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教授正在开发新的双核过渡金属络合物，以探测被禁电子顺磁共振(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有助于违反EPR选择规则来实现高强度跃迁。正在探索的特定转变可能会为使用EPR转变的生物成像技术带来新的能力。该研究项目跨越了无机化学和物理化学的界面，将合成和光谱分析作为工作的关键部分。该计划的更广泛的推广目标将是为合成化学家创造一个易于获取的课程，以接近EPR的选择规则。这项计划将遵循更常见技术常用的教学策略，例如UV-Vis光谱学，并因此旨在成为将新的化学家引入EPR领域的基石。这项工作的长期目标是实现高磁场下的低频EPR跃迁，这将使EPR成像的化学敏感性与MRI相结合。双自旋系统的单重态到三重态的跃迁是实现这种EPR跃迁的一种很有前途的方法，因为它具有独特的场依赖性。然而，这种转变是被禁止的，因此很弱，因此需要分子的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，可能会违反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络合物中的单重态到三重态的转变，以探索交换耦合、超精细耦合和相对自旋取向如何都有助于禁止共振的强度。这一奖项反映了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。

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.