CAREER: Ultrafast Nanoscopy of Energy Transport in Molecular Assemblies

NSF化学部的化学结构，动力学和机制A部分（CSDMA）计划支持普渡大学的黄立白教授开发创新的显微镜技术，提供分子吸收的光能如何在空间和时间中移动的“电影”。 这项研究中的分子强烈吸收光，并可能用于太阳能电池等设备。 为了在太阳能转换装置中使用它们，分子必须紧密地堆积在一起，并且堆积极大地影响能量如何从一个分子转移到另一个分子。这些因素决定了太阳能电池的效率。 通过跟踪能量如何在具有不同包装的分子组装体中移动，这项工作正在解决控制能量迁移速度和距离的机制，并为设计有效的太阳能收集结构提供指导。 为了实现这些目标，正在开发显微镜技术，以100飞秒（飞秒是一秒的千万亿分之一）的分辨率记录快速能量转移事件，并以20纳米（一纳米是十亿分之一米）的分辨率成像能量迁移距离。 黄博士正在开发一种新的教学模式，将主动学习与科学写作相结合，旨在更好地教授物理化学中的抽象概念。特别是，该奖项中的太阳能应用正在发展成为演示，以说明量子力学中的关键概念。 这些演示的写作作业被用来促进抽象概念的高层次认知理解。 研究人员还在制定一项科学推广计划，将最先进的太阳能研究带到印第安纳州西北部的高中。 在这个项目中开发的超快纳米显微镜方法直接成像激子传输跨越多个长度和时间尺度，以阐明分子组装中的相干和非相干能量转移途径。 激子的人口和动力学光激发被映射与同时100 fs的时间分辨率和~20 nm的空间精度。这些测量提供了第一种可视化的相干传输的空间范围。两个模型分子聚集体被用来系统地探测能量转移的中间耦合制度。线性H聚集体作为模型1D激子量子线，其中预期的长程波相干传输。管状聚集体被用来阐明激子输运作为一个功能的维度。在模型系统结果的基础上，通过调节短程和长程分子间耦合来实现控制超分子组装体传输的长期目标。 研究和教育活动相结合，以教育下一代太阳能研究人员在K-12，本科和研究生水平。

The Chemical Structure, Dynamics and Mechanisms Part A (CSDMA) Program in the Chemistry Division of the NSF supports Professor Libai Huang at Purdue University to develop innovative microscopy techniques that provide 'movies' of how light energy absorbed by molecules moves in space and in time. The molecules in this research absorb light strongly and are potentially useful for devices such as solar cells. In order to use them in solar energy conversion devices, the molecules have to be closely packed together and the packing greatly influences how energy is transferred from one molecule to the other. These factors determine the efficiency of the solar cell. By tracking how energy moves in molecular assemblies with different packing, this work is resolving mechanisms that control the speed and distance of energy migration and providing guidelines for designing structures for efficient solar energy harvesting. To achieve these goals, microscopy techniques are being developed to record fast energy transfer events with a resolution of 100 femtoseconds (a femtosecond is one quadrillionth of a second) and to image energy migration distance with a resolution of 20 nanometers (a nanometer is one billionth of a meter). Dr. Huang is developing a new instructional model that integrates active learning with scientific writing aimed at better teaching abstract concepts in physical chemistry. In particular, solar energy applications in this award are being developed into demonstrations to illustrate key concepts in quantum mechanics. Writing assignments of these demonstrations are being utilized to promote high-level cognitive understanding of abstract concepts. The researchers are also developing a scientific outreach program to bring state-of-the-art solar energy research to high schools in Northwest Indiana. The ultrafast nanoscopy methods being developed in this project directly image exciton transport across multiple length and time scales to elucidate coherent and incoherent energy transfer pathways in molecular assemblies. Exciton populations and dynamics following photoexcitation are being mapped with simultaneous 100 fs temporal resolution and ~20 nm spatial precision. These measurements provide first-of-a-kind visualization of the spatial extent of coherent transport. Two model molecular aggregates are employed to systematically probe energy transfer in the intermediate coupling regimes. Linear H aggregates serve as model 1D excitonic quantum wires in which long-range wavelike coherent transport is expected. Tubular aggregates are employed to elucidate exciton transport as a function of dimensionality. Building on results from the model systems, the long-term goal of controlling transport in supramolecular assemblies is achieved by modulating both short- and long-range intermolecular coupling. The research and educational activities are integrated to educate the next generation of solar energy researchers at the K-12, undergraduate, and graduate levels.