Vinylene‐Linked Covalent Organic Frameworks (COFs) with Symmetry‐Tuned Polarity and Photocatalytic Activity
Junsong Xu, Can Yang, Shuai Bi, Wenyan Wang, Yafei He, Dongqing Wu, Qifeng Liang, Xinchen Wang, Fan Zhang
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.