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

Lu Liu,Yinghua Jin,Weitao Gong,Jingnan Cui,Wei Zhang,Shaofeng Huang,Yiming Hu

doi:10.1039/d1sc03680g

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.

Highlights

Covalent organic frameworks (COFs) represent a class of crystalline porous materials constructed with diverse organic building blocks via covalent bonds.1–5 Featuring high surface area, large pore volume, high chemical/thermal stability, and tunable pore topologies, COFs have become a promising platform for gas adsorption and separation,6–10 comparable to conventional porous materials, such as zeolites and metal– organic frameworks (MOFs).11–13 speci c supramolecular host–guest interactions, which have been commonly employed in the solution phase to realize selective molecular binding, have rarely been explored in the COF system.14,15 One possible way to address this issue is to incorporate macrocyclic cavitands into COFs
Integration of well-defined discrete macrocyclic hosts into ordered porous polymeric frameworks 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
pillar[5] arene-based COF (P5-COF) and Model-COF were characterized by FT-IR spectroscopy, 13C cross-polarization magic-angle spinning (CP-MAS) NMR spectroscopy, thermogravimetric analysis (TGA), SEM and powder X-ray diffraction (PXRD) analysis

Summary

Introduction

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. Pillar[n]arenes,21–23 a class of macrocyclic cavitands with intrinsic con ned pores and selective guest binding capability, are attractive candidates for integration into COFs as host molecules.24–26 interesting molecular recognition properties of pillar[n]arenes in the solution phase have been demonstrated, they generally exhibit poor guest binding capability in the solid state due to their random packing.27–32 The opening channels are largely blocked, and the intrinsic cavities are buried inside the solid matrix and not accessible to the guest species.33,34 the supramolecular structures assembled via noncovalent interactions are vulnerable and tend to collapse upon guest removal.35,36 it is challenging to maintain the permanent porosity and selective guest binding properties of pillar[n]arenes in the solid state.

Results

Conclusion