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

新型稳定有机中性自由基的合成和对具有高度离域不成对电子的π-电子系统的理解，对新型有机分子基磁性材料的分子设计具有重要意义。6-氧苯烯氧基衍生物最初是在苯烯基体系的基础上设计的，具有很高的持久性，足以在空气中处理。有趣的是，该中性π-自由基体系具有与母体苯烯基体系相似的“极度自旋离域和高度自旋极化性质”，而自旋密度分布的拓扑结构与苯烯基体系形成鲜明对比。6-氧苯烯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由苯烯基骨架上两个氧原子的连性引起的π共轭单基体系自旋密度分布的拓扑对称性控制。在制备6-氧苯烯氧基体系拓扑异构体、3-氧苯烯氧基和4-氧苯氧基的基础上，对这一新概念进行了阐述和实验验证。此外，我们已经成功地测定了这些氧苯氧基衍生物的x射线晶体结构，并证明了基于苯基中性π自由基的大分子间磁交换相互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.