Facile transformation of imine covalent organic frameworks into ultrastable crystalline porous aromatic frameworks

Xinle Li,Xiaohe Lei,Songliang Cai,Yi Liu,Jim Ciston,Emory M Chan,Changlin Zhang,Fang Hong,Jeffrey J Urban,Virginia Altoe

doi:10.1038/s41467-018-05462-4

Abstract

The growing interest in two-dimensional imine-based covalent organic frameworks (COFs) is inspired by their crystalline porous structures and the potential for extensive π-electron delocalization. The intrinsic reversibility and strong polarization of imine linkages, however, leads to insufficient chemical stability and optoelectronic properties. Developing COFs with improved robustness and π-delocalization is highly desirable but remains an unsettled challenge. Here we report a facile strategy that transforms imine-linked COFs into ultrastable porous aromatic frameworks by kinetically fixing the reversible imine linkage via an aza-Diels-Alder cycloaddition reaction. The as-formed, quinoline-linked COFs not only retain crystallinity and porosity, but also display dramatically enhanced chemical stability over their imine-based COF precursors, rendering them among the most robust COFs up-to-date that can withstand strong acidic, basic and redox environment. Owing to the chemical diversity of the cycloaddition reaction and structural tunability of COFs, the pores of COFs can be readily engineered to realize pre-designed surface functionality.

Highlights

The growing interest in two-dimensional imine-based covalent organic frameworks (COFs) is inspired by their crystalline porous structures and the potential for extensive π-electron delocalization
The viability of the Povarov reaction was first demonstrated on a prototype iminelinked COF, a highly crystalline and porous COF denoted as COF-131
Comparison of the Fourier-transform infrared (FT-IR) spectra of MF-1a and COF-1 (Fig. 2a) revealed a new cluster of peaks at ~1600 cm−1 that correspond to the stretch of aromatic quinoline core[30] and blue shift of the C–C=N-C stretch after the reaction

Summary

Introduction

The growing interest in two-dimensional imine-based covalent organic frameworks (COFs) is inspired by their crystalline porous structures and the potential for extensive π-electron delocalization. We report a more versatile approach to kinetically fix the reversible linkage in imine COFs to afford crystalline and chemically robust porous 2D aromatic framework with extended π-electron delocalization (Fig. 1a).

Results

Conclusion