Measuring Electronic Coherence at the Single-Molecule Level with Nonlinear Coherent Spectroscopy

在化学系化学测量与成像(CMI)计划的支持下，密歇根州立大学的Elad Harel博士和他的研究小组正在开发测量单分子量子力学行为的新方法。在量子力学中，分子的行为往往取决于系统不同状态之间的微妙关系。这种被称为相干的关系很容易通过与周围环境的相互作用而被破坏，通常需要实验者在低温或高度隔离的环境中进行困难的测量，才能探索复杂系统的量子力学属性。然而，越来越清楚的是，即使在环境条件下，量子力学在分子系统的行为中也发挥着重要作用，包括将阳光转化为化学能的光合作用蛋白质。虽然已经测量了分子集合的连贯性，但了解单个分子的行为对于理解分子结构如何影响复杂系统的功能非常重要。因此，哈雷尔教授的团队正在开发工具，通过使用极其灵敏的检测方法，在单分子水平上测量一致性。该研究项目还为学生提供高级技术培训，以及针对来自一系列经济和社会背景的广泛年轻人的外联活动。单分子水平的非线性光谱学方法的发展有望揭示目前从整体方法中无法获得的重要信息。在这个项目中，哈雷尔博士和他的团队正在开发能够在室温下进行单分子非线性光谱测量的新方法。该方法使用二维电子光谱在单分子水平上探测电子相干和电子-振动耦合。这些测量揭示了复杂系统中重要的结构-功能-动力学关系，包括环境条件下的色素-蛋白质复合体和量子限制纳米晶体。了解没有非均匀展宽的真实电子相干时间及其物理起源，对于比较实验测量和理论预测，以及加深对分子相互作用的基本理解是至关重要的。研究小组正在开发的新方法有可能影响对支配广泛复杂化学体系的分子机制的理解。除了实现分子系统的重要新测量，该项目的研究目标与研究生和本科水平的学生培训紧密结合，包括研究生根据他们的研究开发为期五周的暑期辅导课程的计划。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 support from the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry, Dr. Elad Harel and his research group at Michigan State University are developing new methods to measure the quantum mechanical behavior of single molecules. In quantum mechanics, the behavior of a molecule often depends on a delicate relationship between the different states of the system. This relationship, called coherence, is easily disrupted through interactions with the surrounding environment, and often requires experimentalists to make difficult measurements at low temperatures or in highly isolated environments in order to probe the quantum mechanical properties of a complex system. However, it is becoming increasingly clear that even under ambient conditions quantum mechanics plays an important role in the behavior of molecular systems, including photosynthetic proteins that convert sunlight into chemical energy. While coherence has been measured for collections of molecules, knowing the behavior of single molecules is important for understanding how molecular structure affects the function of complex systems. Therefore, Professor Harel’s team is developing tools to measure coherence at the single-molecule level by employing extremely sensitive detection methods. The research project also provides advanced technical training for students, as well as outreach activities targeting a wide audience of young people from a range of economic and social backgrounds.The development of nonlinear spectroscopy methods at the single-molecule level holds the promise of revealing important information that is not currently available from ensemble methods. In this project, Dr. Harel and his group are developing new methods to enable single-molecule nonlinear spectroscopy measurements at room temperature. The approach uses two-dimensional electronic spectroscopy to probe electronic coherences and electronic-vibrational coupling at the single-molecule level. These measurements reveal important structure-function-dynamics relationships in complex systems, including pigment-protein complexes and quantum-confined nanocrystals under ambient conditions. Understanding the true electronic coherence time and its physical origin free of inhomogeneous broadening are critically important for comparing experimental measurements with theoretical predictions, and for developing a deeper fundamental understanding of molecular interactions. The new approach being developed by the research team has the potential to impact understanding of molecular mechanisms that govern a wide range of complex chemical systems. In addition to enabling important new measurements of molecular systems, the research goals of the project are closely integrated with student training at the graduate and undergraduate levels, including a program in which graduate students develop five-week summer tutorial courses based on their research.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.