Toward High Intensity Forbidden EPR Transitions In Bimetallic Complexes

在化学系化学结构、动力学和机理B项目的支持下，科罗拉多州立大学化学系的Joseph Zadrozny教授正在开发新型双核过渡金属配合物，以探测禁止电子顺磁共振（EPR）光谱跃迁。本研究的目的是利用这些双核物种的特征来了解分子结构如何帮助违反EPR选择规则以实现高强度转变。正在探索的特定转换可能会产生使用EPR转换的生物成像技术的新功能。该研究项目跨越无机化学和物理化学的界面，合成和光谱分析是工作的关键部分。该计划更广泛的推广目标将是为合成化学家创建一个易于访问的课程，以接近EPR的选择规则。该计划将遵循通常用于更常见技术的教学策略，例如紫外-可见光谱学，因此旨在成为将新化学家带入EPR领域的基石。这项工作的长期目标是在高磁场下实现低频EPR跃迁，这将使EPR成像的化学灵敏度与MRI相结合。双自旋系统的单重态到三重态跃迁由于其独特的场依赖性是实现这种EPR跃迁的一种很有希望的方法。然而，这种转变是被禁止的，因此是弱的，因此需要化学设计策略来覆盖EPR选择规则并增加信号强度。双核金属配合物具有过多的磁相互作用，可能潜在地违反EPR选择规则，但这些违反的有效性的实验测试尚未进行。这项工作将研究各种双核金属配合物中的单重态到三重态跃迁，以探索交换耦合、超精细耦合和相对自旋取向如何影响禁止共振的强度。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 & Mechanisms B Program of the Chemistry Division, Professor Joseph Zadrozny of the Department of Chemistry at Colorado State University is developing new classes of dinuclear transition metal complexes to probe forbidden electron paramagnetic resonance (EPR) spectroscopic transitions. The goal of this research is to exploit the characteristics of these dinuclear species to understand how molecular structure can assist in violating EPR selection rules to enable high intensity transitions. The specific transitions being explored may yield new capabilities for bioimaging techniques that use EPR transitions. The research project spans the interface of inorganic and physical chemistries with synthetic and spectroscopic analyses as a key part of the work. The broader outreach goals for the program will be to create an easy-to-access lesson for synthetic chemists to approach the selection rules of EPR. This plan will follow the pedagogical strategies commonly employed for more common techniques, e.g. UV-vis spectroscopy, and as such aims to be a cornerstone in bringing new chemists into the EPR arena.The longer-term goal for the work is to enable low-frequency EPR transitions at high magnetic field, which would permit the chemical sensitivity of EPR imaging to be integrated with MRI. The singlet-to-triplet transition of two-spin systems is a promising way to realize such an EPR transition, because of its unique field dependence. Yet, the transition is forbidden and therefore weak hence, chemical design strategies for molecules to override the EPR selection rule and increase signal intensity are needed. Dinuclear metal complexes have a plethora of magnetic interactions that could potentially violate the EPR selection rule, but experimental tests of the efficacy of these violations have yet to be performed. This work will study the singlet-to-triplet transition in a variety of dinuclear metal complexes to explore how exchange coupling, hyperfine coupling, and relative spin orientation all contribute to the intensity of the forbidden resonance.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.