Polymorphism in covalent organic frameworks (COFs) offers a unique platform to decipher structure-property relationships, yet its impact on excited-state dynamics remains unexplored. Herein, we construct two chemically identical but topologically distinct 1D and 2D COF polymorphs to correlate framework architecture with photocatalytic performance. Impressively, in H2O2 photosynthesis coupled with furfuryl alcohol valorization, the 1D-TBPP-COF showed an exceptional H2O2 generation rate (18.75 mmol g-1 h-1) and selective oxidation of furfuryl alcohol to high-value 6-hydroxy-2H-pyran-3(6H)-one (PN) with PN formation rate of 28.14 mmol·g-1·h-1, substantially outperforming the 2D-TBPP-COF counterpart. Mechanistic investigations revealed that the intercalated dual-chain edges in 1D-TBPP-COF impose steric constraints on aromatic ring rotation, effectively suppressing vibrational relaxation losses and prolonging the charge-transfer state lifetime. In contrast, the conformationally flexible 2D-TBPP-COF permits greater rotational freedom, leading to non-radiative energy dissipation. This work establishes polymorphism engineering as a powerful strategy to manipulate excited-state dynamics in COFs for photocatalysis.
Covalent organic frameworks (COFs) have attracted considerable attention as promising photocatalysts for hydrogen peroxide (H2O2) production. To further improve their catalytic performance, a quaternary ammonium functionality was introduced into the bipyridine units of the COF via a post-synthetic modification strategy. Under identical irradiation conditions, the cationized Pry-COF-QA achieved a H2O2 production rate of 7.31 mmol·h–1·g–1, which is markedly higher than that of the non-protonated Pry-COF (5.50 mmol·h–1·g–1). To gain mechanistic insight into the enhanced activity, density functional theory (DFT) calculations were performed. The results indicate that the incorporation of the quaternary ammonium group fundamentally reconfigures the photophysical behavior. In addition to inducing a red shift in the absorption spectrum by narrowing the HOMO–LUMO energy gap, it more importantly converts the excitation character from a localized excitation (LE) state, which is unfavorable for charge separation, to an intramolecular charge transfer (ICT) state with well-separated spatial distribution. This efficient ICT pathway effectively suppresses electron–hole recombination, thereby significantly prolonging the lifetime of photogenerated charge carriers and ultimately facilitating efficient photocatalytic H2O2 production, while also providing a valuable guideline for the rational design of COF-based systems toward efficient photocatalytic H2O2 generation.
Zhihui Sun, Jiajia Li, Long-Yang Yang et al.· ACS Applied Energy Materials· 0 citations
Covalent organic frameworks (COFs) are promising photocatalysts for solar-driven hydrogen evolution due to their tunable structures and intrinsic porosity. In this work, a series of Tp-Pa-based COFs bearing different electron-withdrawing groups was synthesized via a scalable mechanochemical route to examine the impact of framework functionalization on their structural, electronic, and photocatalytic properties. Spectroscopic analyses (solid-state 1 3C CP-MAS NMR and FT-IR) confirmed the formation of β-ketoenamine linkages, while PXRD revealed higher crystallinity for pristine Tp-Pa compared to its functionalized analogues. Electrochemical studies indicated n-type semiconducting behavior, with pristine Tp-Pa exhibiting more efficient charge separation and lower charge-transfer resistance. Under visible-light irradiation, Tp-Pa showed the highest hydrogen evolution rate (25,717 µmol g- 1 h- 1), whereas functionalized derivatives displayed reduced activity, with Tp-Pa-NO2 being nearly inactive. Notably, Tp-Pa also demonstrated excellent performance in simulated seawater (33,331 µmol g- 1 h- 1). These findings highlight the critical role of functionalization and synthesis strategy in governing crystallinity, charge transport, and photocatalytic efficiency, offering design guidelines for scalable COF-based hydrogen evolution systems.
Kiran Asokan, S. S. Babu· Chemistry - An Asian Journal· 0 citations
Covalent organic frameworks (COFs) provide a polymer platform for exploring covalent linkages to design ordered skeletal and porous architectures. However, the role of linkages in controlling structural and functional evolutions remains to be well explored. In this study, we reported hexaphenyltriphenylene COF photocatalysts constructed with ketazine or azine linkages that differ by a single pinpoint methyl substituent, enabling a controlled interrogation of linkage chemistry. Unexpectedly, the ketazine linkage enhances water uptake, accelerates transport, and directs water confinement within trigonal pores. Simultaneously, it modulates the π-electronic structure through hyperconjugation and inductive/resonance effects, extends light absorption, lowers exciton binding energy, prolongs charge-separated lifetimes, and promotes balanced charge transport. These synergistic structural and electronic evolutions translate into exceptional photocatalysis for hydrogen peroxide production from air and water under ambient conditions. Ketazine-HPTP-COF achieves a production rate of 8.17 mmol g-1 h-1 with an apparent quantum yield of 15.1% at 420 nm, outperforming azine-linked, amorphous, and other photocatalysts. The system operates under sunlight, enabling scalable production, and maintains activity across tap water, rainwater, and seawater. Mechanistic studies reveal dense yet spatially resolved photocatalytic sites, where linkage sites mediate oxygen reduction and knot units drive water oxidation, promoting photosynthesis through efficient charge and mass transport.
