Photocatalytic four-component reaction to access covalent organic frameworks for photocatalysis

Domain: chemistry
Published: 2026-02-21
Editorial outcome: major_revision

Abstract
Photocatalytic four-component reaction is an efficient and environmentally friendly synthetic strategy known for its step economy and operational simplicity, enabling the preparation of diverse organic products. However, its application in synthesizing covalent organic frameworks (COFs) remains unexplored. Here, we report the rational synthesis of a class of functionalized COFs with high crystallinity and permanent porosity via the photocatalytic four-component reaction. This strategy not only addresses the long-standing challenge of harsh reaction conditions in conventional COFs synthesis methods, but also enables the integration of four different types of monomers in a one-pot process to create structurally diverse COFs. Furthermore, the resulting Cp-tBu-N3-COF can function as an efficient photocatalyst for the visible-light-driven synthesis of benzimidazoles. This work provides a promising strategy to access COFs in a mild and sustainable way.

Introduction
Covalent organic frameworks (COFs) are a class of crystalline, porous organic polymers with highly ordered and extended structures, known for their intriguing properties of tunable pore size, large surface area, high chemical stability, and easy recyclability1–7. Since Yaghi et al. reported the synthesis of COFs in 20058, considerable progress has been made in their synthesis over the past 20 years9–14. However, most of the reported methods rely on relatively harsh reaction conditions, such as high temperature and pressure, underscoring the need for novel strategies to prepare COFs under mild conditions.

Visible-light photoredox catalysis has emerged as a powerful approach in synthetic chemistry for the synthesis of complex molecules from simple starting materials because of its mildness, low-energy consumption, and environmental friendliness15–20. Its versatility has also been demonstrated in providing alternative routes for the construction of COFs. Compared with the conventional methods for COFs synthesis, photoredox catalysis enables the formation of COFs under mild reaction conditions, while only a few examples have been reported thus far21–24. Research on the photocatalytic synthesis of COFs is still in the early stage, and its potential remains largely unexploited. Therefore, it is highly desirable yet challenging to explore more photocatalytic reactions to provide more possibilities in the design and preparation of COFs.

Multicomponent reactions (MCRs), which involve the one-pot combination of at least three substrates to form multiple new bonds without separating intermediates, are recognized as powerful tools in synthetic chemistry25,26. These reactions are valued for their convenient operation, high efficiency, and structural diversity. Recently, different types of MCRs, particularly three-component reactions such as Debus−Radziszewski reaction, Strecker reaction, Povarov reaction, and thiazole formation reaction, have been successfully applied to construct various COFs27–37. Despite these advances, the extension to four-component reactions (4CRs)38 for COFs synthesis remains largely unexplored, primarily due to the significantly increased complexity in controlling regio- and chemoselectivity. To date, Wang and co-workers reported the only case of the synthesis of functionalized COFs via the 4CRs using the solvothermal method39, which represents a major advancement in this field. This achievement highlights the potential of 4CRs to assemble four distinct monomers in a one-pot process, enabling the construction of structurally diverse COFs. When comparing various synthetic strategies, although the conventional two-component method is operationally simple and straightforward, it has fundamental limitations in terms of structural complexity and functional integration. The three-component reaction can offer improved structural diversity, yet remains constrained by relatively limited combinations of building blocks. In contrast, 4CRs offer a greater variety of combinatorial possibilities and allow precise integration of multiple functional groups within a single framework. The development of 4CRs systems will not only broaden the structural diversity of COFs, but also promote the advancement of their applications.

Given the immense potential of both 4CRs and photocatalysis, we propose integrating these two strategies to synthesize functionalized COFs via a photocatalytic four-component reaction—an approach that has yet to be explored. The merger of 4CRs with visible-light photoredox catalysis to synthesize functionalized COFs represents a significant advancement in the field of porous material synthesis. Firstly, it fully exploited the significant potential of the four-component reactions in achieving structural diversity and functional integration. Secondly, the implementation of photocatalytic technology effectively overcomes the limitations imposed by the conventional harsh reaction conditions. Finally, this photocatalytic four-component reaction strategy will open up new avenues for constructing COFs that are otherwise inaccessible through conventional methods.

