The crystalline structure of NKCOF-62 was resolved by powder X-ray diffraction (PXRD) measurements and computational simulation. DFT-based geometry optimizations were performed with the CP2K software package. The CP2K input file in this work was generated with the help of the Multiwfn program. As shown in Figure , the existence of high diffraction peaks in the PXRD pattern indicated that NKCOF-62 had a long-range ordered structure and crystalline nature, and three main diffraction peaks at 6.64°, 13.49° and 24.88° were assigned to (110), ( ) and (001) crystal facets, respectively. Pawley refinements were performed with the data from the experimental PXRD pattern to yield orthorhombic unit cell parameters of a=18.65 Å, b=18.71 Å, c=3.45 Å, α = γ = β = 90° (residuals R p = 0.81%, R wp = 1.07%). Eclipsed (AA) stacking mode was constructed with the above unit cell parameter to generate corresponding diffraction patterns for comparison with experimental data, which agreed well with the simulated AA stacking model. Notably, similar PXRD patterns are common in olefin-linked COFs due to their irreversible C=C bond nature. Various characterization approaches were employed to confirm the chemical component and structure of NKCOF-62. Fourier transform infrared spectra (FT-IR) showed a new characteristic absorbance at 962 and 1626 cm -1 , confirming the formation of the C=C bonds. The stretching vibration peak for methyl C-H of TMP monomer around 3000 cm -1 disappeared, and the stretching vibration peak for C=O of DFB monomer attenuated in the NKCOF-62, indicating their high polymerization degrees (Figure ). Comparing the C solid-state nuclear magnetic resonance (NMR) spectrum of NKCOF-62 with the liquid C NMR spectra of the model compound indicated that these signals well matched the corresponding carbon atoms. The carbonyl signals at around 123 and 136 ppm were typically arising from the olefin (C=C) carbon (Figure ), which further confirmed the formation of the olefin-linked COF. Scanning electron microscopy (SEM) image exhibited that NKCOF-62 was irregular morphology of the stacked blocks in the micro level. (Figure ). High-resolution transmission electron microscopy images (HR-TEM, Talos F200X G2) of NKCOF-62 revealed the significant crystal lattice, and the lattice fringe spacing was about 0.34 nm, which corresponded to the (001) facet (Figure ). Thermogravimetric analysis (TGA) showed excellent thermal stability of NKCOF-62 (Figure ), and there was no obvious weight loss up to 400 ℃ under N 2 atmosphere. In addition, the high chemical stability of NKCOF-62 was further investigated under different conditions, including boiling water, sodium hydroxide (NaOH, 10 M), and hydrochloric acid (HCl, 12 M). After soaking in the above solutions for 7 days, the crystallinity and skeletal structures were almost unchanged, as verified by FT-IR and PXRD (Figure N 2 adsorption isotherm was conducted at 77 K to evaluate the permanent porosity of NKCOF-62. As shown in Figure , NKCOF-62 showed a type I sorption isotherm, confirming its microporous structure. The Brunauer-Emmett-Teller (BET) surface area was calculated to be 654 m 2 /g, and the total pore volume was 0.59 cm 3 /g. Nonlinear density functional theory (NLDFT) cylindrical pore model-based pore size distribution analysis revealed a prominent pore size distribution profile centered at 0.7 nm, which was close to the calculated pore size (0.8 nm) for the eclipsed AA layer stacking model. Notably, NKCOF-62 possesses the smallest eclipsed pore among all orthorhombic 2D COFs (Figure ).