It is well-known that, acylation or alkylation at the pyridyl nitrogen always leads to nucleophilic attack on the pyridine ring due to the strengthened electron deficiency . Alkylation at the pyridyl nitrogen has been verified to efficiently promote a Knoevenagel condensation at the pyridylmethyl carbon atoms . Considering that pyridine can act as Lewis base for catalyzing hydrolysis of acetic anhydride through the formation of the Nacetyl pyridinium ion intermediate , under our circumstance, the proposed mechanism could begin with the benzoylation of methylpyridine moieties by benzoic anhydride to give the benzoyl pyridinium salt. The electron-deficient character of pyridine ring was significantly increased by the benzoylation, thus favorable for the enhancement of C-H acidity on the pyridyl methyl. Meanwhile, the generated conjugated base benzoate also could capture the protons at the methyl groups, leading to the formation of enamine intermediate. Subsequently, electrophilic attack of the protonated aldehyde in the presence of benzoic acid, to the above The crystallinity of COF-DFB was examined by powder X-ray diffraction (PXRD) measurements. Theoretically, the condensation of a D2h monomer and a C2 monomer can give rise to two possible 2D COF structures, that is, an orthorhombic system that bears only a single-pore framework and a hexagonal system that possesses two different kinds of pores with Kagome lattice . Indexing of the PXRD pattern of COF-DFB identified the space group Cmmm (No. 65), indicating an orthorhombic lattice. The diffraction peaks at 5.81°, 11.67° and 25.90° could be assigned to (110), ( ) and (001) facets, respectively (Figure ). The experimental PXRD pattern of COF-DFB was in accordance with simulated pattern of a orthorhombic lattice with AA stacking mode, whereas the staggered AB stacking model and Kagome lattices exhibit significant difference from the experimental PXRD data (Figures and). The first dominant diffraction peak at 5.81° corresponds to the d-spacing of 1.52 nm, which was in good agreement with the calculated diameter of the rhombic pore (1.4 nm, Figure ). Fourier transform infrared (FT-IR) spectra of COF-DFB and COF-BPDA were analyzed by comparison with the monomer and the model molecule (Figure and Figure ). The disappearance of C-H vibration (2916 cm -1 ), attenuation of C=O stretching band (1694 cm -1 ) and appearance of new intensive vinyl (C=C) bands at 961 and 1631 cm -1 , confirmed the high polycondensation degree of COFs. These observations were further confirmed by the complementary Raman spectra analysis (Figure ), which showed the characteristic Raman signals at 1630 cm -1 for the C=C stretch vibration. The formation of vinyl-linked COFs was further verified by C cross-polarization magic angle spinning (CP-MAS) solidstate NMR spectroscopy, showing good match with the C NMR spectra of the model molecule (Figure and Figure ). The permanent porosity of COF-DFB and COF-BPDA was assessed by N2 sorption measurements at 77 K (Figure ). Both COFs show the reversible type I isotherms with rapid N2 uptakes at the low relative pressure range P/P0 < 0.05, characteristic of microporous materials. Brunauer-Emmett-Teller (BET) surface areas calculated from N2 adsorption isotherms revealed that the COF-DFB and COF-BPDA exhibited high specific surface areas of 1104 m 2 g -1 and 1560 m 2 g -1 , respectively. The pore size distribution analysis of COF-DFB and COF-BPDA based on the quenched solid density functional theory (QSDFT) indicates one main distribution centered at 1.40 nm and 1.70 nm, respectively, which is in consistent with the pore diameter based on the Conolly surface in their eclipsed (AA) layer stacking mode (Figures and). The morphologies and microstructures of the two COFs were studied by scanning electron microscopy (SEM) and Highresolution transmission electron microscopy (HRTEM). The SEM images show that COF-DFB and COF-BPDA are composed of layered blocks (Figures and). HRTEM images exhibit longrange ordered microstructures of the two COFs. The lattice fringes was clearly visualized in Figures and, suggesting the high crystallinities of these samples. One-dimensional channels with uniform distance of 1.40 nm and 1.70 nm for COF-DFB and COF-BPDA was clearly visualized along the [001] direction, corresponding to the d-spacing of (110) facet. Fast Fourier transform (FFT) of the raw HRTEM images generates a tetragonal arrangement of four white diffraction spots, corresponding to (110) facet (low right of Figures and). A rhombic porous structure can be observed on the HRTEM image of COF-BPDA, further indicating the formation of orthorhombic lattice, which is in accordance with the PXRD analysis (Figure ).