Herein, we introduce a photocatalytic four-component reaction strategy for COFs synthesis at room temperature. Under visible-light irradiation, a series of COFs with high crystallinity and permanent porosity are successfully constructed via the photocatalytic four-component reaction of aromatic aldehydes, hydrazines, aromatic olefins, and boronic acids, using 4CzIPN as the photocatalyst. Furthermore, the obtained Cp-tBu-N3-COF exhibits good photocatalytic activity in the visible-light-driven condensation-cyclization reaction to afford various benzimidazoles, which are valuable heterocyclic structures valued for their diverse pharmacological and biological activities. This clean-energy-triggered approach not only offers a solution to the problem of harsh conditions in traditional synthetic methods but also allows the precise synthesis of structurally diverse COFs through the one-pot integration of four different types of monomers.

Results
Synthesis of Cp-tBu-N3-COF
As illustrated in Fig. 1a, the model reaction involving aniline, benzaldehyde, 4-tert-butylstyrene, and cyclopentylboronic acid successfully produced the model compound of M in 87% yield (Supplementary Figs. 2, 3)40. Based on this, we performed the photocatalytic four-component reaction by condensing four types of monomers, including 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (TFTP), hydrazine (HZ), 4-tert-butylstyrene (tBs), and cyclopentylboronic acid (CpBa). The synthetic conditions were systematically optimized by screening key parameters, including the acid, solvent, photocatalyst, light source, gas atmosphere, and reaction time (Supplementary Figs. 4–7). The optimized conditions were determined as crystallization in 1,4-dioxane/n-BuOH/DMA mixture (1.5:0.5:0.3, v/v/v) with acetic acid as the catalyst and 4CzIPN as the photocatalyst, under visible-light irradiation at room temperature for 72 h. Under the optimized conditions, the Cp-tBu-N3-COF was obtained as a yellow solid in 72% yield (Fig. 1b).

Characterization of COFs
Fourier transform infrared (FT-IR) spectroscopy, 13C CP-MAS solid-state NMR, and X-ray photoelectron spectroscopy (XPS) were employed to confirm the formation of Cp-tBu-N3-COF. In the FT-IR spectra of Cp-tBu-N3-COF, the characteristic peaks of 1704 cm−1 for C=O and 3356 cm−1 for N-H were strongly diminished after polymerization (Supplementary Fig. 8). In addition, compared to the pristine imine-based N3-COF41, the peak at approximately 1622 cm−1 corresponding to the C=N stretch was strongly attenuated, while new peaks appeared at 2864 and 2908 cm−1, associated with the cyclopentyl species, and at 2955 cm−1, corresponding to the tert-butyl group (Fig. 2a), indicating the successful formation of Cp-tBu-N3-COF. In the 13C CP-MAS solid-state NMR spectrum of Cp-tBu-N3-COF, resonance signals at 67, 31 and 25 ppm were observed, assigned to the carbons in C-NH, tert-butyl, and cyclopentyl moieties, respectively (Fig. 2b). Compared with N3-COF, the signal at 162 ppm corresponding to the imine carbon was significantly weakened, which provided solid evidence for the successful conversion of the imine linkage (Supplementary Fig. 9). XPS analysis further validated the chemical states of linked N atoms in Cp-tBu-N3-COF (Supplementary Fig. 10), revealing N 1s peaks at 398.9 and 398.2 eV, which are attributed to nitrogen in the C-NH bond and nitrogen in the triazine ring, respectively. All the spectral data are consistent with previous literature22,39 and the model compound (Supplementary Figs. 2, 3), confirming the successful synthesis of Cp-tBu-N3-COF.

As shown in Fig. 2c, the powder X-ray diffraction (PXRD) analysis indicates that the obtained Cp-tBu-N3-COF is a highly crystalline material. The PXRD pattern features a series of peaks at 3.52°, 6.14°, 7.10°, and 9.40°, which can be attributed to the reflections of (100), (110), (200), and (210) planes, respectively. The PXRD pattern of Cp-tBu-N3-COF was simulated utilizing the software of Materials Studio (ver. 2018), indicating a 2D eclipsed (AA) stacking mode. This assignment was further confirmed by Pawley refinement, which showed good agreement between the simulated and experimental patterns. The Cp-tBu-N3-COF is assigned to the space group P6, with the optimized parameters of a=b=28.68 Å, c=6.10 Å, α=β=90°, γ=120°, residuals Rwp = 4.40%, and Rp = 3.32%. Based on crystal structure analysis, the eclipsed 2D structure of Cp-tBu-N3-COF contains hexagonal pores (d = ca. 1.4 nm) with an interlayer distance determined as ca. 6.10 Å (Fig. 2d).

