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 arenes）被成功合成，其被命名为塔状[4]芳烃（pagoda[4]arene, P4）与异塔状[4]芳烃（i-pagoda[4]arene, i-P4）。二者可通过三氟乙酸（TFA）催化的一锅法缩合，以2,6-二甲氧基蒽（2,6-dimethoxyanthracene）与多聚甲醛为原料，在二氯甲烷（dichloromethane）中于室温下便捷合成。P4与i-P4均展现出独特的方形塔状结构，在溶液中拥有固定构象，同时表现出强烈的蓝色荧光。此外，具备深邃富电子空腔的P4与i-P4，不仅可在固态下包合正己烷（n-hexane）以及1~2个二氯甲烷分子，还对不同链长的中性二腈类化合物（dinitriles）与各类含氮杂环盐展现出优异的结合能力，可在溶液与固态中均形成1:1化学计量比的稳定主客体复合物（host-guest complexes）。尤为值得注意的是，研究发现随着二腈类化合物烷基链长度的增加，P4与i-P4与之形成的复合物的结合常数（association constants）从戊二腈（glutaronitrile）到辛二腈（octanedinitrile）显著提升，这归因于大环芳烃的深邃空腔与多重分子间相互作用（intermolecular interactions）。由于P4与i-P4具有稳定的平面手性（planar chirality），后续通过手性柱高效液相色谱（HPLC）实现了二者的高效拆分。有趣的是，这两种对映异构体（enantiomers）展现出镜像对称的圆二色（CD, Circular Dichroism）信号与优异的圆偏振发光（CPL, Circular Polarized Luminescence）性能，使其在手性发光材料领域具备潜在应用价值。