Pagoda[4]arene and <i>i</i>‑Pagoda[4]arene

A new type of macrocyclic arenes, named pagoda[4]­arene (P4) and i-pagoda­[4]­arene (i-P4), were conveniently synthesized by the TFA-catalyzed one-pot condensation of 2,6-di­meth­oxy­lanthra­cene and para­form­aldehyde in dichloromethane at room temperature. P4 and i-P4 showed unique square pagoda structures and fixed conformations in solution and also exhibited strong blue fluorescence. Moreover, P4 and i-P4 with deep and rich-electron cavities could not only encapsulate n-hexane and one or two dichloromethane molecules in the solid state but also showed strong binding abilities toward neutral dinitriles with different chain lengths and various nitrogen-containing heterocyclic salts to form 1:1 stable host–guest complexes in both solution and the solid state. In particular, it was also found that with the increase in the alkyl chain length of the dinitriles, the association constants for their complexes with both P4 and i-P4 were markedly increased from glutaronitrile to octanedinitrile as a result of the deep cavities of the macrocycles and multiple intermolecular interactions. Since P4 and i-P4 had stable planar chirality, their efficient resolutions were further achieved by HPLC with a chiral column. Interestingly, the two enantiomers showed mirror-imaged CD signals and excellent CPL properties, which could allow them to have potential applications in chiral luminescent materials.一类新型大环芳烃（macrocyclic arene），分别命名为宝塔[4]芳烃（pagoda[4]arene，P4）与异宝塔[4]芳烃（i-pagoda[4]arene，i-P4），可通过三氟乙酸（trifluoroacetic acid，TFA）催化的一锅法缩合反应便捷合成：以2,6-二甲氧基蒽（2,6-dimethoxyanthracene）与多聚甲醛（paraformaldehyde）为原料，在二氯甲烷（dichloromethane）中室温下反应即可得到目标产物。P4与i-P4均展现出独特的方形塔状结构，在溶液中呈现固定构象，同时具备较强的蓝色荧光发射性能。此外，P4与i-P4拥有深邃且富电子的空腔，不仅可在固态下包合正己烷（n-hexane）以及1个或2个二氯甲烷分子，还对不同链长的中性二腈类化合物以及各类含氮杂环盐展现出优异的结合能力，可在溶液与固态体系中均形成1:1的稳定主客体复合物（host-guest complex）。尤为值得关注的是，研究发现随着二腈类化合物烷基链长度的增加，其与P4、i-P4形成的复合物的结合常数（association constant）从戊二腈（glutaronitrile）到辛二腈（octanedinitrile）显著升高，这归因于大环芳烃的深邃空腔与多重分子间相互作用。鉴于P4与i-P4具有稳定的平面手性（planar chirality），本研究进一步通过手性高效液相色谱（High Performance Liquid Chromatography，HPLC）柱实现了其高效拆分。有趣的是，该类对映异构体展现出镜像对称的圆二色（Circular Dichroism，CD）信号与优异的圆偏振发光（Circularly Polarized Luminescence，CPL）性能，使其在手性发光材料领域具备潜在应用价值。