Ni Yong, Gordillo-Gámez Fernando, Peña Alvarez Miriam, Nan Zhihan, Li Zhengtao, Wu Shaofei, Han Yi, Casado Juan, Wu Jishan
Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 Singapore.
Department of Physical Chemistry, Faculty of Science, University of Málaga, CEI Andalucía Tech, Campus de Teatinos s/n, 29071 Málaga, Spain.
J Am Chem Soc. 2020 Jul 22;142(29):12730-12742. doi: 10.1021/jacs.0c04876. Epub 2020 Jul 10.
A three-dimensional π-conjugated polyradicaloid molecular cage , consisting of three Chichibabin's hydrocarbon motifs connected by two benzene-1,3,5-triyl bridgeheads, was synthesized. Compared with its linear model compound , the prism-like has a more rigid structure, which shows significant impact on the molecular dynamics, stability, and electronic properties. A higher rotation energy barrier for the quinoidal biphenyl units was determined in (15.64 kcal/mol) than that of (11.40 kcal/mol) according to variable-temperature NMR measurements, leading to improved stability, a smaller diradical character, and an increased singlet-triplet energy gap. The pressure-dependent Raman spectroscopic studies on the rigid cage revealed a quinoidal-to-aromatic transformation along the biphenyl bridges. In addition, the ellipsoidal cavity in the cage allowed selective encapsulation of fullerene C over C, with an associate constant of about 1.43 × 10 M. Moreover, and exhibited similar redox behavior and their cationic species ( and ) were obtained by chemical oxidation, and the structures were identified by X-ray crystallographic analysis. The biphenyl unit showed a twisted conformation in and remained coplanarity in . Notably, molecules of form a one-dimensional columnar structure via close π-π stacking between the bridgeheads.
合成了一种三维π共轭多自由基分子笼，它由三个通过两个苯-1,3,5-三基桥头连接的齐齐巴宾烃基序组成。与其线性模型化合物相比，棱柱状的该分子笼具有更刚性的结构，这对分子动力学、稳定性和电子性质有显著影响。根据变温核磁共振测量，该分子笼中醌型联苯单元的旋转能垒（15.64千卡/摩尔）高于其线性模型化合物（11.40千卡/摩尔），从而提高了稳定性，降低了双自由基特征，并增大了单重态-三重态能隙。对刚性分子笼进行的压力依赖拉曼光谱研究揭示了沿联苯桥的醌型到芳香型的转变。此外，分子笼中的椭球形空腔允许选择性地包封富勒烯C而不是C，缔合常数约为1.43×10 M。此外，该分子笼和另一种分子表现出相似的氧化还原行为，并且它们的阳离子物种（分别为和）通过化学氧化得到，其结构通过X射线晶体学分析确定。联苯单元在一种分子中呈扭曲构象，而在另一种分子中保持共平面。值得注意的是，一种分子的分子通过桥头之间紧密的π-π堆积形成一维柱状结构。
