Charge Transporting Supramolecular pi-Donor/Acceptor Arrays Based on Redox-Active Metallacycles, Metal-Organic Cages, and Daisy-Chain Coordination Polymers

在化学系大分子、超分子和纳米化学（MSN）项目的支持下，克莱姆森大学的Sourav Saha将开发导电和光捕获超分子组件，该组件由精确组织的电子供体和受体单元组成，限制在超分子容器中。电子供体和受体芳香分子含有共轭pi-系统，当它们像一副纸牌一样共面pi堆叠时，允许电子通过共振和空间通过键离域。此外，电活性芳香分子经常吸收和发射光，从而显示出迷人的光学性质。当富电子（pi-供体）和缺电子（pi-受体）pi-系统以交替的方式组织时，由于通过电荷转移甚至部分电子转移相互作用，从供体到受体单元的电子容易通过空间离域，它们传导电流的能力进一步增强。在克莱姆森大学的萨哈小组进行的这项研究中，重复的电子供体和受体单元将通过封装在专门设计的超分子容器中而堆叠起来。容器将使用铂金属离子和有机连接物来精确控制其尺寸以及电子和光学特性。因此，它们将容纳不同大小的pi-供体和受体单位，以调节它们的三维顺序和方向。这项工作产生的结果可能会导致新的半导体、晶体管、光收集系统、电致变色和热致变色材料。萨哈博士将致力于培训和指导不同群体的本科生和研究生，通过克莱姆森大学的EUREKA！并通过“做一天研究生”计划，为佐治亚南方大学（Georgia Southern University）的少数族裔学生提供职业指导和动力，让他们继续接受研究生教育。此外，将在贝克学院中学和罗珀山科学博物馆开展当地推广项目，以吸引K-12学生，鼓励他们考虑在STEM（科学、技术、工程和数学）领域接受高等教育。本研究将重点研究使用氧化还原活性多组分金属环、金属有机笼和菊花链配位聚合物作为超分子容器，将氧化还原互补的客体pi系统封装在其腔内的鲁棒超分子pi-供体/受体阵列的合成、组装和结构-功能关系研究。由两个平行氧化还原活性面和由异聚铂角连接的可变长度正交连接体组成的三组分矩形金属环和四方棱柱金属环将被用作封装氧化还原互补客体的超分子容器。容器和它们的客体包合物将协调连接以组装雏菊链聚合物。重点将放在通过系统地改变宿主的腔尺寸和宿主和客体的氧化还原特性来控制离散pi-供体/受体堆栈的形成。包合物的结构和组成将使用一套晶体学、光谱学和电子显微镜技术来确定。将进行系统的研究，以检查主客体和客体客体电荷转移和电子转移相互作用如何影响所得到的包合物的颜色、发射、带隙和电荷传输能力。如果这项工作成功，将开发一种新的自下而上的策略，使用氧化还原活性超分子容器组装强大的超分子pi-供体/受体堆栈，并为其作为超分子导线、半导体和光收集材料在未来的电子和光伏器件中的应用铺平道路。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。

With the support from the Macromolecular, Supramolecular, and Nanochemistry (MSN) program in the Division of Chemistry, Sourav Saha of Clemson University will be developing charge-conducting and light-harvesting supramolecular assemblies consisting of precisely organized electron donor and acceptor units confined to supramolecular containers. Electron donor and acceptor aromatic molecules contain conjugated pi-systems that allow electron delocalization through bonds via resonance as well as through space when they are cofacially pi-stacked like a deck of cards. In addition, electroactive aromatic molecules often absorb and emit light, thereby displaying fascinating optical properties. When electron rich (pi-donors) and deficient (pi-acceptor) pi-systems are organized in an alternating fashion, their ability to conduct electrical current is further accentuated due to facile through-space electron delocalization from the donor to the acceptor units via charge-transfer and even partial electron transfer interactions. In this research conducted by the Saha group at Clemson, repeating electron donor and acceptor units will be stacked by encapsulating them within specifically designed supramolecular containers. The containers will be constructed using platinum metal ions and organic linkers to precisely control their dimensions and electronic and optical properties. As such, they will accommodate pi-donor and acceptor units of different sizes to regulate their three-dimensional ordering and orientation. The results generated by this work can potentially to lead to new class of semiconductors, transistors, light-harvesting systems, and electrochromic and thermochromic materials. Dr. Saha will work to train and mentor diverse groups of undergraduate and graduate students, provide research experience to high school seniors through Clemson’s EUREKA! program, and offer career guidance and motivation to largely minority students from Georgia Southern University to pursue graduate education through a ‘Be a Grad Student for a Day’ initiative. In addition, local outreach programs at Beck Academy Middle School and Roper Mountain Science Museum will be conducted to engage K-12 students and encourage them to consider pursuing higher education in STEM (science, technology, engineering and mathematics) fields.This research will focus on the synthesis, assembly, and structure–function relationship studies of robust supramolecular pi-donor/acceptors arrays using redox-active multicomponent metallacycles, metal-organic cages, and daisy chain coordination polymers as supramolecular containers that can encapsulate redox-complementary guest pi-systems inside their cavities. Tricomponent rectangular metallacycles and tetragonal prismatic metallacages consisting of two parallel redox-active faces and orthogonal linkers with variable lengths connected by heteroligated platinum corners will be employed as supramolecular containers to encapsulate redox-complementary guests. The containers and their guest-inclusion complexes will be coordinatively linked to assemble daisy-chain polymers. Emphasis will be placed on controlling the formation of discrete pi-donor/acceptor stacks through systematic variations of the cavity size of the hosts and the redox properties of the hosts and guests. The structures and compositions of inclusion complexes will be determined using a suite of crystallographic, spectroscopic, and electron microscopic techniques. Systematic studies will be conducted to examine how the host/guest and guest/guest charge-transfer and electron-transfer interactions will influence the color, emission, bandgaps, and charge transport capability of the resulting inclusion complexes. This work, if successful, will develop a novel bottom-up strategy to assemble robust supramolecular pi-donor/acceptor stacks using redox-active supramolecular containers and pave way to their applications as supramolecular wires, semiconductors, and light-harvesting materials in future electronic and photovoltaic devices.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.