The porosity of Cp-tBu-N3-COF was analyzed using N2 adsorption-desorption measurements at 77 K (Fig. 3a). The Brunauer-Emmett-Teller (BET) surface area was determined to be 392 m2 g−1, with a total pore volume (P/P0 = 0.99) of 0.28 cm3 g−1. The pore size distribution, calculated using nonlocal density functional theory (NLDFT), revealed an average pore width of ~1.35 nm. This value agrees well with the pore size calculated from the simulated crystal structure, further confirming the validity of the simulated structure for Cp-tBu-N3-COF. In addition, scanning electron microscopy (SEM) was employed to observe the morphology of Cp-tBu-N3-COF, which showed a micrometer-scale particle morphology (Supplementary Fig. 11). The high-resolution transmission electron microscopy (HRTEM) image of Cp-tBu-N3-COF clearly showed the ordered crystalline lattice fringes with an interplanar distance of 0.61 nm (Supplementary Fig. 11), which agreed well with the vertical interlayer spacing of the simulated models. These results confirmed the highly crystalline and ordered porous structure of Cp-tBu-N3-COF.

The thermal stability of Cp-tBu-N3-COF was evaluated using thermogravimetric analysis (TGA), which revealed that the material remains stable up to 200 °C (Fig. 3b). Furthermore, in situ variable-temperature PXRD patterns for Cp-tBu-N3-COF were measured. The peaks remained unchanged before 200 °C (Supplementary Fig. 12), indicating no thermal degradation of the crystalline structure within this temperature range, which was also consistent with the TGA results. Subsequently, its chemical stability was further assessed by immersing it in 6 M sodium hydroxide (NaOH), 6 M hydrochloric acid (HCl), or ethanol (EtOH) for 3 days. The PXRD patterns and FT-IR spectra recorded after treatment remained almost identical to those of the pristine Cp-tBu-N3-COF, confirming its good chemical stability. Furthermore, Cp-tBu-N3-COF was found to be stable under blue LEDs irradiation, ensuring its suitability and reliability for photocatalysis (Fig. 3c, d).

The absorption property and energy levels of Cp-tBu-N3-COF were determined by the solid-state UV-vis diffuse reflectance spectrum and Mott–Schottky measurement (Fig. 4). The solid-state UV-vis diffuse reflectance spectrum of Cp-tBu-N3-COF displayed a broad absorption band extending up to 450 nm (Fig. 4a). The optical band gap (Eg) calculated from the Tauc plots was 2.80 eV (Fig. 4b), indicating its semiconductor characteristics. The positive slopes of the Mott–Schottky plots suggested that Cp-tBu-N3-COF was a kind of n-type semiconductor (Fig. 4c). The flat band of Cp-tBu-N3-COF was 0.04 V vs. RHE, and the conduction band (CB) was 0.04 V vs. RHE. Integrating the optical band gap and CB potential, the valence band (VB) was determined to be 2.84 V vs. RHE (Fig. 4d). Because the CB of Cp-tBu-N3-COF is more negative than the reduction potential of O2/O2•− (0.12 V vs. RHE), it can thermodynamically drive photocatalytic organic transformations mediated by O2•−. Furthermore, the electrochemical impedance spectroscopy (EIS) and photocurrent response were also investigated (Supplementary Fig. 13). Cp-tBu-N3-COF exhibited a small Nyquist radius and strong transient photocurrent response, indicating its small charge-transfer resistance and high photogenerated carriers transport efficiency. All the obtained results demonstrated that Cp-tBu-N3-COF could act as a promising photocatalyst.

