Vinylene‐Linked Covalent Organic Frameworks (COFs) with Symmetry‐Tuned Polarity and Photocatalytic Activity

Abstract

Abstract The polarity of a semiconducting molecule affects its intrinsic photophysical properties, which can be tuned by varying the molecular geometry. Herein, we developed a D 3 h ‐symmetric tricyanomesitylene as a new monomer which could be reticulated into a vinylene‐linked covalent organic framework (g‐C 54 N 6 ‐COF) via Knoevenagel condensation with another D 3 h ‐symmetric monomer 2,4,6‐tris(4′‐formyl‐biphenyl‐4‐yl)‐1,3,5‐triazine. Replacing tricyanomesitylene with a C 2 v ‐symmetric 3,5‐dicyano‐2,4,6‐trimethylpyridine gave a less‐symmetric vinylene‐linked COF (g‐C 52 N 6 ‐COF). The octupolar conjugated characters of g‐C 54 N 6 ‐COF were reflected in its scarce solvatochromic effects either in ground or excited states, and endowed it with more promising semiconducting behavior as compared with g‐C 52 N 6 ‐COF, such as enhanced light‐harvesting and excellent photo‐induced charge generation and separation. Along with the matched energy level, g‐C 54 N 6 ‐COF enabled the two‐half reactions of photocatalytic water splitting with an average O 2 evolution rate of 51.0 μmol h −1 g −1 and H 2 evolution rate of 2518.9 μmol h −1 g −1 . Such values are among the highest of state‐of‐the‐art COF photocatalysts.