Topology, Distance, and Orbital Symmetry Effects on Electronic Spin–Spin Couplings in Rigid Molecular Systems: Implications for Long-Distance Spin–Spin Interactions
Topology, Distance, and Orbital Symmetry Effects on Electronic Spin–Spin Couplings in Rigid Molecular Systems: Implications for Long-Distance Spin–Spin Interactions
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刚性分子系统中电子自旋-自旋耦合的拓扑、距离和轨道对称性效应：对长距离自旋-自旋相互作用的影响
DOI：
10.1021/acs.jpca.0c06112
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Therien, Michael J.
中科院分区：
文献类型：
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作者：
Wang, Ruobing;Ko, Chih-Hung;Brugh, Alexander M.;Bai, Yusong;Forbes, Malcolm D.;Therien, Michael J.
了解biradecaloid中电子自旋-自旋耦合的符号和大小的基础因素，特别是那些集成到高度离域电子结构中的因素，有望为分子自旋电子系统的设计提供信息。使用稳态和变温电子顺磁共振（EPR）光谱，我们研究了对称的，强π共轭双[（卟啉）铜]（双[PCu]）系统的自旋动力学和探测原子特定的大环自旋密度，卟啉到卟啉连接拓扑结构，和轨道对称性的电子自旋-自旋耦合的幅度超过大量的Cu-Cu距离所发挥的作用。这些研究检查了以下：（i）具有低聚炔间隔基的内消旋-内消旋-连接的双[PCu]系统，（ii）内消旋-内消旋-桥接的双[PCu]阵列，其中PCu中心被单个乙炔基单元或多个5，15-二乙炔基（卟啉合）锌（II）单元分开，以及（iii）相应的β-至-β-桥接的双[PCu]结构。EPR数据表明，对于β-to-β-bridged体系和meso-to-meso-linked bis[PCu]结构，通过σ-键偶联机制控制平均交换作用（Javg）.相比之下，由单个乙炔基或多个5，15-二乙炔基（卟啉合）锌（II）单元分隔的PCu中心显示ln[Javg]相对于Cu-Cu σ-键分离数的现象学衰减，每个键为1.000.115，是这些其他组合物的一半，与π介导的自旋-自旋耦合的重要性一致。这些差异来自追溯其起源的大环-大环连接拓扑结构的性质和这些电子离域结构的前沿轨道流形内的Cu dx 2-y2单占据分子轨道的相对能量的影响。这项工作提供了深入了解的方法来调整的自旋交换相互作用和距离依赖的电子自旋-自旋耦合幅度在刚性，高度共轭biradecaloid的程度。
Understanding factors that underpin the signs and magnitudes of electron spin–spin couplings in biradicaloids, especially those that are integrated into highly delocalized electronic structures, promises to inform the design of molecular spintronic systems. Using steady-state and variable temperature electron paramagnetic resonance (EPR) spectroscopy, we examine spin dynamics in symmetric, strongly π-conjugated bis[(porphinato)copper] (bis[PCu]) systems and probe the roles played by atom-specific macrocycle spin density, porphyrin-to-porphyrin linkage topology, and orbital symmetry on the magnitudes of electronic spin–spin couplings over substantial Cu–Cu distances. These studies examine the following: (i)meso-to-meso-linked bis[PCu] systems having oligoyne spacers, (ii)meso-to-meso-bridged bis[PCu] arrays in which the PCu centers are separated by a single ethynyl unit or multiple 5,15-diethynyl(porphinato)zinc(II) units, and (iii) the corresponding β-to-β-bridged bis[PCu] structures. EPR data show that, for β-to-β-bridged systems andmeso-to-meso-linked bis[PCu] structures having oligoyne spacers, a through σ-bond coupling mechanism controls the average exchange interaction (Javg). In contrast, PCu centers separated by a single ethynyl or multiple 5,15-diethynyl(porphinato)zinc(II) units display a phenomenological decay of ln[Javg] versus Cu–Cu σ-bond separation number of ∼0.115 per bond, half as large as for these other compositions, congruent with the importance of π-mediated spin–spin coupling. These disparities derive from effects that trace their origin to the nature of the macrocycle–macrocycle linkage topology and the relative energy of the Cu dx2–y2singly occupied molecular orbital within the frontier orbital manifold of these electronically delocalized structures. This work provides insight into approaches to tune the extent of spin exchange interactions and distance-dependent electronic spin–spin coupling magnitudes in rigid, highly conjugated biradicaloids.