Photocatalytic activity of Cp-tBu-N3-COF
Benzimidazole derivatives are important heterocyclic organic compounds with notable pharmacological and biological activities42. Their synthesis was chosen as a probe reaction to evaluate the photocatalytic performance of the synthesized Cp-tBu-N3-COF. The photocatalytic oxidative cyclization of o-phenylenediamine (1a) and benzaldehyde (2a) served as a model reaction. When a mixture of the substrates and a catalytic amount of Cp-tBu-N3-COF in acetone was irradiated by blue LEDs (λ = 440 nm) in air at room temperature for 8 h, the desired product, 2-phenylbenzimidazole (3a), was obtained in 26% yield (Table 1, entry 1). The effect of different solvents on the reaction yield was investigated, and EtOH was identified as the optimal solvent, affording 3a in a high yield of 97% (Table 1, entries 2–6). Screening of photocatalyst loading showed that 6 mg of Cp-tBu-N3-COF was optimal to yield 3a in 97% (Table 1, entries 6–8). When irradiated by LEDs of different wavelengths (Table 1, entries 9 and 10), no improvement in yield was observed compared to blue LEDs. Furthermore, the photocatalytic activity of Cp-tBu-N3-COF was competitive with that of most of the reported heterogeneous photocatalysts for this reaction (Supplementary Table 2). The photocatalytic activity of Cp-tBu-N3-COF was further quantified, with an apparent quantum yield (AQY) of 0.46% and a turnover frequency (TOF) of 4.39 h⁻¹ (performed once). Control experiments conducted without Cp-tBu-N3-COF, visible light, or oxygen resulted in only trace amounts of product, highlighting their indispensable roles in the catalytic system (Table 1, entries 11–13). Thus, the optimized conditions for this reaction were determined to be: 0.2 mmol of 1a, 0.2 mmol of 2a, and 6 mg of Cp-tBu-N3-COF in 2 mL of EtOH, irradiated with blue LEDs (λ = 440 nm) in air for 8 h at room temperature (Table 1, entry 6).

The leaching test shows that Cp-tBu-N3-COF is a typical heterogeneous catalyst (Fig. 5a). As reusability of a photocatalyst in heterogeneous reactions is a prime merit for industrial applications, a recycling experiment was conducted, and the yield of 3a remained as high as 95% even after five catalytic cycles (Fig. 5b). Moreover, the PXRD patterns and FT-IR spectra of Cp-tBu-N3-COF before and after five cycles are almost identical, indicating that its crystallinity and chemical structure were largely preserved (Fig. 5c, d). These results demonstrate that Cp-tBu-N3-COF has good photocatalytic performance and recyclability, making it a promising photocatalyst in photocatalysis.

With the optimal reaction conditions established, we further explored the scope of the benzimidazole formation reaction, as summarized in Table 2. A series of aromatic aldehydes with electron-donating or electron-withdrawing substituents were efficiently converted to substituted benzimidazoles in good yields, albeit some steric hindrance effect (3a–3n). Heterocyclic aldehydes, including 4-pyridinecarboxaldehyde and thiophene-3-carbaldehyde also performed well, yielding the corresponding benzimidazoles in 88% and 86% yields, respectively (3o–3p). In addition, the aliphatic substrate cyclohexanecarboxaldehyde was found to be highly effective, affording the product in 90% yield (3q). Similarly, various aromatic diamines bearing the substituents (–F, –Cl, and –Me) on the phenyl ring were converted to the desired benzimidazoles in high yields (3r–3u).

