Extended Data Fig. 4: Structure analysis and solvent-induced phase transformations of the hexPDI-1P COF.
(a) PXRD analysis of the dry hexPDI-1P COF. Rietveld refinement (red line) using the structure model shown in the inset provides a very good fit to the PXRD data (black dots) with only small differences between experimental and the refined patterns. Rwp = 9.1% (w/o background), Rp = 10.7%. Inset: The COF is strongly contracted along the a axis. Its porosity is very limited and not accessible to N2 or larger molecules (Connolly surface shown in light blue). The dry hexPDI-1P COF closely resembles the buPDI-1P COF cp phase where the alkyl chains are bent sidewards to allow for a closer packing of the PDI columns. (b) PXRD analysis of the toluene-loaded hexPDI-1P COF. Pawley refinement (red line) provides a good fit to the PXRD data (black dots). Rwp = 14% (w/o background), Rp = 3.2%. Inset: Force-field optimised structure model of the COF. In this phase, the COF has an open-pore configuration (Connolly surface shown in light blue). The hexyl chains are straight and adopt a side-by side configuration that closely resembles the buPDI-1P COF ip phase. Note: An op phase where the alkyl chains adopt a head-to-head configuration is not observed for this COF, even at high toluene loading. This is most likely due to steric reasons (the hexyl chains are too long). (c,d) Solvent-induced structural transformations monitored by in-situ PXRD during toluene vapour adsorption. The points on the adsorption and desorption isotherms correspond to the PXRD patterns shown in (d). Toluene uptake causes a phase transformation to the ip phase around p/p0 = 0.05. No further phase transformations are observed at higher toluene loading. The COF returns to the cp phase upon desorption of the solvent. In this COF, the PDIs are slip-stacked with 3.2 Å offset along the long molecular axis, which translates into a bridge-to-bridge distance of 4.2 Å.
