School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, People's Republic of China.
Phys Chem Chem Phys. 2023 Jun 28;25(25):16991-17000. doi: 10.1039/d3cp01611k.
Magnetic conversion can be accomplished in a variety of ways, as organic molecules with switchable magnetic characteristics offer numerous technological applications. It is crucial to find magnetism-switchable systems because, in the field of organic magnetic materials, the redox-induced magnetic reversal is very simple to achieve and shows significant applications. Herein, we computationally design isoalloxazine-based diradicals through oxidizing N10 and adding a nitroxide to C8 as the spin source ( 8-nitroxide-isoalloxazine 10-oxide, an -phenylene-like nitroxide diradical expanded with a redox unit as a side-modulator) and its N1/N5-hydrogenated/protonated diradical derivatives and introducing substituents (-OH, -NH, and -NO) to C6. We demonstrate that the basically modified structure exhibits ferromagnetic (FM) characteristics with a magnetic coupling constant () of 561.3 cm calculated at the B3LYP/6-311+G(d,p) level, obeying the -phenylene-mediated diradical character, and dihydrogenation can lead to an AFM diradical with considerably large (-976.1 cm). Surprisingly, protonation at N1 or N5 can lead to distinctly different magnetic variations (561.3 → -1602.9 cm at N1 561.3 → 379.1 cm at N5). Analyses indicate that small singlet-triplet energy gaps and small energy gaps between the highest occupied and lowest unoccupied molecular orbitals (HOMO, LUMO) of the closed shell singlet state are the key features of these isoalloxazine diradicals, and aromaticity variations, significant spin delocalization from the π-conjugated structure and spin polarization from the non-Kekule structure induced by modification are responsible for the magnetic conversion. Furthermore, the spin alternation rule, the singly occupied molecular orbital (SOMO) effect, and the SOMO-SOMO energy splitting of the triplet state are used to analyze these distinct variations. This work provides a novel understanding of the structures and characteristics of modified isoalloxazine diradicals, as well as essential details for the intricate design and characterization of new isoalloxazine-based potential organic magnetic switches.
磁性转换可以通过多种方式实现，因为具有可切换磁性特性的有机分子提供了许多技术应用。找到磁开关系统至关重要，因为在有机磁性材料领域，氧化还原诱导的磁反转非常简单，并且具有重要的应用。在此，我们通过氧化 N10 并在 C8 上添加一个氮氧自由基作为自旋源（8-氮氧自由基-异咯嗪 10-氧化物，一个带有氧化还原单元作为侧调节剂的 - 苯并类似氮氧自由基二自由基）及其 N1/N5-氢化/质子化二自由基衍生物，并在 C6 上引入取代基（-OH、-NH 和-NO），计算设计了基于异咯嗪的二自由基。我们证明，在 B3LYP/6-311+G(d,p)水平下计算得到的基本修饰结构具有铁磁（FM）特性，磁耦合常数 () 为 561.3 cm，符合 - 苯并类似氮氧自由基二自由基的特征，并且氢化可以导致具有相当大的大 () 的反铁磁二自由基（-976.1 cm）。令人惊讶的是，在 N1 或 N5 上质子化可以导致明显不同的磁变化（在 N1 时为 561.3→-1602.9 cm，在 N5 时为 561.3→379.1 cm）。分析表明，小的单重态-三重态能隙和闭壳单重态最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）之间的小能隙是这些异咯嗪二自由基的关键特征，芳香性变化、从π共轭结构的显著自旋离域和由修饰引起的非 Kekule 结构的自旋极化导致了磁性转换。此外，自旋交替规则、三重态的单占据分子轨道（SOMO）效应和三重态的 SOMO-SOMO 能分裂用于分析这些明显的变化。这项工作提供了对修饰异咯嗪二自由基的结构和特性的新认识，以及对新异咯嗪基潜在有机磁开关的复杂设计和表征的重要细节。