The photocatalytic process was significantly hindered under a nitrogen atmosphere, highlighting the crucial role of oxygen in the reaction (Table 1, entry 13). It is hypothesized that O2•− plays a key role in this photocatalytic process. To confirm the presence of reactive oxygen species during the reaction, a series of controlled experiments were conducted. p-Benzoquinone and NaN3 were added to the reaction system as capturing agents for O2•− and 1O2, respectively. The introduction of p-benzoquinone resulted in a sharp decrease of the yield from 97% to 26%, while NaN3 only slightly reduced the yield (Table 1, entries 14 and 15), suggesting that O2•− was the important intermediate in this photocatalytic reaction, rather than 1O2. Furthermore, electron-spin resonance (ESR) experiments were conducted using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as an O2•− scavenger. The characteristic signal of O2•− captured by DMPO was clearly observed after irradiation with the blue LEDs (Supplementary Fig. 15), providing direct evidence of the involvement of O2•− in the transformation. Furthermore, density functional theory (DFT) computations were applied to visualize the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the segment of Cp-tBu-N3-COF (Supplementary Fig. 16 and Supplementary Data 1). The HOMO and LUMO of the segment are mainly located at the hydrazine unit and the triazine moiety, respectively, suggesting the possibility of intramolecular charge transfer (ICT) within the framework, which may facilitate a single-electron transfer process. These computational results are thus consistent with the observed ability of Cp-tBu-N3-COF to generate superoxide anion radicals (O2•−) from triplet oxygen under visible light irradiation. The DFT method is inherently limited by the static nature of the simulations, which cannot fully capture the dynamic behavior under actual photocatalytic conditions.

Based on the above findings and previous reports43,44, a possible reaction mechanism is proposed (Fig. 6). Initially, 1a reacts with 2a via a Shiff-base reaction to form the imine intermediate I, which undergoes intramolecular cyclization to form intermediate II. At the same time, Cp-tBu-N3-COF reaches its excited state, Cp-tBu-N3-COF*, upon irradiation by visible light. This excited state is reductively quenched by intermediate II via a single electron transfer process to generate intermediate III and Cp-tBu-N3-COF•−. Subsequently, Cp-tBu-N3-COF•− is oxidized by molecular oxygen to produce O2•−, accompanied by the regeneration of Cp-tBu-N3-COF. Finally, the deprotonation and dehydrogenation of intermediate III assisted by O2•− affords the desired benzimidazole product 3a, and H2O2 as a byproduct.

The generality of this methodology for COFs synthesis
To further demonstrate the effectiveness and versatility of the photocatalytic four-component reaction in constructing functionalized COFs, we synthesized three additional COFs, including Cy-tBu-N3-COF, Cy-OMe-N3-COF and Cp-F-N3-COF, using other different monomers under the same synthetic conditions (Fig. 1b and Supplementary Figs. 17–46).

Methods
Instruments and materials
1H NMR spectra were recorded using a Bruker Avance 400 HD spectrometer with tetramethylsilane (TMS) as an internal standard. Mass spectra were obtained by a Bruker maxis ultra-high resolution-TOF MS system. ¹³C CP-MAS NMR measurements were carried out at 100.38 MHz with an 8 kHz spin rate on a 4 mm MAS probe. A Bruker ALPHA spectrometer was used to acquire FT-IR spectra between 400 and 4000 cm⁻¹. Thermal stability was assessed by TGA using a TA Instruments Q5 analyzer, with samples heated from 30 to 800 °C at 10 °C/min in an atmosphere of nitrogen. PXRD patterns was obtained on D8 Advance X-ray powder diffractometer with Cu Kα radiation (λ = 1.5405 Å). In situ variable-temperature PXRD patterns were measured on a PANalytical Empyrean 3 diffractometer equipped with Cu Kα radiation operating at 45 kV and 40 mA with the temperature ranging from 25 °C to 250 °C and a heating rate of 5 °C/min under vacuum. N2 adsorption measurements were carried out at 77 K with an ASAP 2020/TriStar 3000 (Micromeritics) analyzer. A Gemini Zeiss SupraTM scanning electron microscope, fitted with an EDX detector, was used to obtain SEM micrographs. A JEOL 2100 electron microscope operating at 200 kV was employed for high-resolution transmission electron microscopy (HRTEM) analysis. Solid-state UV-vis spectra were recorded on a Cary 5000 UV-Vis spectrophotometer (Varian, USA). Mott-Schottky, EIS and photocurrent measurements were performed on a CHI 660E electrochemical workstation with a standard three-electrode system. High-resolution mass spectrometry (HRMS) analysis was detected by Bruker maXis ultra high-resolution-TOF mass spectrometer. X-ray photoelectron spectroscopy (XPS) was performed using an ESCALAB 250 X-ray photoelectron spectrometer with a monochromatized Al Kα X-ray source (1486.71 eV). Electron paramagnetic resonance (EPR) spectra were measured by Bruker A300 EPR Spectroscopy. Irradiation with blue light was performed using Tao Yuan LED (5 W, λ = 440 nm, 145 lm @ 700 mA). The light intensity was measured by the TES-132 Solar Power Meter to be 200 mW cm−2. There are four blue LED lamps in each hole, which are used to irradiate the reaction tube. The material of the reaction tube is common glass, and the distance from the light source is about 0.5 cm. The blue light can penetrate the reaction vessel evenly with the same intensity45,46.

