Abstract
Developing a facile strategy for the construction of vinylene-linked fully π-conjugated covalent organic frameworks (COFs) remains a huge challenge. Here, a versatile condition of Knoevenagel polycondensation for constructing vinylene-linked 2D COFs was explored. Three new examples of vinylene-linked 2D COFs (BTH-1, 2, 3) containing benzobisthiazoles units as functional groups were successfully prepared under this versatile and mild condition. The electron-deficient benzobisthiazole units and cyano-vinylene linkages were both integrated into the π conjugated COFs skeleton and acted as acceptor moieties. Interestingly, we found the construction of a highly ordered and conjugated D-A system is favorable for photocatalytic activity. BTH-3 with benzotrithiophene as the donor with a strong D-A effect exhibited an attractive photocatalytic HER of 15.1 mmol h−1g−1 under visible light irradiation.
Highlights
Developing a facile strategy for the construction of vinylene-linked fully π-conjugated covalent organic frameworks (COFs) remains a huge challenge
The cyano-vinylene-linked 2D COFs were mainly prepared via base-catalyzed Knoevenagel condensation condition[57]
Three fully sp2-carbon conjugated 2D COFs containing benzobisthiazole units as an electron-withdrawing group were successfully prepared via Knoevenagel polycondensation under this mild condition
Summary
Developing a facile strategy for the construction of vinylene-linked fully π-conjugated covalent organic frameworks (COFs) remains a huge challenge. A versatile condition of Knoevenagel polycondensation for constructing vinylene-linked 2D COFs was explored. Three new examples of vinylene-linked 2D COFs (BTH-1, 2, 3) containing benzobisthiazoles units as functional groups were successfully prepared under this versatile and mild condition. The construction of highly ordered structures of COFs mainly relies on the reversibility of dynamic covalent bonds between the building blocks. Three new fully sp2-carbon πconjugated COFs containing benzobisthiazole (BTH) as functional groups were constructed by Knoevenagel polycondensation under this new explored reaction condition. The integration of BTH unit and cyano-vinylene linkage provides an electron-deficient π-conjugated C2 symmetrical building block (Fig. 1) Other functional moieties such as triazine and benzotrithiophene were introduced as the C3 symmetrical units. Thanks to the extended π-electron conjugation and highly ordered D-A structure, BTH-3 with benzotrithiophene as electron-donor unit exhibited an attractive photocatalytic HER of 15.1 mmol h−1 g−1 under visible light irradiation
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