Direct Observation of the Ultrafast Evolution of Open-Shell Biradical in Photochromic Radical Dimer
Direct Observation of the Ultrafast Evolution of Open-Shell Biradical in Photochromic Radical Dimer
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直接观察光致变色自由基二聚体中开壳双自由基的超快演化
DOI：
10.1021/jacs.7b01598
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发表时间：
2017
影响因子：
15
通讯作者：
and Jiro Abe
中科院分区：
文献类型：
--
作者：
Yoichi Kobayashi;Hajime Okajima;Hikaru Sotome;Takeshi Yanai;Katsuya Mutoh;Yusuke Yoneda;Yasuteru Shigeta;Akira Sakamoto;Hiroshi Miyasaka;and Jiro Abe
离域双自由基由于其对单重态双自由基的兴趣以及在双光子吸收材料等方面的潜在应用而得到了广泛的研究。然而，许多双自由基的研究只集中在刚性分子结构的静态性质。离域双自由基的双自由基性质对分子结构和局部环境的细微变化很敏感。因此，对该体系动力学性质的研究将有助于深入了解稳定自由基化学。在这项研究中，我们直接探测光致变色自由基二聚体，五芳基联咪唑（PABI）的离域双自由基的超快动力学，通过时间分辨的可见和红外光谱和量子化学计算与扩展的多态完全活性空间二级微扰理论（XMS-CASPT 2）。虽然光生瞬态物种被认为是一个单一的物种的双自由基，目前的超快光谱研究显示存在两个瞬态异构体不同的双自由基字符的贡献。这两种亚稳异构体的来源很可能是由于在咪唑环上取代的苯环之间的大量货车德瓦耳斯相互作用。揭示双自由基贡献的时间演化将激发探索新的离域双自由基和开发基于双自由基的光功能材料。
Delocalized biradicals have been extensively studied because of fundamental interests to singlet biradicals and several potential applications such as to two-photon absorption materials. However, many of the biradical studies only focus on the static properties of the rigid molecular structures. It is expected that the biradical properties of the delocalized biradicals are sensitive to the subtle changes of the molecular structures and their local environments. Therefore, the studies of the dynamic properties of the system will give further insight into stable radical chemistry. In this study, we directly probe the ultrafast dynamics of the delocalized biradical of a photochromic radical dimer, pentaarylbiimidazole (PABI), by time-resolved visible and infrared spectroscopies and quantum chemical calculations with the extended multistate complete active space second-order perturbation theory (XMS-CASPT2). While the photogenerated transient species was considered to be a single species of the biradical, the present ultrafast spectroscopic study revealed the existence of two transient isomers differing in the contributions of biradical character. The origin of the two metastable isomers is most probably due to the substantial van der Waals interaction between the phenyl rings substituted at the imidazole rings. Unraveling the temporal evolution of the biradical contribution will stimulate to explore novel delocalized biradicals and to develop biradical-based photofunctional materials utilizing the dynamic properties.