QLC: EAGER: Quantum control of energy transfer pathways and chemical reactions

化学中的挑战之一是利用光从化学反应中产生特定的产物。如果这一目标能够实现，将推动一系列广泛的技术，从能源转换（例如，光到电或合成燃料）到化学传感，到化学过程效率的一般改进。 在这个由化学系化学结构、动力学和机理项目支持的项目中，密歇根州立大学的Marcos Dantus和Benjamin Levine教授正在使用实验和理论建模相结合的方法来设计可以导致特定化学反应的激光脉冲。 光脉冲的持续时间通常为几飞秒（飞秒是一秒的千万亿分之一），并且可以被设计（“成形”）以包含所需范围的光波长（颜色范围），甚至在脉冲持续时间内改变波长。 根据它们的形状，光脉冲以不同的方式影响分子内电子的运动。 由于电子在分子的原子之间形成键，因此可以控制键如何断裂和重新形成。 换句话说，激光脉冲的形状可以控制化学反应的结果。参与该项目的研究生和本科生学习光物质相互作用，并与从不同角度考虑这些现象的团体（光谱学家、理论家和合成化学家）合作。研究人员定期将高中生纳入他们的研究工作，并与旨在增加追求研究生学习和研究事业的代表性不足的学生数量的计划密切合作。该项目实施了一种新的策略，用于实现凝聚相中大有机分子的能量流和反应性的连贯控制。认识到不同的电子激发态经历不同的化学反应，整形激光脉冲被用于（a）填充具有期望反应性的电子态，以及（B）最小化从期望电子态自发跃迁（例如，内部转换）的概率。为了实现（B），量子控制策略从半经典（驱动振动波包沿着特定的反应坐标）到没有经典类似物的量子策略都被使用。例如，可以利用电子态之间交叉点附近的拓扑效应来影响反应结果和强耦合，例如当势能面被光场修饰时。 在这种情况下，自然能量流被改变，分子系统？可以增强与驱动场的相干性。先进的量子动力学模拟能够确定初始波包结构与反应结果之间的因果关系，从而为后续实验提供信息。内转换的成功控制通过来自更高激发态的荧光产率来跟踪。随后，类似的策略被用于驱动一系列染料中的解离反应，这些染料仅在被激发到更高的激发态时才释放出高效的荧光团。总之，这一结合实验和理论的努力是阐明战略，以最大限度地提高所需的光子能量驱动凝聚相化学反应的分数。这一奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

One of the challenges in chemistry is to produce specific products from chemical reactions using light. If this objective can be achieved, a wide range of technologies would be advanced, from energy conversion (e.g., light to electricity or synthetic fuel) to chemical sensing, to general improvement of chemical process efficiency. In this project supported by the Chemical Structure, Dynamics and Mechanisms-A Program of the Division of Chemistry, Professors Marcos Dantus and Benjamin Levine of Michigan State University are using a combination of experiment and theoretical modeling to design laser light pulses that can result in specific chemical reactions. The light pulses are typically a few femtoseconds in duration (a femtosecond is one-quadrillionth of a second), and can be designed ("shaped") to contain a desired range of light wavelengths (a range of colors), or even change wavelength over the pulse duration. Depending on their shape, the light pulses affect the motions of electrons inside the molecules in different ways. Since electrons form the bonds between the atoms of a molecule, it is possible to control how the bonds break and re-form. In other words, the shape of the laser light pulses can control the outcome of chemical reactions. The graduate and undergraduate students involved in this project learn about light-matter interactions and collaborate with groups that consider these phenomena from different perspectives (spectroscopists theorists, and synthetic chemists). The researchers regularly include high school students in their research efforts and work closely with programs aimed at increasing the number of underrepresented students who pursue graduate study and research careers.This project implements a novel strategy for achieving coherent control of the energy flow and reactivity of large organic molecules in the condensed phase. Recognizing that different electronic excited states undergo different chemical reactions, shaped laser pulses are being used to (a) populate electronic states with desirable reactivities, and (b) minimize the probability of spontaneous transition out of the desired electronic state (e.g. internal conversion). In pursuit of (b), quantum control strategies that range from semi-classical (driving the vibrational wave packet along a particular reaction coordinate) to quantum strategies with no classical analogue are being used.For example, topological effects near intersections between electronic states can be exploited to influence the reaction outcome and strong coupling, for example when potential energy surfaces are dressed by the light field. In such cases, the natural energy flow is altered and the molecular system?s coherence with the driving field can be enhanced. Advanced quantum dynamical simulations are enabling the determination of causal relationship between the structure of the initial wave packet and reaction outcomes, thus informing subsequent experiments. Successful control of internal conversion are tracked by the fluorescence yield from higher excited states. Subsequently, similar strategies are used to drive dissociative reactions in a series of dyes, which release a highly efficient fluorophore only when excited to a higher excited state. Together, this combined experimental and theoretical effort is elucidating strategies to maximize the fraction of photon energy needed to drive a condensed phase chemical reaction.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.