to advancing our understanding of the fundamental photochemistry that occurs in these novel materials, the research establishes design principles to understand and ultimately control and prevent fatigue (failure) in a variety of photo-responsive materials. The education and outreach activities bring crystallography and X-ray science into U.S. classrooms through the continued development of an X-ray science course for advanced undergraduate and graduate students. The educational projects, including a nation-wide crystal growing competition, bring concepts of crystals and light to K-12 classrooms through the development of hands-on experiments and curricular development for teachers and students.Technical Abstract:This research focuses on identifying and understanding the root causes of fatigue in photochromic materials with the ultimate goal of developing design principles to control fatigue in any photo-responsive system. The primary objective is developing a detailed molecular level understanding of the photochemistry occurring within diarylethene-based materials, an exciting niche in the nascent field of photo-responsive metal-organic frameworks. Specific aims of the research include: (1) the synthesis and characterization of new diarylethene-based photoswitchable linkers and metal-organic frameworks prepared from these linkers, (2) quantifying the photophysics of photochromic molecules in crystalline environments using spectroscopic and diffraction methods to determine reaction energetics and limitations, (3) determining the factors and triggers that govern fatigue in these materials, (4) developing new techniques to assess the distribution of guest species within the metal-organic framework nanopores and determining their impact on the photophysical properties of the crystalline frameworks, (5) using the knowledge gained to rationally design and engineer advanced photochromic materials with enhanced properties, namely improved resistance to fatigue. The primary research tools include traditional and in situ single crystal X-ray diffraction (photo-crystallography), steady-state and time-resolved absorption spectroscopy/microscopy, nuclear magnetic resonance (NMR), mass spectrometry, thermogravimetric analysis, and computational modeling.