After Soxhlet extraction and de-intercalation, we detect no Li-and no Br-ions in combustion analysis and ICP-OES. The calculated composition of PTI-IF is C6.0H3.5N9.0 (Li wt% << 0.5) (theoretical C6H3N9). EELS shows no evidence of intercalated ions in the form of Li/Br Kedges at the microscopic level (Figure ). In addition, we performed X-ray photoelectron spectroscopy (XPS) measurements to quantify the C:N ratio at the surface of the PTI-LiBr films. We observe a C:N ratio of 41:59 at% (theoretical 40:60 at%) (Figure ). Overall, results of the macroscopic and microscopic composition analysis reflect a high material purity. The unit-cell of PTI-LiBr has been described in great detail, and it serves as point of reference for the structure refinement and solution of PTI-IF. We obtained a unit-cell for PTI-IF using powder X-ray diffraction (PXRD) (Figure , a), convergent beam electron diffraction (CBED) (Figure ), and structural optimization by density functional theory (DFT) (Figure ). The DFT-optimized unit-cell of PTI-IF agrees well with X-ray and electron diffraction data, and it indicates that intercalate-free PTI-sheets assume a corrugate arrangement.