Probes, Labels, Traps, and Reporters: Exploring the Modern Spin Chemistry Landscape

在这个由化学部化学结构、动力学和机理b项目资助的项目中，鲍灵格林州立大学化学系的Malcolm D. E. Forbes教授正在研究自由基的结构、变化（动力学）和反应性。自由基是一种寿命短、反应性强的物质，是由稳定的分子暴露在热或光下破碎而产生的。自由基的特征是具有未配对的电子，而大多数处于最低能量状态的稳定分子的特征是所有电子都是成对的。使用一种称为时间分辨电子顺磁共振的专门光谱技术，自由基可以在短时间尺度上观察到有组织的结构，如囊泡（生物细胞模拟物）、胶束（水中的油滴）、气泡、聚合物基质和其他超分子结构，如有机纳米晶体。这些结果提供了对纠缠自旋态的更深入理解，在量子计算、量子传感和量子信息系统中有潜在的应用。这项工作的科学影响涉及医学、量子计算（控制高度纠缠的电子自旋系统）、涂层（薄膜固化和干燥）、光催化和药物输送等领域。福布斯实验室积极参与图书馆和博物馆的公共宣传活动。他们参加了俄亥俄州西北部高中生的暑期研究项目。自旋波函数演化与分子运动密切相关的光谱方法，特别是时间分辨电子顺磁共振（TREPR）。它们的动力学可以通过使用理论模型来分析，例如自旋相关自由基对的纳米反应器模型。该项目的一个主要推力是将化学诱导的电子自旋极化的自由基-三重态对机制（RTPM）置于更强大的理论基础之上，并使其更有助于理解纳米尺度上密闭空间中分子运动的本质。在均相和非均相系统中使用RTPM自旋极化进行分子动力学实验研究的优点包括，在氮氧化物中观察到的电子自旋极化的大小直接取决于它与光激发三重态的接触次数，从而提供了定量的平移扩散信息。该团队还研究了氮氧化物自旋报告器的线形（强度、线宽、超细耦合），给出了极性和粘度的信息，特别是旋转迁移率。激发态的三重态在TREPR光谱中是沉默的，这是由于对偶极相互作用的调制引起的快速电子自旋弛豫，该团队利用了这一优势。最后，在实验过程中，三重态前体和氮氧化物都不被消耗。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。

In this project, funded by the Chemical Structure, Dynamics, and Mechanisms-B Program of the Chemistry Division, Professor Malcolm D. E. Forbes of the Department of Chemistry at Bowling Green State University is investigating the structure, changes (dynamics), and reactivity of free radicals. Free radicals are short-lived, very reactive species resulting from the fragmentation of stable molecules which have been exposed to heat or light. Free radicals are characterized by having unpaired electrons, in contrast to most stable molecules in their lowest energy state, which have all of their electrons paired. Using a specialized spectroscopic technique called time-resolved electron paramagnetic resonance, free radicals can be observed on short time scales in organized structures such as vesicles (biological cell mimics), micelles (oil droplets in water), bubbles, polymer matrices, and other supramolecular structures such as organic nanocrystals. The results provide a deeper understanding of entangled spin states, which have potential use in quantum computing, quantum sensing, and quantum information systems. The scientific impact of the work reaches the fields of medicine, quantum computing (control of highly entangled electron spin systems), coatings (thin film curing and drying), and photocatalysis and drug delivery. The Forbes' laboratory is active in public outreach to libraries and museums. They participate in a summer research program for high school students in Northwest Ohio.Spin wave function evolution and molecular motion are intimately connected in spectroscopic methods, especially time-resolved electron paramagnetic resonance (TREPR). Their dynamics can be analyzed through the use of theoretical models such as the nano-reactor model for spin-correlated radical pairs. A major thrust of the project is to place the radical-triplet pair mechanism (RTPM) of chemically induced electron spin polarization on a stronger theoretical footing, and in doing so make it more useful for understanding the nature of molecular motion in confined spaces on the nanoscale. The advantages in using RTPM spin polarization for experimental studies of molecular dynamics in both homogeneous and heterogeneous systems include the magnitude of the electron spin polarization observed in the nitroxide is directly dependent on the number of encounters it experiences with the photoexcited triplet state, providing quantitative translational diffusion information. The team also investigates the line shape of the nitroxide spin reporter (intensities, line widths, hyperfine couplings) gives information about polarity and viscosity, in particular rotational mobility. The excited triplet state is silent in the TREPR spectrum because of fast electron spin relaxation, induced by modulation of the dipolar interaction and this advantages is exploited by the team. Finally, neither the triplet precursor or the nitroxide are consumed during the experiment.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.