聚合物机械化学†产生的多种可蜕变的二芳基乙腈自由基

Takumi Yamamoto, Daisuke Aoki, Koichiro Mikami and Hideyuki Otsuka
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引用次数: 0

摘要

荧光自由基作为发光材料备受关注,这主要是因为与闭壳分子相比,荧光自由基具有更高的发光效率。然而,在环境条件下分析荧光自由基仍然是一项具有挑战性的任务,因为自由基在空气中通常是不稳定的。此外,据我们所知,旨在通过改变取代基来控制荧光波长的研究尚未完成。在此,我们报告了通过聚合物机械化学反应生成的含有不同取代基的多种可蜕变二芳基乙腈(DAAN)自由基。通过球磨聚苯乙烯粉末和 DAAN 衍生物生成的 DAAN 自由基分散在聚苯乙烯基体中,它们在基体中保持自由基状态,从而可以测量固态荧光光谱。这些测量结果表明,只有通过改变这些 DAAN 自由基中芳香环上的取代基,才能实现从绿色到红色(λem,max = 517-635 nm)的宽范围荧光波长。这种现象在研究较多的三芳基甲基自由基中还没有观察到。这些 DAAN 自由基的荧光波长可通过与时间相关的密度-函数理论(TD-DFT)计算精确估算。我们结合 DFT 计算和实验结果讨论了球磨过程中产生的 DAAN 自由基的数量。我们的研究结果表明,与聚合物机械副产物的轨道相互作用、键解离焓以及自由基中心的立体保护对于 DAAN 自由基的生成至关重要。这项研究的结果有望为开发先进的荧光自由基提供有用的指导。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Diverse metastable diarylacetonitrile radicals generated by polymer mechanochemistry†

Diverse metastable diarylacetonitrile radicals generated by polymer mechanochemistry†

Fluorescent radicals have attracted great attention as luminescent materials, mostly on account of their potential to achieve higher luminescence efficiency than closed-shell molecules. However, analyzing fluorescent radicals at ambient conditions remains a challenging task, because radicals are usually unstable in air. In addition, to the best of our knowledge, research aimed at controlling fluorescence wavelengths through substituent changes has not yet been accomplished. Here, we report diverse metastable diarylacetonitrile (DAAN) radicals, which contain different substituents, generated by polymeric mechano-chemical reactions. The DAAN radicals, generated by ball-milling powdered polystyrene together with DAAN derivatives, were dispersed within the polystyrene matrix, where they retained their radical state, which allowed measuring solid-state fluorescence spectra. These measurements revealed that a wide range of fluorescence wavelengths from green to red (λem,max = 517–635 nm) can be achieved only by changing the substituents on the aromatic rings in these DAAN radicals. This phenomenon has not been observed for the well-studied triarylmethyl radicals. The fluorescence wavelength of these DAAN radicals can be precisely estimated by time-dependent density-functional theory (TD-DFT) calculations. The amount of DAAN radicals generated upon ball-milling is discussed in conjunction with DFT calculations and experimental results. Our results suggest that the orbital interactions with polymeric mechanoradicals, the bond-dissociation enthalpy, and the steric protection of the radical center are of paramount importance for the generation of DAAN radicals. The results of this study can be expected to provide useful guidelines for the development of advanced fluorescent radicals.

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