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

在这项由化学系化学结构、动力学和机制-B计划资助的项目中，鲍灵格林州立大学化学系的马尔科姆·D·E·福布斯教授正在研究自由基的结构、变化(动力学)和反应活性。自由基是一种短暂的、活性很强的物种，由暴露在热或光下的稳定分子发生裂解而产生。自由基的特征是没有配对的电子，而大多数稳定的分子处于最低能量状态，其所有电子都是配对的。使用一种称为时间分辨电子顺磁共振的专门光谱技术，可以在短时间尺度上在有组织的结构中观察到自由基，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。这些结果加深了对纠缠自旋态的理解，纠缠自旋态在量子计算、量子传感和量子信息系统中具有潜在的应用前景。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)以及光催化和药物输送等领域。福布斯的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一项针对高中生的暑期研究项目。自旋波函数演化和分子运动在光谱学方法中密切相关，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，例如自旋关联自由基对的纳米反应模型。该项目的一个主要目的是将化学诱导电子自旋极化的自由基-三重态对机制(RTPM)建立在更坚实的理论基础上，从而使其更有助于在纳米尺度上理解受限空间中分子运动的本质。在均相和非均相体系中使用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相遇的次数，从而提供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、超精细耦合)，提供了有关极性和粘度的信息，特别是旋转迁移率。在TREPR谱中，由于偶极相互作用的调制引起的快速电子自旋弛豫，激发的三重态是静默的，该团队利用了这一优势。最后，实验期间既没有消耗三重态前体，也没有消耗氮氧化物。这一裁决反映了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。

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.