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将开发电荷传导和捕光超分子组件，这些组件由精确组织的电子供体和受体单元组成，局限于超分子容器中。电子给体和受体芳族分子含有共轭π系统，当它们像一副纸牌一样共面π堆叠时，该共轭π系统允许电子经由共振通过键以及通过空间离域。此外，电活性芳香族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（π-供体）和缺电子（π-受体）π-系统以交替方式组织时，它们传导电流的能力由于经由电荷转移和甚至部分电子转移相互作用从供体到受体单元的容易的通过空间电子离域而进一步增强。在克莱姆森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将它们封装在专门设计的超分子容器中来堆叠。这些容器将使用铂金属离子和有机连接剂来构建，以精确控制它们的尺寸以及电子和光学特性。因此，它们将容纳不同尺寸的π-供体和受体单元，以调节它们的三维有序和取向。这项工作产生的结果可能会导致新的半导体，晶体管，捕光系统，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，提供研究经验，高中毕业生通过克莱姆森的尤里卡！该计划，并提供职业指导和动力，主要是少数民族学生从格鲁吉亚南方大学追求研究生教育，通过“是一个格拉德学生一天”的倡议。此外，还将在贝克学院中学和罗珀山区科学博物馆开展当地外展计划，以吸引K-12学生，并鼓励他们考虑接受STEM高等教育（科学，技术，工程和数学）领域。这项研究将集中在合成，组装，以及使用氧化还原活性多组分金属杂环，金属有机笼，和菊花链配位聚合物作为超分子容器，其可以将氧化还原互补客体π-体系包封在它们的空腔内。由两个平行的氧化还原活性面和通过异配铂角连接的长度可变的正交连接体组成的三组分矩形金属环和四方棱柱金属笼将用作超分子容器来封装氧化还原互补客体。容器和它们的客体包合物将配位连接以组装菊花链聚合物。重点将放在控制离散的π-供体/受体堆栈的形成，通过系统的变化的空腔大小的主机和主机和客人的氧化还原性能。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，以检查如何主机/客户和客户/客户的电荷转移和电子转移相互作用将影响的颜色，发射，带隙，和电荷传输能力的包合物。这项工作，如果成功的话，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π-供体/受体堆叠，并为它们作为超分子导线，半导体，和光-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进行评估，更广泛的影响审查标准。

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.