Kasemthaveechok Sitthichok, Abella Laura, Jean Marion, Cordier Marie, Roisnel Thierry, Vanthuyne Nicolas, Guizouarn Thierry, Cador Olivier, Autschbach Jochen, Crassous Jeanne, Favereau Ludovic
Université Rennes, CNRS, ISCR-UMR 6226, Rennes F-35000, France.
Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260, United States.
J Am Chem Soc. 2020 Nov 17. doi: 10.1021/jacs.0c08948.
We report persistent chiral organic mono- and diradical cations based on bicarbazole molecular design with an unprecedented stability dependence on the type of chirality, namely, axial versus helical. An unusual chemical stability was observed for sterically unprotected axial bicarbazole radical in comparison with monocarbazole and helical bicarbazole ones. Such results were experimentally and theoretically investigated, revealing an inversion in energy of the singly occupied molecular orbital (SOMO) and the highest (doubly) occupied molecular orbital (HOMO) in both axial and helical bicarbazole monoradicals along with a subtle difference of electronic coupling between the two carbazole units, which is modulated by their relative dihedral angle and related to the type of chirality. Such findings allowed us to explore in depth the SOMO-HOMO inversion (SHI) in chiral radical molecular systems and provide new insights regarding its impact on the stability of organic radicals. Finally, these specific electronic properties allowed us to prepare a persistent, intrinsically chiral, diradical which notably displayed near-infrared electronic circular dichroism responses up to 1100 nm and almost degenerate singlet-triplet ground states with weak antiferromagnetic interactions evaluated by magnetometry experiments.
我们报道了基于双咔唑分子设计的持久性手性有机单自由基和双自由基阳离子，其稳定性对手性类型（即轴向与螺旋）具有前所未有的依赖性。与单咔唑和螺旋双咔唑相比，空间位阻未受保护的轴向双咔唑自由基表现出不同寻常的化学稳定性。我们通过实验和理论研究了这些结果，揭示了轴向和螺旋双咔唑单自由基中单占据分子轨道（SOMO）和最高（双）占据分子轨道（HOMO）的能量反转，以及两个咔唑单元之间电子耦合的细微差异，这种差异由它们的相对二面角调节，并与手性类型相关。这些发现使我们能够深入探索手性自由基分子系统中的SOMO-HOMO反转（SHI），并为其对有机自由基稳定性的影响提供新的见解。最后，这些特定的电子性质使我们能够制备一种持久性的、内在手性的双自由基，其在高达1100 nm处显著显示近红外电子圆二色性响应，并且通过磁力测量实验评估，其单重态-三重态基态几乎简并，具有弱反铁磁相互作用。
