Guest-Induced Electrical Conductivity and Photovoltaic Activity of Metal-Organic Frameworks

非技术摘要：以清洁、安全和可持续的方式推进现代技术的前景取决于不断的创新和新功能材料的供应，这些材料可以产生和储存能量，并执行无数其他复杂的功能。由金属离子簇和有机连接体自组装而成的结晶多孔材料（称为金属-有机框架（MOFs））表现出显著的合成简单性、结构多样性和尺寸选择性的客体吸收能力，这使它们成为各种先进应用的有吸引力的平台。虽然它们的实际应用是有据可查的，但电子和光子MOFs仍处于起步阶段，发展迅速。该项目由美国国家科学基金会的固态和材料化学计划支持，重点是开发刺激响应型MOFs，不仅可以在其空腔内捕获互补的客体分子，还可以使它们参与特定的电子相互作用，以刺激新的特性和功能，特别是电荷传导和光到电能的转换。在功能化电极上生长的电活性和光活性MOFs的精确取向的膜被集成到原型装置中，以利用填充有互补客体的预组织的多孔结构来促进电和光伏装置中的定向电荷移动。系统的结构-性质关系研究展示了刺激响应型MOFs如何适应不同的物理和化学输入，以及如何利用其可调的电子和光学性质。除了为研究生和博士后研究人员提供一个前沿的研究和学习环境外，这个跨学科项目还使PI能够吸引本科生和高中生参与研究，通过在当地学校和科学博物馆开展外展活动，激励年轻一代追求科学和技术方面的高等教育，并在公众论坛上讨论科学突破，提高公众对基础研究重要性的认识。技术摘要：导电性和光伏活性是金属有机框架最令人垂涎但最遥远的特性之一。然而，缺乏固有的电荷载流子密度和捕光能力，剥夺了许多现有的多孔框架的可调的电子和光学特性，这些特性是它们作为可行的半导体和光伏材料的能力的关键。为了解决这些问题并将MOFs转化为可行的电子和光子材料，在这个项目中，PI和他的团队（1）基于氧化还原和光敏配体构建刺激响应MOFs，这些配体可以与各种客人，施加的电场和光相互作用并响应，以创造新的非天然特性，（2）生长健壮，在功能化电极表面上以自下而上的方式取向的MOF膜，其可以促进定向电荷移动，和（3）用互补的氧化还原掺杂这些刺激响应性MOF膜，活性客体，其可以通过与配体相互作用产生移动的电荷载流子，并通过形成延伸的叠层而促进电荷分散通过骨架。在客人渗透之前和之后以及在存在和不存在光的情况下测量的MOF膜的电流-电压曲线揭示了它们的刺激响应性质以及封装的电活性客人对它们的电子和光学性质的影响。由于客体插层是一个普遍存在的非破坏性过程，它可以被广泛地用于在任何自适应MOFs中设计非本征电学和光子行为。PI实验室开发的基于MOF的太阳能电池原型也用于外展活动，向K-12学生展示光能到电能的转换，并激励他们追求科学，技术，工程和数学方面的高等教育。该奖项反映了NSF的法定使命，并通过使用基金会的智力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 Abstract:The prospect of advancing modern technologies in a clean, safe, and sustainable way depends on constant innovation and supply of new functional materials that can produce and store energy and perform myriad other complex functions. Self-assembled from metal ion clusters and organic linkers, crystalline porous materials known as metal-organic frameworks (MOFs) exhibit remarkable synthetic simplicity, structural diversity, and size-selective guest uptake capacity, which make them attractive platforms for a variety of advanced applications. Although their practical applications are well documented, electronic and photonic MOFs are still at their infancy and evolving rapidly. Supported by the Solid State and Materials Chemistry program of the National Science Foundation, this project focuses on developing stimuli-responsive MOFs that not only capture complementary guest molecules inside their cavities, but also engage them in specific electronic interactions to stimulate new properties and functions, particularly, charge conduction and light to electrical energy conversion. Precisely oriented films of electro- and photoactive MOFs grown on functionalized electrodes are integrated into prototype devices to exploit the preorganized porous architectures filled with complementary guests to promote directional charge movement in electrical and photovolatic devices. Systematic structure-property relationship studies demonstrate how stimuli-responsive MOFs adapt to different physical and chemical inputs and how their tunable electronic and optical properties can be exploited. In addition to providing graduate students and postdoctoral researchers a cutting-edge research and learning environment, this interdisciplinary project is enabling the PI to engage undergraduate and high school students in research, motivate younger generation to pursue higher education in science and technology through outreach activities at local schools and science museum, and raise the public awareness on the importance of basic research by discussing scientific breakthroughs in public forums. Technical Abstract:The electrical conductivity and photovoltaic activity are among the most coveted but remote properties of metal-organic frameworks. The lack of intrinsic charge carrier density and the light-harvesting capability, however, deprives many existing porous frameworks of tunable electronic and optical properties that are key to their abilities to serve as viable semiconductors and photovoltaic materials. To address these issues and transform MOFs into viable electronic and photonic materials, in this project, the PI and his team are (1) constructing stimuli-responsive MOFs based on redox- and photoactive ligands that can interact with and respond to various guests, applied electric field, and light to create new non-native properties, (2) growing robust, oriented MOF-films in a bottom-up fashion on functionalized electrode surfaces that can promote directional charge movement, and (3) doping these stimuli-responsive MOF films with complementary redox-active guests that can produce mobile charge carriers by interacting with the ligands and facilitate charge dispersion through the frameworks by forming extended ð-stacks. The current-voltage profiles of MOF films measured before and after guest infiltration and in the presence and absence of light reveal their stimuli-responsive nature and the impact of the encapsulated electroactive guests on their electronic and optical properties. Since guest intercalation is a ubiquitous and non-destructive process, it can be adopted broadly to engineer non-native electrical and photonic behaviors in any adaptive MOFs. The prototype MOF-based solar cells developed in the PI's lab are also used for outreach activities to demonstrate light to electrical energy conversion to K-12 students and motivate them to pursue higher education in science, technology, engineering, and math.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.