2,4,6-Tris(4-formylphenyl)-1,3,5-triazine (98.0%), 4-tert-butylstyrene (98.0%), 4-methoxystyrene (99.0%), 4-fluorostyrene (97.0%), cyclopentylboronic acid (97.0%), cyclohexylboronic acid (97.0%), benzaldehyde (99.0%), aniline (99.5%), 4CzIPN (99.0%), eosin-Y (80.0%), tris(2,2’-bipyridine)ruthenium(II) hexafluorophosphate (98.0%), (4,4’-di-tert-butyl-2,2’-bipyridine)bis[(2-pyridinyl)phenyl]iridium(III) hexafluorophosphate (97.0%), sodium sulfate (99.9%), potassium chloride (99.9%), 4-benzoquinone (99.5%), potassium hexacyanoferrate(II) (98.0%), potassium ferricyanide (99.5%), 5,5-dimethyl-1-pyrroline N-oxide (99.0%), o-phenylenediamine (98.0%), 3,4-diaminotoluene (98.0%), 4-chloro-o-phenylenediamine (97.0%), 4,5-difluoro-1,2-phenylenediamine (99.0%), 4-anisaldehyde (99.0%), 4-tert-butylbenzaldehyde (97.0%), 4-methyl benzaldehyde (98.0%), 2-methylbenzaldehyde (98.0%), 2-chlorobenzaldehyde (99.0%), 2-bromobenzaldehyde (98.0%), 4-fluorobenzaldehyde (98.0%), 4-chlorobenzaldehyde (98.0%), 4-bromobenzaldehyde (99.0%), 3-bromobenzaldehyde (97.0%), 4-hydroxybenzaldehyde (98.0%), methyl 4-formylbenzoate (98.0%), 1-naphthaldehyde (95.0%), 4-pyridinecarboxaldehyde (99.5%), 3-thiophenecarboxaldehyde (98.0%), cyclohexanecarboxaldehyde (97.0%) were purchased from Macklin Biochemical Co., Ltd. Acetic acid (99.8%), 1,4-dioxane (99.5%), n-butanol (99.5%), N,N-dimethylacetamide (99.5%), tetrahydrofuran (99.5%), acetone (99.5%), dichloromethane (99.5%), methanol (99.5%), ethanol (99.5%), mesitylene (99.5%), 1,2-dichlorobenzene (99.0%), HCl (36.0~38.0%), NaOH (98.0%), acetonitrile (99.5%), acetonitrile (99.5%), acetonitrile (99.5%) were purchased from Sinopharm Chemical Reagent Co., Ltd. Nafion solution (5%) and sodium azide (99.5%) were purchased from Sigma-Aldrich. All the chemicals were obtained from commercial sources and used without further purification. Glassy carbon electrode (model XR-335), Ag/AgCl reference electrode (model XR-312) and platinum sheet electrode (model XR-336) were purchased from Shanghai Xianren Instrument Co., Ltd.

Model reaction
The model compound M was synthesized according to a previously reported method40. To a 10 mL oven-dried glass tube fitted with a magnetic stir bar was added cyclopentylboronic acid (2 equiv, 0.4 mmol, 45.6 mg), 4-tert-butylstyrene (1.5 equiv, 0.3 mmol, 55.0 µL), aniline (1 equiv, 0.2 mmol, 18.5 µL), benzaldehyde (1 equiv, 0.2 mmol, 20.4 µL) and 4CzIPN (5 mol%, 7.9 mg). Subsequently, dried 1,4-dioxane (2 mL) was added. The vial was closed with a silica septum and degassed with argon (3 cycles). Afterwards, the vials were irradiated with blue light (λ = 440 nm) at room temperature for 12 h. After the reaction was completed, it was quenched with a saturated ammonium chloride (NH₄Cl) solution and extracted with ethyl acetate (EtOAc). Subsequently, the combined organic layer was dried over anhydrous sodium sulfate (Na₂SO₄), filtered, and concentrated under reduced pressure. Finally, purification by column chromatography afforded the model compound M in 87% yield as a white solid.

