Extended Data Fig. 3: Structure analysis and solvent-induced phase transformations of the prPDI-1P COF.
(a) PXRD analysis of the dry prPDI-1P COF. Pawley refinement (red line) provides a very good fit to the PXRD data (black dots). Rwp = 5.8% (w/o background), Rp = 3.8%. Inset: Force-field optimised structure model of the COF. In this phase, 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). Apart from its negligible porosity, the dry prPDI-1P COF closely resembles the buPDI-1P COF ip phase where the alkyl chains are straight but arranged in a side-by-side configuration. Note: A fully contracted cp phase is not observed for this COF. (b) PXRD analysis of the toluene-loaded prPDI-1P COF. Pawley refinement (red line) provides a good fit to the PXRD data (black dots). Rwp = 18% (w/o background), Rp = 5.8%. 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) with a head-to-head arrangement of the alkyl chains that closely resembles the buPDI-1P COF op phase. The reflections at 6.5° and 11.1° are due to unreacted prPDI starting material (prPDI has very low solubility). (c,d) Solvent-induced structural transformations monitored by in-situ PXRD during toluene vapour adsorption. The points on the adsorption isotherm correspond to the PXRD patterns shown in (d). Toluene uptake causes a phase transformation to the op phase around p/p0 = 0.1. The last XRD pattern, collected under vacuum after solvent desorption, confirms the full reversibility of the phase transformation. The reflections at 6.5° and 11.1° are due to unreacted starting material. In this COF, the PDIs are slip-stacked with 3.1 Å offset along the long molecular axis, which translates into a bridge-to-bridge distance of 4.1 Å.
