CAREER: Unraveling Excitation-Energy Transfer Processes in Excitonic Light-Harvesting Systems

在植物中发现的光收集复合体是一个复杂的分子集合，它吸收阳光并将其能量汇集到一个中心位置，在那里它被转化为可用的燃料。这种太阳能天线的效率是惊人的，它可能是自然界最壮观的分子结构之一。虽然人们对光收集复合物进行了广泛的研究，但其高效率的起源仍然是一个谜。这个问题很有挑战性。光收集复合体不仅由许多单独的分子组成，而且结构不是刚性的，分子成分是不断移动的。这种运动在促进（或阻碍）能量传输中所起的作用尚不清楚。在美国国家科学基金会化学部大分子、超分子和纳米化学项目的支持下，纽约城市学院（CCNY）的Eisele教授正在研究生物启发的纳米材料，以阐明自然？高效能源运输的秘诀。通过共同努力，Eisele教授和她的学生正在合成新的纳米结构分子组件，模仿大自然的光收集复合体的特征。然后，他们使用先进的近场扫描光学显微镜观察能量在组件中的流动，目的是了解结构波动如何影响能量传输。该项目可能会深刻影响我们对自然光合系统的理解，并可能为设计用于太阳能转换应用的高效人工系统铺平道路。此外，该项目还在包括纳米科学、光谱学和光学显微镜在内的广泛领域培养下一代科学家。通过外展活动，Eisele教授和她的学生正在与中学生和高中生合作，其中许多人来自历史上未被充分代表的少数群体，制作短片，突出纳米科学的挑战和机遇，从日常应用到超高分辨率纳米成像的最新研究。从概念上讲，为了更好地理解生物启发纳米材料中的激发能转移（EET）过程，需要模型系统能够对当前能量传输现象的理论模型进行彻底的测试。为此，Eisele教授正在合成基于单体的定义良好的模型系统，如两亲性菁菁染料和卟啉染料。在溶液中，单体自组装成超分子纳米管，显示出与自然光收集配合物相似的集体光学性质（激子）。然后将纳米管组件封装在透明（非激子）材料中，以模拟自然光收集复合物的周围蛋白质。使用近场扫描光学显微镜（NSOM）技术研究了单个纳米管的结构和光学性质，并使用飞秒泵浦探针技术跟踪了EET过程。该项目还将泵浦探测光谱与NSOM方法相结合，从而能够直接观察单个结构中的能量传输。实验结果与蒙特卡罗计算机模拟的超分子结构相辅相成。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。

The light-harvesting complex found in plants is a complex assembly of molecules that absorbs sunlight and funnels its energy to a central location where it is converted into useable fuels. The efficiency of this solar antenna is remarkable, and it is perhaps one of Nature's most spectacular molecular architectures. While the light-harvesting complex has been studied extensively, the origin of its high efficiency has remained a mystery. The problem is challenging. The light-harvesting complex not only consists of many individual molecules, but the structure is not rigid, and the molecular components are continually moving. The role that this motion plays in facilitating (or impeding) energy transport is unclear. Through support from the Macromolecular, Supramolecular and Nanochemistry Program of the NSF Division of Chemistry, Professor Eisele at The City College of New York (CCNY) is studying bio-inspired nanomaterials to elucidate Nature?s secret to efficient energy transport. Working together, Professor Eisele and her students are synthesizing new nanostructured molecular assemblies that mimic the features of the Nature's light-harvesting complex. They then watch the flow of energy through the assembly using sophisticated near-field scanning optical microscopies with the goal of understanding how structural fluctuations affect energy transport. The project could profoundly impact our understanding of natural photosynthetic systems, and could pave the way towards the design of efficient artificial systems for solar energy conversion applications. In addition, the project is training the next generation of scientists in a broad range fields including nanoscience, spectroscopy and optical microscopy. Through outreach activities, Professor Eisele and her students are working with middle- and high-school students, many from historically underrepresented minority groups, to produce short videos that highlight the challenges and opportunities of nanoscience, from everyday applications to the latest research in super-high resolution nanoimaging.Conceptually, achieving a better understanding of excitation energy transfer (EET) processes in bio-inspired nanomaterials requires model systems that allow thorough testing of current theoretical models of energy transport phenomena. To this end, Professor Eisele is synthesizing well-defined model systems based on monomers such as amphiphilic cyanine dyes and porphyrin dyes. In solution the monomers self-assemble into supramolecular nanotubes that show collective optical properties (excitons) similar to the optical properties found in natural light-harvesting complexes. The nanotube assemblies are then encapsulated in transparent (non-excitonic) materials to mimic the surrounding proteins of the natural light-harvesting complex. The structural and optical properties of individual nanotubes are studied using near field scanning optical microscopy (NSOM) techniques, and the EET process is followed using femtosecond pump-probe techniques. The project is also integrating the pump-probe spectroscopies with NSOM methods, to enable direct observation of energy transport in an individual structure. The experimental results are complemented with Monte Carlo computer simulations of the supramolecular structure.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.