Xiaojia Zhao

Constitutional isomerism in conjugated covalent organic polymers reshapes network connectivity, and charge-transfer behavior, leading to markedly enhanced visible-light photocatalytic H ₂ O ₂ production.

Photocatalytic synthesis of H ₂ O ₂ from oxygen and/or water offers a sustainable alternative to conventional production routes but remains challenging for industrial application due to limited light harvesting and insufficient charge separation. Herein, two van der Waals heterojunctions were constructed by integrating ultrathin poly(triazine imide) (PTI) nanosheets with two structurally distinct covalent organic frameworks (COFs), giving rise to distinct interfacial growth behaviors for TTB‐COF and TTT‐COF on the PTI surface. Compared with the lateral (face‐to‐face) stacking in PTI‐TTT, the predominantly vertical interfacial contact in PTI‐TTB is associated with a more intimate interface, stronger internal electric field, and more abundant accessible active sites. As a result, the optimized PTI‐TTB delivers a superior H ₂ O ₂ production rate of 4402 μmol g ⁻¹ h ⁻¹ with an apparent quantum yield of 2.61% at 420 nm, which are 23.4 and 4.8 times higher than those of pristine PTI and TTB‐COF, respectively. Experimental results and density functional theory (DFT) calculations support that the superior photocatalytic performance is related to an efficient S‐scheme charge transfer pathway established at the strongly coupled interface. Mechanistic investigations further indicate that the synergistic coupling of the two‐electron oxygen reduction reaction (2e ⁻ ORR) and two‐electron water oxidation reaction (2e ⁻ WOR) accounts for the enhanced H ₂ O ₂ photosynthesis.

Constitutional isomerism in covalent organic frameworks (COFs) has shown promise for enhancing material properties, especially for photocatalytic applications. Herein, we design two isomeric multicomponent COFs (MC-COFs) via Schiff-base condensation followed by a Povarov reaction to convert the imine linkages into quinoline structures. These isomeric MC-COFs possess opposing C=N bond orientations and differently aligned phenyl groups within COF pores, leading to distinct torsion angles in COF layers. Structural analysis reveals that the enhanced planarity of COFs promotes π-π stacking and electron delocalization, resulting in a favorable band structure and reduced exciton binding energy. Consequently, the COFs achieve a superior hydrogen peroxide (H ₂ O ₂ ) production rate of 3128 µmol g ⁻¹ h ⁻¹ under visible light. This study underscores the critical influence of structural isomerism on the photocatalytic efficiency of MC-COFs and provides insights for optimizing COF-based photocatalytic systems.

Acidic electrochemical CO ₂ reduction reaction (eCO ₂ RR) offers a promising way for achieving high CO ₂ utilization efficiency and circumventing carbonate deposition issues. However, it is plagued by a compromised catalytic performance due to the severe hydrogen evolution reaction (HER). Here, two types of silver chalcogenolate cluster‐based MOFs were synthesized through ligand engineering by anchoring Ag ₁₂ clusters with tri‐topic imidazole and pyridyl ligands respectively. The imidazole‐based MOF Ag ₁₂ THIT demonstrated outstanding performance for the electroreduction of CO ₂ to CO. In acidic electrolyte of pH ≈ 2, it achieved a Faradaic efficiency (FE) of 98.5% with a commercial current density of 328.0 mA cm ⁻² at − 1.6 V versus RHE. Moreover, the CO partial current density ( j _CO ) reached a maximum of 447.2 mA cm ⁻² with a FE _CO of 96.8% at − 1.7 V versus RHE. No obvious degradation was observed during 70 h of continuous operation, and the performance significantly outperformed those of pyridyl‐based MOFs Ag ₁₂ TPEB and Ag ₁₂ TPMA . Mechanistic studies revealed that the imidazole ligand endows Ag ₁₂ THIT with enhanced Lewis basicity and superior σ ‐donating ability, thereby strengthening the ligand field with an upshifted d ‐band center and reduced energy barriers. This ligand effect facilitates more efficient electron transfer to *COOH intermediates, thus promoting acidic CO ₂ to CO conversion.

