Xu Tingting, Han Yi, Ni Yong, Chi Chunyan
Department of Chemistry, National University of Singapore, 3 Science drive 3, 117543, Singapore, Singapore.
Angew Chem Int Ed Engl. 2025 Jan 10;64(2):e202414533. doi: 10.1002/anie.202414533. Epub 2024 Nov 2.
Organic radicals based dynamic covalent chemistry is promising in preparing stimuli-responsive chromic materials, due to their simplicity of dissociation/association, accompanied with distinct color changes during the process. However, suitable organic radicals for dynamic covalent chemistry have not been widely explored yet. Herein, a series of oxindolyl-based mono-radicals (OxRs) with different substituents were successfully synthesized and studied systematically as potential building blocks for stimuli-responsive chromic materials. These OxRs would dimerize spontaneously to form their corresponding dimers. The structures of dimers were unambiguously confirmed through low-temperature H NMR and single-crystal X-ray diffraction analyses. Dynamic interconversion between monomers and dimers was achieved by reversible cleavage and recovery of the σ-bond upon soft external stimuli (temperature, pressure, and solvent polarity), accompanied by significant color changes. It is interesting that the stability of the mono-radical could be tuned through changing different substituents, and consequently altering the bond dissociation energy of the dynamic covalent bond between monomers. These new OxRs characterized by appreciable properties are entitled to more opportunities in developing mechanochromic and thermochromic materials, where their responsiveness to stimuli can be readily controlled by the substituents adhered.
基于有机自由基的动态共价化学在制备刺激响应性变色材料方面具有广阔前景，这是因为其解离/缔合过程简单，且在此过程中伴有明显的颜色变化。然而，适用于动态共价化学的有机自由基尚未得到广泛探索。在此，一系列具有不同取代基的氧化吲哚基单自由基（OxRs）被成功合成，并作为刺激响应性变色材料的潜在构建单元进行了系统研究。这些OxRs会自发二聚形成其相应的二聚体。通过低温氢核磁共振（H NMR）和单晶X射线衍射分析明确证实了二聚体的结构。在温和的外部刺激（温度、压力和溶剂极性）下，通过σ键的可逆断裂和恢复实现了单体与二聚体之间的动态相互转化，同时伴有显著的颜色变化。有趣的是，单自由基的稳定性可以通过改变不同的取代基来调节，从而改变单体之间动态共价键的键解离能。这些具有显著特性的新型OxRs在开发机械变色和热致变色材料方面有更多机会，在这些材料中，它们对刺激的响应可以通过附着的取代基轻松控制。
