Photo-induced charge and energy transport: from single molecules to disordered materials

我的研究兴趣集中在分子内部和分子之间的能量和电荷流动上。基本化学反应过程中的化学能和电荷流动，例如当分子改变形状或将电子转移到其邻近分子之一时。当分子系统与光相互作用时，这些过程尤其重要；在光能被吸收后，系统必须找到某种方式来“松弛”。从理论角度描述这类过程需要发展和应用处于统计力学和量子动力学交界处的模拟方法。将这些领域结合起来，对于准确捕捉从太阳能转换和化学催化到生物传感和信号传递等许多前沿问题中的这些基本化学步骤是至关重要的。这种类型的分子模拟可以帮助揭示许多能量转换问题的核心所在的潜在机制，我研究计划的最终目标是扩展和应用这些方法来研究光引发的电荷和能量传输。一般来说，研究分子系统中的电荷和能量转移问题是设计新系统的关键一步，这些新系统可以被操纵以达到预期的结果。例如，我们目前对植物和细菌等自然产生的系统如何从太阳获取和利用能量的理解，缺乏必要的细节，无法为开发能够执行类似功能的改进的合成聚光系统提供足够的一套“设计原则”。这些问题所固有的挑战是，量子系统的行为是由与其环境的相互作用决定的。这些相互作用可以跨越许多自然的时间和长度尺度，并且环境可能是无序的。分子模拟中的桥接长度和时间尺度是研究界长期存在的圣杯问题。事实上，新兴的计算基础设施在可处理的系统和过程方面继续突破边界。然而，这些计算速度远远超过了量子力学方程固有的指数标度。出于这个原因，目前需要新的动力学算法来获取相关的长度和时间尺度，例如，太阳能电池或捕光细菌中正在发挥作用的基本过程。这些对如何调整分子系统及其环境以改变其功能的见解将使人们更深入地理解如何利用分子水平的设计原则来帮助开发改进的太阳能转换材料、分子电子学和催化系统。因此，这项工作的影响将在化学、物理和材料科学的许多其他领域具有重要意义。

My research interests center on the flow of energy and electric charge in, and between, molecules. Chemical energy and electric charge flow during fundamental chemical reaction events, such as when a molecule changes shape, or transfers an electron to one of its neighbors. These processes are especially important when a molecular system interacts with light; after the light energy is absorbed the system must then find some way to “relax”. Describing these sorts of processes from a theoretical perspective requires the development and application of simulation methods that lie at the interface of statistical mechanics and quantum dynamics. Combining these areas is essential to accurately capture these fundamental chemical steps in many forefront problems ranging from solar energy conversion and chemical catalysis to biological sensing and signaling. Molecular simulations of this type can help uncover the underlying mechanisms that lie at the heart of many energy conversion problems, and the ultimate goal of my research program is to extend and apply these approaches to study light-initiated charge and energy transport. In general, studying charge and energy transfer problems in molecular systems is an essential step to engineering new systems that can be manipulated in order to achieve desired outcomes. For example, our current understanding of how naturally occurring systems, such as plants and bacteria, harvest and harness energy from the sun lacks the detail necessary to provide a sufficient set of “design principles” for the development of improved synthetic light-harvesting systems that can perform similar functions. The challenge inherent in these problems is that the behavior of the quantum system is determined by interactions with its environment. These interactions can span many natural time and length scales, and the environment can be disordered. Bridging length and time-scales in molecular simulation is a long-standing holy grail' problem in the research community. Indeed, emerging computational infrastructures continue to push the boundaries in terms of the systems and processes that can be treated. However, these computational speed-ups are far out-paced by the inherent exponential scaling of the equations of quantum mechanics. For this reason, new dynamics algorithms are currently needed in order to access the relevant length and time-scales in, for example, the fundamental processes at play in a solar cell or a light-harvesting bacterium. These insights into how molecular systems and their environments can be tuned to alter their functionality will lead to a deeper understanding of how to leverage molecular-level design principles to aid in the development of improved solar energy conversion materials, molecular electronics, and catalytic systems. Hence, the impact of this work will have importance in many other areas of chemistry, in physics, and in materials science.