Yongzhi Chen, Xinyu Mu, Sailun Ji et al.· Angewandte Chemie· 1 citation
Solar-driven biomass valorization is pivotal for defossilizing the chemical industry. The oxidation of abundant, low-cost 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA)─a key monomer for next-generation bioplastics─is a long-sought goal yet hampered by sluggish kinetics, poor selectivity, and alkaline dependency. Here, spatially decoupled catalytic sites are engineered on two-dimensional carbon nitride (CN): covalently grafted cyanamide (CA) motifs at the edges and π-π stacked J-type nickel phthalocyanine (NiPc) dimers on the planes. This design features spatiotemporally cascaded charge transfer and dual-site catalysis, achieving 54- and 160-fold enhancements in the HMF conversion rate and H2 evolution rate, respectively, versus pristine CN, during HMF reforming in pure water. The FDCA production rate reaches 2.14 mmol g-1 h-1 with 98.2% selectivity, outperforming benchmark systems. Fundamentally, CA motifs steer an ultrafast hole-initiated selective HMF oxidation with a hole transfer rate of 2.4 × 1010 s-1 (an order of magnitude faster than CN). The resulting long-lived electrons are extracted by the bottom-layer NiPc and transferred via its single Ni atom to the top-layer single Ni atom for proton reduction, with an electron transfer rate of 7.4 × 104 s-1. The asymmetric charge kinetics suppresses charge recombination, yielding a charge transfer efficiency of 98.9%.
Xiaomeng Zhao, Jianhui Sun, Linlu Bai et al.· Journal of the American Chem...· 0 citations
Covalent organic frameworks (COFs) have emerged as promising candidates for singlet oxygen (
1
O
2
) generation via peroxymonosulfate (PMS) activation, yet their structure-property-activity relationships remain poorly understood. Herein, three constitutionally isomeric donor-acceptor COFs (TF-22Bpy, TA-22Bpy and TA-33Bpy) were constructed via N-site isomeric engineering, which involved precisely modulation of the imine and pyridine nitrogen positions within the skeleton. This systematically structural engineering was undertaken to unravel the fundamental effects of regioisomerism on both the electronic structure and subsequent Fenton-like catalytic activity. Among the isomers, TA-33Bpy showed the best catalytic activity for PMS activation, exhibiting an observed rate constant (
k
obs
) of 0.165 min
−1
. This value is substantially higher than those of TF-22Bpy (0.013 min
−1
) and TA-22Bpy (0.052 min
−1
) by factors of 12.7 and 3.2, respectively. Mechanistic investigations indicate that direct PMS-COF interaction induces charge polarization within the donor-acceptor framework, generating localized electron-deficient and electron-enriched domains that promote the coupled redox steps required for selective ¹O₂ generation. This work identifies PMS-triggered charge polarization as a key determinant of PMS activation and offers a design principle for high-performance COF catalysts for water purification.
Chengming Xiao, Meng-Ting He, Wenbo Yang et al.· Nature Communications· 0 citations
Covalent organic frameworks (COFs) hold promises for overall H2O2 photosynthesis. However, their efficiency is constrained by rapid charge recombination at the universal C=N linkages due to the nitrogen lone pairs acting as efficient hole traps. Here, we report a molecular-level electronic isolation strategy through the rational incorporation of C=N–N motifs into the COF backbone. This built-in energetic barrier effectively localizes electron density and directs charge flow along a preferential pathway, which collectively stabilizes the non-equilibrium charge-separated state and suppresses interfacial recombination. The resulting prolonged carrier lifetime enables efficient multi-electron overall H2O2 photosynthesis. Simultaneously, the molecular partition creates a spatially synergistic catalytic interface, which facilitates dual-site activation, promotes reactant adsorption and polarization, and significantly lowers the reaction energy barrier. In pure water and without sacrificial agents, the optimized TMN-COF achieves a H2O2 production rate of 4080 μmol g–1 h–1 with a solar-to-chemical conversion efficiency of 2.17% and sustains a production rate of 1330 μmol g–1 h–1 under ambient air conditions. When scaled up, the material retains catalytic activity (8.1 mmol L–1) and demonstrates broad-spectrum antimicrobial efficacy and efficient degradation of organic pollutants under visible-light irradiation. This work provides a foundational blueprint for spatially engineering interface charge behavior in COF photocatalysts.
Ziling Li, Zihe Wang, Donghui Lan et al.· ACS Catalysis· 0 citations