Fig. 2 | Nature Communications

Fig. 2

From: Solvatochromic covalent organic frameworks

Fig. 2

Structure analysis and solvatochromism of the Py–TT COF bulk powder. a Experimental PXRD pattern (black dots) of the Py–TT COF powder. Rietveld refinement (red line) using the structure model displayed in b provides a very good fit to the experimental data with only minimal differences between the experimental and the refined patterns (green line). Rwp = 4.9%, Rp = 10.5%. Bragg positions are indicated by blue ticks. Inset, magnified view of the 2θ > 9° region. b Top view (left) and side view (right) of the corresponding unit cell reveal the pseudo-quadratic, offset-stacked structure that is typical for pyrene-based COFs. Crystallographic data are available as Supplementary Data 1. The structure has a Connolly surface of 2139 m2 g−1, an accessible surface area of 1808 m2 g−1 and a pore volume of 1.01 cm3 g−1. c Nitrogen sorption isotherm of the Py–TT COF recorded at 77 K. Inset, QSDFT calculation using an equilibrium model yields a very narrow pore size distribution with a maximum at 2.1 nm. d High-resolution TEM image showing the large crystal domains of the Py–TT COF. Scale bar: 40 nm. Inset, magnified view onto a COF crystallite visualizing the pseudo-quadratic arrangement of the COF pores with a periodicity of 2.6 ± 0.1 nm. Scale bar: 20 nm. e Diffuse reflectance spectra of the dry (orange) and water vapour-saturated (brown) Py–TT COF powder showing a strong solvatochromic red-shift

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