Using Amphiphilic Semiconducting Polymers to Control Structure and Exited State Dynamic in Conjugated Organic Assemblies

化学系的大分子、超分子和纳米化学项目凭借这一奖项支持加州大学洛杉矶分校(UCLA)的Sarah H.Tolbert教授和她的团队开发高效利用光能的人工光合作用系统。从这项研究中获得的理解可能会使未来生产廉价的太阳能电池或制造利用阳光进行重要化学反应的设备。在植物的光合作用中，落在植物叶片上的光线会以一种特定的方式激发电子，启动一系列化学反应，植物利用该反应序列还原地捕获二氧化碳(CO2)，并将二氧化碳部分转化为葡萄糖的碳原子。该项目使用相同的想法来创建各种人工光合作用系统，以有效地从可见光中获取和利用能量。人工光合作用的基本问题是，即使利用光来激发电子的能量相对容易，但很难保持所需的状态；电子经常在没有执行有用的化学操作的情况下返回到其原始起点。这项工作使用了特殊设计的分子系统，这些系统在水中自组装成预定的结构。这些结构控制电子在被光激发后的运动，以确保达到所需的化学状态。除了潜在的科学进步，这个多学科项目还为国家需要的领域的本科生和研究生提供培训。该项目还有助于将从阳光和纳米材料中收集能量的相关主题的实验带到洛杉矶地区的高中。托尔伯特教授的团队正在研究具有内在各向异性、最小的电荷复合和高吸光率的有机系统的组装。该项目是研究人员之间的三方合作，他们在合成适当的分子(Yves Rubin-UCLA)、了解这些分子系统的结构和自组装(Sarah Tolbert-UCLA)以及监测这些组装的光动力学和光化学(Benjamin Schwartz-UCLA)方面拥有互补的专业知识。在生物光合作用系统中，光的吸收导致了必要的电荷分离状态，具有近100%的量子产率，这要归功于电子转移级联的进化调节，该级联在空间上分离电荷，防止复合。该项目研究了具有固有各向异性的类似人造有机组件的创建，这些组件旨在最大限度地减少电荷复合，同时优化光吸收。这项工作的一个具体目标是合成一大类两亲性半导体给电子体和两亲性小分子电子受体，它们在水溶液中自发形成柱状胶束。这些分子具有一系列的大小、电荷、电子结构和空间约束，使它们能够根据特定的疏水和空间相互作用以可预测的方式自组装。下一个目标是从结构和光学上表征组件，以了解所创建的几何图形。最终目标是用光谱学和功能光电子设备研究组件，以确定哪些设计变化可以进一步提高电荷分离的效率。总体而言，这些关于自组装聚光聚合物的设计和调节的研究有望为人工光合作用系统的发展做出贡献。从长远来看，通过这些基础研究取得的进展有望为光伏和光催化领域提供有用的知识和见解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With this award, the Macromolecular, Supramolecular, and Nanochemistry Program in the Chemistry Division is supporting Professor Sarah H. Tolbert and her team at the University of California, Los Angeles (UCLA) to develop artificial photosynthesis systems to efficiently use light energy. The understanding gained from this research may allow the future production of inexpensive solar cells or the fabrication of devices that use sunlight to perform important chemical reactions. In photosynthesis in plants, light falling on a plant leaf causes an electron to be excited in a specific fashion, launching a chemical reaction sequence that the plant utilizes to capture carbon dioxide (CO2) reductively and convert CO2-moieties into the carbon atoms of the glucose. This project uses the same ideas to create a variety of artificial photosynthesis systems to efficiently harvest and utilize energy from visible light. The basic problem with artificial photosynthesis is that even though it is relatively easy to use light to energetically excite an electron, it is difficult to maintain the required state; electrons often return to their original starting point without performing useful chemistry. This work uses specially designed molecular systems that self-assemble into predetermined structures in water. Those structures control the motion of electrons after they are photo-excited to ensure that the desired chemical state is achieved. In addition to the potential scientific advances, this multidisciplinary project provides training for undergraduate and graduate students in areas of national need. The project also helps bring experiments on related topics of energy harvesting from sunlight and nanoscale materials to Los Angeles area high schools.Professor Tolbert’s team is examining the assembly of organic systems with intrinsic anisotropy, minimized charge recombination, and high light absorption. The project is a three-way collaboration among researchers who have complementary expertise in synthesizing the appropriate molecules (Yves Rubin - UCLA), in understanding the structure and self-assembly of these molecular systems (Sarah Tolbert - UCLA), and in monitoring the photodynamics and photochemistry of these assemblies (Benjamin Schwartz-UCLA). In biological photosynthetic systems, absorption of light leads to the requisite charge-separated state with nearly 100% quantum yield, thanks to evolutionary tuning of electron transfer cascades that spatially separate charges, preventing recombination. This project examines the creation of analogous artificial organic assemblies with intrinsic anisotropy, that are designed to minimize charge recombination while optimizing light absorption. One specific aim of this work is to synthesize a large family of amphiphilic electron-donating semiconducting polymers and amphiphilic small-molecule electron-acceptors that spontaneously form cylindrical micelles in aqueous solution. These molecules are made with a range of sizes, charges, electronic structures, and steric constraints, allowing them to self-assemble in a predictable manner according to specific hydrophobic and steric interactions. The next aim is to characterize the assemblies structurally and optically to understand the geometries that are created. The final aim is to study the assemblies spectroscopically and in functional opto-electronic devices to determine what design changes can further enhance the efficiency of charge-separation. Overall, these studies on the design and tuning of self-assembling light-harvesting polymers are expected to contribute to the development of artificial photosynthetic systems. In the longer term, advancements made through these foundational studies are expected to provide useful knowledge and insight for the fields of photovoltaics and photocatalysis.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.