A pillar[5]arene-based covalent organic framework with pre-encoded selective host-guest recognition

Abstract

It is highly desirable to maintain both permanent accessible pores and selective molecular recognition capability of macrocyclic cavitands in the solid state. Integration of well-defined discrete macrocyclic hosts into ordered porous polymeric frameworks (e.g., covalent organic frameworks, COFs) represents a promising strategy to transform many supramolecular chemistry concepts and principles well established in the solution phase into the solid state, which can enable a broad range of practical applications, such as high-efficiency molecular separation, heterogeneous catalysis, and pollution remediation. However, it is still a challenging task to construct macrocycle-embedded COFs. In this work, a novel pillar[5]arene-derived (P5) hetero-porous COF, denoted as P5-COF, was rationally designed and synthesized. Featuring the unique backbone structure, P5-COF exhibited selective adsorption of C₂H₂ over C₂H₄ and C₂H₆, as well as significantly enhanced host-guest binding interaction with paraquat, in comparison with the pillar[5]arene-free COF analog, Model-COF. The present work established a new strategy for developing COFs with customizable molecular recognition/separation properties through the bottom-up "pre-porous macrocycle to porous framework" design.

Scheme 1. Synthetic routes to P5-COF and Model-COF.

Fig. 1. (a) Experimental and simulated PXRD patterns of P5-COF; (b) N₂ adsorption isotherms of P5-COF at 77 K; (c and d) top view (c) and side view (d) of P5-COF in the AA stacking model. The green dash indicates the CH–π stabilizing interactions.

Fig. 2. (a) Langmuir adsorption isotherms of paraquat by P5-COF and Model-COF. Inset: the comparison of the paraquat adsorption capacity of P5-COF and Model-COF; (b) gas adsorption isotherms of P5-COF (red) and Model-COF (blue) at 273 K; (c) comparison of gas adsorption uptakes of P5-COF and Model-COF at 273 K.