Synthesis of Cp-tBu-N3-COF
To a 10 ml glass tube were sequentially added the stirrer, 2,4,6-tris(4-formylphenyl)−1,3,5-triazine (TFTP, 0.06 mmol, 23.6 mg), 80% hydrazine hydrate (HZ, 0.09 mmol, 5.5 µL), 4-tert-butylstyrene (tBs, 0.27 mmol, 49.45 µL), cyclopentylboronic acid (CpBa, 0.36 mmol, 41.0 mg), 4CzIPN (15 mol%, 7.1 mg), 6 M aqueous acetic acid (200 µL), 1,4-dioxane (1.5 mL), n-BuOH (0.5 mL) and N,N-dimethylacetamide (DMA, 0.3 mL). Sonication was carried out for 5 min during which the mixture was dispersed homogeneously and then covered with a rubber stopper to make it a closed system, followed by replacement of the gaseous atmosphere in the system with nitrogen for a duration of 15 min. The reaction tube was subjected to blue LED lamp (λ = 440 nm) irradiation and stirred at room temperature for 72 h. After the reaction was completed, the mixture in the reaction tube was washed sequentially with tetrahydrofuran and dichloromethane and filtered to obtain the corresponding COF materials, after which the Soxhlet extractor was washed in a solvent environment of tetrahydrofuran, acetone, and dichloromethane, respectively, for 12 h. Finally, the materials were dried in a vacuum oven at 100 °C for 8 h to obtain yellow Cp-tBu-N3-COF powder (46.5 mg, 72% yield).

Synthesis of Cy-tBu-N3-COF
To a 10 ml glass tube were sequentially added the stirrer, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (TFTP, 0.06 mmol, 23.6 mg), 80% hydrazine hydrate (HZ, 0.09 mmol, 5.5 µL), 4-tert-butylstyrene (tBs, 0.27 mmol, 49.45 µL), cyclohexylboronic acid (ChBa, 0.36 mmol, 46.0 mg), 4CzIPN (15 mol%, 7.1 mg), 6 M aqueous acetic acid (200 µL), 1,4-dioxane (1.5 mL), n-BuOH (0.5 mL) and N,N-dimethylacetamide (DMA, 0.3 mL). Sonication was carried out for 5 min during which the mixture was dispersed homogeneously and then covered with a rubber stopper to make it a closed system, followed by replacement of the gaseous atmosphere in the system with nitrogen for a duration of 15 min. The reaction tube was subjected to blue LED lamp (λ = 440 nm) irradiation and stirred at room temperature for 72 h. After the reaction was completed, the mixture in the reaction tube was washed sequentially with tetrahydrofuran and dichloromethane and filtered to obtain the corresponding COF materials, after which the Soxhlet extractor was washed in a solvent environment of tetrahydrofuran, acetone, and dichloromethane, respectively, for 12 h. Finally, the materials were dried in a vacuum oven at 100 °C for 8 h to obtain yellow Cy-tBu-N3-COF powder (47.3 mg, 70% yield).

Synthesis of Cy-OMe-N3-COF
To a 10 ml glass tube were sequentially added the stirrer, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (TFTP, 0.06 mmol, 23.6 mg), 80% hydrazine hydrate (HZ, 0.09 mmol, 5.5 µL), 4-methoxystyrene (Meos, 0.27 mmol, 36.5 µL), cyclohexylboronic acid (ChBa, 0.36 mmol, 46.0 mg), 4CzIPN (15 mol%, 7.1 mg), 6 M aqueous acetic acid (200 µL), 1,4-dioxane (1.5 mL), n-BuOH (0.5 mL) and N,N-dimethylacetamide (DMA, 0.3 mL). Sonication was carried out for 5 min during which the mixture was dispersed homogeneously and then covered with a rubber stopper to make it a closed system, followed by replacement of the gaseous atmosphere in the system with nitrogen for a duration of 15 min. The reaction tube was subjected to blue LED lamp (λ = 440 nm) irradiation and stirred at room temperature for 72 h. After the reaction was completed, the mixture in the reaction tube was washed sequentially with tetrahydrofuran and dichloromethane and filtered to obtain the corresponding COF materials, after which the Soxhlet extractor was washed in a solvent environment of tetrahydrofuran, acetone, and dichloromethane, respectively, for 12 h. Finally, the materials were dried in a vacuum oven at 100 °C for 8 h to obtain yellow Cy-OMe-N3-COF powder (42.8 mg, 69% yield).

