Organic radicals are open-shell species and have been extensively applied to functional materials due to their unique physicochemical properties with unpaired electrons; however, most of them are highly reactive and short-lived. Herein, a series of stable radicals were readily accessed in two steps from a bis(imino)acenaphthene-supported N-heterocyclic carbene (IPr(BIAN)) through enhancing the delocalization of spin density. The IPr(BIAN)-based radicals 3a–c, obtained by reduction of the corresponding iminium salts 2a–c with KC₈, have been spectroscopically and crystallographically (3a,c) characterized. DFT calculations indicate that increasing the electron-withdrawing properties of the para substituent on the carbene carbon atom results in the spin density evolving from the acenaphthene ring to the phenyl ring. The IPr(BIAN)-based radicals 3a–c show excellent stability: they have half-lives of 1 week in well-aerated solutions and feature a high thermal decomposition temperature up to 200 °C.

中文翻译：

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源自退火的 N-杂环卡宾的空气/热稳定结晶碳中心自由基

有机自由基是开壳物质，由于其独特的物理化学性质和不成对电子而被广泛应用于功能材料；然而，它们中的大多数是高度反应性和短暂的。在本文中，通过增强自旋密度的离域化，可以很容易地从双（亚氨基）苊负载的 N-杂环卡宾（IPr（BIAN））分两步获得一系列稳定的自由基。通过用 KC ₈还原相应的亚胺盐2a – c获得的基于 IPr(BIAN) 的自由基3a – c已经在光谱和晶体学上进行了光谱分析 ( 3a , c) 表征。DFT 计算表明，增加卡宾碳原子上对位取代基的吸电子特性会导致自旋密度从苊环演变为苯环。基于 IPr(BIAN) 的自由基3a – c显示出优异的稳定性：它们在通风良好的溶液中的半衰期为 1 周，并且具有高达 200 °C 的高热分解温度。