Acidic electrochemical CO ₂ reduction reaction (eCO ₂ RR) offers a promising way for achieving high CO ₂ utilization efficiency and circumventing carbonate deposition issues. However, it is plagued by a compromised catalytic performance due to the severe hydrogen evolution reaction (HER). Here, two types of silver chalcogenolate cluster‐based MOFs were synthesized through ligand engineering by anchoring Ag ₁₂ clusters with tri‐topic imidazole and pyridyl ligands respectively. The imidazole‐based MOF Ag ₁₂ THIT demonstrated outstanding performance for the electroreduction of CO ₂ to CO. In acidic electrolyte of pH ≈ 2, it achieved a Faradaic efficiency (FE) of 98.5% with a commercial current density of 328.0 mA cm ⁻² at − 1.6 V versus RHE. Moreover, the CO partial current density ( j _CO ) reached a maximum of 447.2 mA cm ⁻² with a FE _CO of 96.8% at − 1.7 V versus RHE. No obvious degradation was observed during 70 h of continuous operation, and the performance significantly outperformed those of pyridyl‐based MOFs Ag ₁₂ TPEB and Ag ₁₂ TPMA . Mechanistic studies revealed that the imidazole ligand endows Ag ₁₂ THIT with enhanced Lewis basicity and superior σ ‐donating ability, thereby strengthening the ligand field with an upshifted d ‐band center and reduced energy barriers. This ligand effect facilitates more efficient electron transfer to *COOH intermediates, thus promoting acidic CO ₂ to CO conversion.

The photocatalytic oxidative dipolar [3 + 2] cycloaddition reaction is a promising green approach for producing pyrrolo[2,1-a]isoquinolines. However, developing sustainable cycloaddition methods with heterogeneous photocatalysts is still in its infancy, largely owing to their low reactivity and photostability. Herein, we propose a charge–oxygen synergy strategy through a dual-engineered covalent organic framework (COF) by integrating π-spacers with donor–acceptor motifs to promote intermolecular cycloaddition. Systematic analyses reveal that electron-deficient thiadiazole units significantly enhance exciton dissociation efficiency, while a fully conjugated acetenyl spacer promotes spontaneous oxygen adsorption to stabilize endoperoxide intermediate species. This synergistic interplay between charge separation and oxygen activation significantly boosts reactive oxygen species generation, enabling efficient C–H bond activation under visible light. Remarkably, the BTDE-COF efficiently promotes dipolar [3 + 2] cycloaddition, achieving up to 97.1% yield with a broad substrate scope under visible light irradiation, while enabling a gram-scale synthesis. This work suggests that strategically engineering COFs has the potential to foster a variety of visible light-mediated energy-transfer processes.

The development of imine‐linked covalent organic frameworks (COFs) has also drawn attention to the influence of the nature of imine binding, including its orientation and possible protonation, on the chemical and physical properties of imine COFs. However, the influence of the polarity of imine bond (C═N) on the photocatalytic performance of COFs has not yet been described. In this work, we synthesized a series of imine COFs with differently polarized C═N bonds by altering the C═N bond orientation and regulating the donor–acceptor (D–A) strength, respectively. The less polarized C═N bond for one of the COFs possesses a faster charge separation with a decrease of exciton binding energy ( E _b ). In contrast, the imine COF with more polarized C═N bond exhibits a stronger internal electric field contributing to a more efficient charge transfer. Taking into account this trade‐off between binding energy and charge transfer concerning the effect of C═N polarity on the photocatalytic performances, the imine COF with moderately polarized C═N bond shows the highest hydrogen evolution performance of 14.0 mmol h ⁻¹  g ⁻¹ . This work provides evidence that the polarity of C═N should be taken into account when designing and tuning the properties of imine COFs.

The development of imine‐linked covalent organic frameworks (COFs) has also drawn attention to the influence of the nature of imine binding, including its orientation and possible protonation, on the chemical and physical properties of imine COFs. However, the influence of the polarity of imine bond (C═N) on the photocatalytic performance of COFs has not yet been described. In this work, we synthesized a series of imine COFs with differently polarized C═N bonds by altering the C═N bond orientation and regulating the donor–acceptor (D–A) strength, respectively. The less polarized C═N bond for one of the COFs possesses a faster charge separation with a decrease of exciton binding energy ( E _b ). In contrast, the imine COF with more polarized C═N bond exhibits a stronger internal electric field contributing to a more efficient charge transfer. Taking into account this trade‐off between binding energy and charge transfer concerning the effect of C═N polarity on the photocatalytic performances, the imine COF with moderately polarized C═N bond shows the highest hydrogen evolution performance of 14.0 mmol h ⁻¹  g ⁻¹ . This work provides evidence that the polarity of C═N should be taken into account when designing and tuning the properties of imine COFs.