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

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 D3h‐symmetric tricyanomesitylene as a new monomer which could be reticulated into a vinylene‐linked covalent organic framework (g‐C54N6‐COF) via Knoevenagel condensation with another D3h‐symmetric monomer 2,4,6‐tris(4′‐formyl‐biphenyl‐4‐yl)‐1,3,5‐triazine. Replacing tricyanomesitylene with a C2v‐symmetric 3,5‐dicyano‐2,4,6‐trimethylpyridine gave a less‐symmetric vinylene‐linked COF (g‐C52N6‐COF). The octupolar conjugated characters of g‐C54N6‐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‐C52N6‐COF, such as enhanced light‐harvesting and excellent photo‐induced charge generation and separation. Along with the matched energy level, g‐C54N6‐COF enabled the two‐half reactions of photocatalytic water splitting with an average O2 evolution rate of 51.0 μmol h−1 g−1 and H2 evolution rate of 2518.9 μmol h−1 g−1. Such values are among the highest of state‐of‐the‐art COF photocatalysts.

Enormous Promotion of Photocatalytic Activity through the Use of Near-Single Layer Covalent Organic Frameworks

“…[1][2][3][4][5][6][7][8][9][10] Visible light responsive 2-D COFs, e.g. diacetylene functionalized COFs, 11 azine COF, 12 sp 2carbon-linked triazine-cored COFs, [13][14][15] thiazolo thiazole-linked COFs, hydrazone-based COFs and sulfonecontaining COFs, 18 have been synthesized and used for visible-light driven H 2 production. However, most of COFs show mediocre activity in photocatalytic H 2 evolution (PHE) compared with traditional inorganic semiconductors, which is mainly related to the difficulty in dissociation of excitons and the rapid recombination of photogenerated electrons and holes during photocatalytic process.…”

A 2D porphyrin-based covalent organic framework with TEMPO for cooperative photocatalysis in selective aerobic oxidation of sulfides

“…28 In 2014, Lotsch and co-workers reported the first example of utilizing 2D COFs for photocatalytic hydrogen evolution under visible-light irradiation. 29 Since then, their application in photocatalysis has received increasing attention, and 2D COFs have been realized as efficient catalysts in photocatalytic hydrogen evolution, [30][31][32][33] CO 2 reduction, [34][35][36] selective organic transformations 37,38 and dye degradation. 39,40 Among these tested reactions, photocatalytic selective organic transformations are very attractive as they can offer a simple but environment friendly and sustainable way to synthesize important chemicals.…”

Covalent organic frameworks with high quantum efficiency in photocatalytic hydrogen evolution: mediating charge separation

“…3d, Supplementary Table 5 and 6). [32][33][34][35][36][37][38][39][54][55][56][57][58][59][60][61][62][63][64][65][66] As compared with the reported COF/polymer-based photocatalyst, CN-CON showed the highest AQE as far as we know, which was in a comparable level to that of previously reported star inorganic Pt-PdS/CdS photocatalyst. [4] Even comparing with the H 2 evolution rate normalized by the mass, CN-CON is suprior to most of the COFs/polymer-based photocatalyst.…”

“…4a, 4c). [32,41,67] Further, based on a simple model, the temperature dependent PL intensity of two CONs can be expressed by the following equation:…”