CAREER: Ultrafast Nanoscopy of Energy Transport in Molecular Assemblies

美国国家科学基金会化学部的化学结构、动力学和机理A部分(CSDMA)项目支持普渡大学的黄立白教授开发创新的显微技术，提供分子吸收的光能如何在空间和时间移动的电影。这项研究中的分子强烈地吸收光，可能对太阳能电池等设备有用。为了在太阳能转换设备中使用它们，分子必须紧密堆积在一起，而堆积对能量从一个分子转移到另一个分子的方式有很大影响。这些因素决定了太阳能电池的效率。通过跟踪能量在不同堆积的分子组件中的运动方式，这项工作正在解决控制能量迁移速度和距离的机制，并为高效收集太阳能的结构设计提供指导。为了实现这些目标，人们正在开发显微镜技术，以100飞秒(一飞秒是千分之一秒)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为演示，以说明量子力学中的关键概念。这些示范的写作作业被用来促进对抽象概念的高级认知理解。研究人员还在开发一项科学推广计划，将最先进的太阳能研究带到印第安纳州西北部的高中。本项目中开发的超快纳米方法直接成像激子在多个长度和时间尺度上的传输，以阐明分子组装中相干和非相干的能量转移路径。同时绘制了100fs时间分辨率和~20 nm空间精度的激子布居和光激发动力学图。这些测量首次提供了相干传输的空间范围的可视化。利用两个模型分子聚集体系统地研究了中间耦合区域中的能量传递。线性H聚集体作为一维激子模型量子线，有望实现长程波状相干输运。管状聚集体被用来阐明激子传输作为维度的函数。在模型系统结果的基础上，通过调节分子间的短程和长程耦合，实现了控制超分子组装中传输的长期目标。研究和教育活动相结合，以培养下一代K-12、本科生和研究生级别的太阳能研究人员。

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.