Exploration of Neutral Radical Systems Based on Oxophenalenoxyl as New Spin Source

新型稳定的有机中性自由基的合成和对具有高度离域未成对电子的π电子系统固有的理解在新型有机分子基磁性材料的分子设计中起着至关重要的作用。6-氧苯氧基衍生物最初是在苯基体系的基础上设计的，表现出足够高的持久性，足以在空气中操作。有趣的是，这种中性的π-自由基体系的独特之处在于表现出类似于母体苯基体系的“极端自旋离域和高度自旋极化的性质”，而自旋密度分布的拓扑结构与苯基体系的自旋密度分布拓扑结构形成鲜明对比。6-氧基苯氧基衍生物电子自旋结构的这些显著特征使我们能够讨论π共轭单轨体系中自旋密度分布的拓扑对称性控制，这些自旋密度分布源于苯环骨架上两个氧原子的连接性。这一新概念是在制备6-氧基苯氧基、3-和4-氧苯基苯氧基的拓扑异构体的基础上进行的。此外，我们还成功地测定了这些氧-苯基苯氧基衍生物的X-射线晶体结构，并证明了对苯基中性π-自由基大分子间磁交换作用的晶体工程是可行的。

Syntheses of novel stable organic neutral radicals and understanding inherent in π-electronic systems with highly delocalized unpaired electrons play a crucial role in the molecular designs for novel intriguing organic molecule-based magnetic materials. 6-Oxophenalenoxyl derivatives were originally designed on the basis of the phenalenyl system, and showed high persistency enough to handle in air. Interestingly, this neutral π-radical system found to be unique in exhibiting both an "extremely spin-delocalized and highly spin-polarized nature" similar to that of the parent phenalenyl system, while the topology of the spin density distribution sharply contrasted with that of the phenalenyl system. These salient features in the electronic spin structures of 6-oxophenalenoxyl derivative enable us to discuss topological-symmetry control in spin density distribution in π-conjugated monoradical systems originating from the connectivities of the two oxygen atoms on the phenalenyl skeleton. This new concept was elucidated and exemplified experimentally on the basis of the preparation of topological isomers of 6-oxophenalenoxyl system, 3-and 4-oxophenalenoxyls. Furthermore, we have succeeded in the determinations of X-ray crystal structures of these oxophenalenoxyl derivatives, and demonstrated feasible crystal engineering for large intermolecular magnetic exchange interactions of phenalenyl-based neutral π-radicals.