Two 2D covalent organic frameworks (COFs) linked by vinylene (-CH=CH-) groups (V-COF-1 and V-COF-2) are synthesized by exploiting the electron deficient nature of the aromatic s-triazine unit of C3 -symmetric 2,4,6-trimethyl-s-triazine (TMT). The acidic terminal methyl hydrogens of TMT can easily be abstracted by a base, resulting in a stabilized carbanion, which further undergoes aldol condensation with multitopic aryl aldehydes to be reticulated into extended crystalline frameworks (V-COFs). Both V-COF-1 (with terepthalaldehyde (TA)) and V-COF-2 (with 1,3,5-tris(p-formylphenyl)benzene (TFPB)) are polycrystalline and exhibit permanent porosity and BET surface areas of 1341 m2 g-1 and 627 m2 g-1 , respectively. Owing to the close proximity (3.52 Å) of the pre-organized vinylene linkages within adjacent 2D layers stacked in eclipsed fashion, [2+2] photo-cycloadditon in V-COF-1 formed covalent crosslinks between the COF layers.
Keywords: [2+2] cycloaddition; covalent organic frameworks; porous polymers; vinylene links; π⋅⋅⋅π stacking.
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.