Fig. 2: Physical characterisation of multivariate COFs.

a, b Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC HAADF STEM) images and (c) corresponding elemental mappings of the synthesised BECOF. Scale bars, a 5 nm; b 1 nm; c 50 nm. d X-ray diffraction (XRD) patterns, e Fourier transform infrared (FTIR) spectra, f 13C solid-state nuclear magnetic resonance (SSNMR) spectra, g X-ray photoelectron spectroscopy (XPS) survey spectra, and (h) high-resolution N 1s XPS spectra of BCOF, BECOF, and ECOF.