Understanding and Controlling Reaction Mechanisms Under Vibrational Strong Coupling

在化学系化学结构、动力学和机理a （CSDM-A）项目的支持下，加州大学圣地亚哥分校的熊伟和他的团队旨在了解光学腔中一系列特定化学反应的机制。当反应物和/或生成物处于由两个部分反射镜组成的腔中，并且高度浓缩以达到所谓的强耦合状态时，腔内反应的活性和选择性可能与腔外相同的反应不同。这种现象通过简单的光学方法，为化学反应的控制开辟了一条新的途径，并将对反应工程产生深远的影响。然而，关于支持腔修饰反应的实验观察结果一直存在争议，并且腔如何修饰反应的分子水平机制仍不清楚。熊博士和他的团队旨在量化空腔中的反应，并通过光谱学了解潜在的机制。对空腔反应的正确表征和机理的理解将为合理设计修饰化学的空腔奠定坚实的基础。为了提高公众对化学的兴趣，熊博士正在YouTube上建立一个食物和化学频道，讨论食物和烹饪的基本化学。在视频中，科学家们将根据自己的背景制作食物，以拥抱我们社会的多元文化。虽然这个活动的目的之一是通过食物传播化学，这是每个人都能享受的，但另一个目的是向科学家展示现实生活中的化学。在更熟悉的环境中观察科学家，有助于激励年轻学习者追求STEM（科学、技术、工程和数学）职业，并鼓励他们的家人支持这种愿望。本项目的目的是研究由分子极性修饰的化学反应，以获得暗模式和协同性在反应中所起作用的新见解。当分子振动模式和光子腔模式的能量交换速度快于两者的寿命时，光与物质发生振动强耦合（VSC）。在VSC下，腔光子和分子振动激发杂交形成分子振动极化子。最近的报告显示了几个有趣的例子，说明在VSC条件下如何改变分子势能景观和伴随的反应途径，包括改变反应分支比和提高或抑制化学反应速率，使VSC成为一个有前途的操纵化学反应的新工具。然而，在这一新兴领域存在一些挑战。该项目通过开发一种替代的、更直接的分析方法来量化VSC下的化学，重点解决三个突出的挑战；量化反应性能和极化/暗模式动力学，以了解暗模式和极化之间的相互作用及其如何影响VSC下的化学反应；旨在了解VSC下能量传递在化学中的作用。主要研究工具包括超快光谱和GC-MS（气相色谱/质谱）等分析仪器。该项目的成果包括开发一种替代方法来量化VSC下的化学，并更好地了解VSC下的化学机制。更广泛的影响包括合理设计VSC条件的新设计原则，以控制反应并影响催化，药物分子合成，绿色化学和光化学领域。该团队还接待来自科学领域代表性不足的群体的本科生，以帮助他们熟悉研究生生活，并向他们介绍前沿研究项目，以扩大研究生研究的参与度。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。

With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Wei Xiong and his group at the University of California-San Diego aim to understand the mechanisms of a specific set of chemical reactions in optical cavities. When reactants and/or products are in a cavity composed of two partial-reflective mirrors, and are highly concentrated to reach the so-called strong coupling regime, the activity and selectivity of reactions in the cavity can differ from the same reaction outside cavities. Such a phenomenon opens a new way to control chemical reactions and can profoundly impact reaction engineering through a simple optical method. However, there has been debate about the experimental observations that support the claim of cavity-modified reactions, and the molecular-level mechanisms of how the cavities modify reactions remain unclear. Dr. Xiong and his group aim to quantify the reaction in cavities and understand the underlying mechanisms through optical spectroscopy. A proper characterization of the cavity reactions and understanding of the mechanisms will lay a solid foundation for rationally designing cavities to modify chemistry. To enhance the general public's interest in chemistry, Dr. Xiong is setting up a food and chemistry YouTube channel to discuss the basic chemistry of food and cooking. Videos will feature scientists cooking food based on their own backgrounds to embrace the diverse culture in our society. While one of the purposes of this activity is to broadcast chemistry through food, something everyone can enjoy, another purpose is to show scientists in real-life settings. Observing scientists in more familiar settings can help motivate young learners to pursue STEM (science, technology, engineering and mathematics) careers and encourage their families to support such aspirations.The goal of this project is to study chemical reactions modified by molecular polaritons to gain new insight into the roles that dark modes and cooperativity play in the reactions. Vibrational strong coupling (VSC) of light and matter occurs when molecular vibrational and photon cavity modes exchange energy faster than the lifetime of both modes. Under VSC, cavity photons and molecular vibrational excitations hybridize to form molecular vibrational polaritons. Recent reports have shown several fascinating examples of how molecular potential energy landscapes and concomitant reaction pathways can be modified under VSC conditions, including modifying reaction branching ratios and enhancing or suppressing chemical reaction rates, making VSC a promising new tool to manipulate chemical reactions. However, there are several challenges in this emerging field. This project focuses on addressing three outstanding challenges by developing an alternative and more direct analytical method to quantify chemistry under VSC; quantifying the reaction performance and polariton/dark mode dynamics to understand the interplay between dark modes and polaritons and how it influences chemistry under VSC; and aiming to understand the role of energy transfer in chemistry under VSC. The main research tools include ultrafast spectroscopy and analytical instruments such as GC-MS (gas chromatography/mass spectrometry). The outcomes of this project include the development of an alternative way to quantify chemistry under VSC and better understanding of the mechanisms of chemistry under VSC. The broader impacts include new design principles for the rational design of VSC conditions to control reactions and influence the field of catalysis, pharmaceutical molecule synthesis, green chemistry, and photochemistry. The team also hosts undergraduate research students from groups that are underrepresented in science, in order to help them become familiar with graduate life and introduce them to cutting-edge research programs in an effort to broaden participation in graduate 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.