Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526, Japan.
Hiroshima University Research Center for, Photo-Drug-Delivery Systems (HiU-P-DDS), 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526, Japan.
Chemistry. 2018 Oct 1;24(55):14808-14815. doi: 10.1002/chem.201803076. Epub 2018 Sep 6.
Localized singlet diradicals have attracted much attention, not only in the field of bond-homolysis chemistry, but also in nonlinear optical materials. In this study, an extremely long lived localized singlet diradical was obtained by using a new molecular design strategy in which it is kinetically stabilized by means of a macrocycle that increases the molecular strain of the corresponding σ-bonded compound. Notably, the lifetime of this diradical (14 μs) is two orders of magnitude longer than that of a standard singlet diradical without a macrocyclic structure (≈0.2 μs) at 293 K. The species is persistent below a temperature of 100 K. In addition to the kinetic stabilization of the singlet diradical, the spontaneous oxidation of its corresponding ring-closed compound at 298 K produced oxygenated products under atmospheric conditions. Apparently, the "stretch effect" induced by the macrocyclic structure plays a crucial role in extending the lifetime of localized singlet diradicals and increasing the reactivity of their corresponding σ-bonded compounds.
局域单重态自由基引起了广泛关注，不仅在键均裂化学领域，而且在非线性光学材料领域也是如此。在这项研究中，通过使用新的分子设计策略获得了一个极其稳定的局域单重态自由基，该策略通过增加相应σ键合化合物的分子应变来实现动力学稳定。值得注意的是，与没有大环结构的标准单重态自由基（≈0.2 μs）相比，该自由基（14 μs）在 293 K 下的寿命长两个数量级。该自由基在低于 100 K 的温度下仍然稳定存在。除了单重态自由基的动力学稳定之外，其相应的闭环化合物在 298 K 下的自发氧化在大气条件下产生了含氧产物。显然，大环结构引起的“拉伸效应”在延长局域单重态自由基的寿命和增加其相应σ键合化合物的反应性方面起着关键作用。
