在超分子有機框架中設計非本源性孔隙性：利用巨型四面體分子進行結構調控

Abstract

在超分子有機框架（supramolecular organic frameworks, SOFs）中構築具熱穩定性且結構明確的孔洞，仍是一項根本性的挑戰，特別是在使用巨型四面體構建單元時。儘管這類具剛性與高對稱性的分子在拓樸上具有構築三維多孔結構的潛力，但在自組裝過程中往往因幾何互鎖（geometry interlocking）的傾向，而導致形成緊密堆疊的柱狀結構，進而排除了孔洞的生成。在本研究中，我們提出一種基於給體幾何設計的共組裝策略，透過巨型四面體受體分子TetraNDI與一系列多Py臂 pyrene衍生物（Pyx, x = 2–4）之間的電荷轉移（charge-transfer, CT）作用，以調控自組裝行為並突破孔洞形成的限制。 研究結果顯示，Py4與Py3可與TetraNDI組裝形成電荷轉移錯合物，進而產生具高熱穩定性的一維超分子柱狀結構；而僅具兩個Py臂的Py2，則傾向形成兩親性棒狀單元，再進一步堆疊為二維層狀結構。光譜分析與臨場廣角X光散射（in-situ WAXS）實驗證實這些錯合體具有明確的CT驅動自組裝結構。值得注意的是，僅有TetraNDI:Py3系統能夠形成具明確定義之非本源性孔洞，且可穩定嵌入一當量pyrene分子而不破壞骨架結構。這類孔隙源自於Py3分子先天缺少一個Py臂所產生的幾何空缺，進而提供客體分子可進入的位點。 相對而言，完全交錯嵌合的TetraNDI:Py4柱狀結構與緊密堆積的 TetraNDI:Py2層狀結構皆缺乏可進入的孔洞，且在引入pyrene客體後出現結構無序化現象。這些發現揭示，給體分子幾何的微小變化可明確調控巨型四面體分子於SOF系統中的互鎖行為與孔洞生成，提供一項可應用於CT錯合體設計的原則，得以繞過巨型正四面體單元的緊密堆積限制，實現具熱穩定性的非共價多孔結構。此策略為構築具孔洞環境可調性之超分子材料開啟新途，並具潛力應用於氣體儲存與分子分離等領域。

Constructing thermally stable and structurally well-defined porosity within supramolecular organic frameworks (SOFs) remains a fundamental challenge, particularly when employing large tetrahedral building blocks. Although such rigid, high-symmetry molecules offer topological potential for three-dimensional porous architectures, their tendency to engage in geometry interlocking during self-assembly often leads to close-packed columnar structures that preclude pore formation. Herein, we demonstrate a donor-geometry-directed co-assembly strategy that circumvents this limitation by leveraging charge-transfer (CT) interactions between a giant tetrahedral acceptor (TetraNDI) and a series of multi-armed pyrene-based donors (Pyx, x = 2–4). Our results show that Py4 and Py3 promote interlocking CT complexes with TetraNDI to form thermally robust one-dimensional (1D) supramolecular columns, while Py2, bearing only two arms, yields amphiphilic supramolecular rods that pack into two-dimensional (2D) lamellar phases. Spectroscopic and in-situ wide-angle X-ray scattering (in-situ WAXS) measurements confirm the formation of distinct CT architectures. Notably, only the TetraNDI:Py3 system enables the formation of well-defined extrinsic micropores capable of accommodating one equivalent of pyrene without disrupting the supramolecular scaffold. This porosity arises from a geometric vacancy inherent to Py3—one fewer Py arm than Py4—which creates a guest-accessible cavity. In contrast, the fully interdigitated TetraNDI:Py4 columns and the densely packed lamellar TetraNDI:Py2 structures lack such accessible voids and exhibit guest-induced disorder upon pyrene loading. These findings reveal that subtle variations in donor geometry can deterministically modulate interlocking behavior and porosity in CT-driven SOFs, offering a design principle for bypassing the packing constraints of tetrahedral units and realizing stable noncovalent porous frameworks. This approach opens a path toward supramolecular materials with tailored pore environments and potential applications in molecular separations and gas storage.