Construction of Thiadiazole-Bridged sp²-Carbon-Conjugated Covalent Organic Frameworks with Diminished Excitation Binding Energy Toward Superior Photocatalysis

Abstract

Sp 2 -carbon-conjugated covalent organic frameworks (sp 2 c-COFs) have emerged as promising platforms for phototo−chemical energy conversion due to their tailorable optoelectronic properties, in-plane πconjugations, and robust structures. However, the development of sp 2 c-COFs in photocatalysis is still highly hindered by their limited linkage chemistry. Herein, we report a novel thiadiazole-bridged sp 2 c-COF (sp 2 c-COF-ST) synthesized by thiadiazole-mediated aldol-type polycondensation. The resultant sp 2 c-COF-ST demonstrates high chemical stability under strong acids and bases (12 M HCl or 12 M NaOH). The electrodeficient thiadiazole together with fully conjugated and planar skeleton endows sp 2 c-COF-ST with superior photoelectrochemical performance and charge-carrier separation and migration ability. As a result, when employed as a photocathode, sp 2 c-COF-ST exhibits a significant photocurrent up to ∼14.5 μA cm −2 at 0.3 V vs reversible hydrogen electrode (RHE) under visible-light irradiation (>420 nm), which is much higher than those analogous COFs with partial imine linkages (mix-COF-SNT ∼ 9.5 μA cm −2 ) and full imine linkages (imi-COF-SNNT ∼ 4.9 μA cm −2 ), emphasizing the importance of the structure−property relationships. Further temperature-dependent photoluminescence spectra and density functional theory calculations demonstrate that the sp 2 c-COF-ST has smaller exciton binding energy as well as effective mass in comparison to mix-COF-SNT and imi-COF-SNNT, which suggests that the sp 2 c-conjugated skeleton enhances the exciton dissociation and carrier migration under light irradiation. This work highlights the design and preparation of thiadiazole-bridged sp 2 c-COFs with promising photocatalytic performance.

Linkage‐Mediated Electronic Structure Modulation in Multicomponent Covalent Organic Frameworks for Dramatically Promoted Photocatalytic Hydrogen Evolution

“…Accordingly, the corresponding conduction band (CB) and valence band (VB) positions were determined, as depicted in Figure 3d. Given the more negative E CB values than the reduction potential of protons, these COFs can be considered as promising candidates to thermodynamically allow photoexcited electrons to reduce H + to hydrogen, [54] while the similar results for TT-PQCOF-CN and TT-PQCOFÀ F (Figures S17-S19). As this work focuses on the influence of continuous linkage-mediated electronic structure modulation on photocatalytic HER performance, the ultimate linkage protonation is considered as the key step to achieve the target COF photocatalysts.…”

Metal– and covalent organic frameworks for photocatalytic CO2reduction coupled with H2O oxidation

“…135,146 This design reduces the electron transport distance and mitigates the interfacial charge transport barrier, thereby enhancing the efficiency of the charge transport process within the material to a certain extent. 147,148 In addition, unlike multicomponent heterojunctions, porous COFs and MOFs generally have good mechanical stability. Different organic monomers can build COFs through strong covalent bonds ( e.g.…”

Delocalization Engineering of Heme‐Mimetic Artificial Enzymes for Augmented Reactive Oxygen Catalysis

“…Therefore, constructing new and more efficient heme-mimetic artificial enzymes for ROS biocatalytic applications is urgently needed in current biochemical and biomedical sciences. [14] Investigation on porous polymers in recent years have validated that the conjugated structure and coordination environment have a great impact on their catalytic performances, [15] but the related effects on ROS catalysis have not been studied, especially for the porphyrin-evolving artificial enzymes. Phthalocyanine can be recognized as the structural analogy with porphyrin in which the four methine bridge carbon atoms are replaced by nitrogen atoms, and the aromatic system is enlarged by adding four benzo rings, [16] and it shows good accessibility in terms of straightforward preparation on a large scale and outstanding electrocatalytic performance in the energy fields.…”