Synthesis of Cp-F-N3-COF
To a 10 ml glass tube were sequentially added the stirrer, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (TFTP, 0.06 mmol, 23.6 mg), 80% hydrazine hydrate (HZ, 0.09 mmol, 5.5 µL), 4-fluorostyrene (PFS, 0.27 mmol, 32.2 µL), cyclopentylboronic acid (CpBa, 0.36 mmol, 41.0 mg), 4CzIPN (15 mol%, 7.1 mg), 6 M aqueous acetic acid (200 µL), 1,4-dioxane (1.5 mL), n-BuOH (0.5 mL) and N,N-dimethylacetamide (DMA, 0.3 mL). Sonication was carried out for 5 min during which the mixture was dispersed homogeneously and then covered with a rubber stopper to make it a closed system, followed by replacement of the gaseous atmosphere in the system with nitrogen for a duration of 15 min. The reaction tube was subjected to blue LED lamp (λ = 440 nm) irradiation and stirred at room temperature for 72 h. After the reaction was completed, the mixture in the reaction tube was washed sequentially with tetrahydrofuran and dichloromethane and filtered to obtain the corresponding COF materials, after which the Soxhlet extractor was washed in a solvent environment of tetrahydrofuran, acetone, and dichloromethane, respectively, for 12 h. Finally, the materials were dried in a vacuum oven at 100 °C for 8 h to obtain yellow Cp-F-N3-COF powder (38.7 mg, 67% yield).

Photocatalytic synthesis of 2-phenylbenzimidazole
A 10 mL glass tube, fitted with a stir bar, was loaded with o-phenylenediamine (1a, 0.2 mmol), benzaldehyde (2a, 0.2 mmol), Cp-tBu-N3-COF (6 mg), and EtOH (2.0 mL). The reaction mixture was irradiated under 5 W blue LEDs (λ = 440 nm, 200 mW cm−2) for 8 h at room temperature under an air atmosphere. Upon completion of the reaction, the solid product was recovered by filtration, and the filtrate was concentrated under reduced pressure. The resulting residue was subjected to purification via chromatography on silica gel using a petroleum ether/ethyl acetate mixture as the eluent, leading to the isolation of 2-phenylbenzimidazole (3a).

AQY and TOF measurements
The apparent quantum yield (AQY) was calculated according to the formula47:
AQY(%) = (Number of reacted electrons / Number of incident photons) × 100% = (n(product) × NA × h × c / I × S × t × λ) × 100% (1)
where n(product) is the mole number of product (1.94 × 10−4 mol), NA is Avogadro’s number (6.02 × 1023 mol−1), h is Planck’s constant (6.626 × 10−34 J·s), c is the speed of light (3 × 108 ms−1), I is the light intensity (200 mW cm−2), S is the area of irradiation (2.0 cm2), t is irradiation time (8 h), and λ is the light wavelength (440 nm).

The turnover frequency (TOF) was calculated according to the formula48:
TOF = n(product) / (n(catalyst) × t) (2)
where n(product) is the mole number of product (0.194 mmol), n(catalyst) is the mole number of catalyst (0.0055 mmol), t is reaction time (8 h).

Mott-Schottky and electrochemical impedance spectroscopy (EIS) measurements
Mott-Schottky and EIS measurements were carried out on a CHI 660E electrochemical workstation equipped with a three-electrode system, composed of a modified glassy carbon working electrode, a Pt wire counter electrode, and an Ag/AgCl reference electrode46. The working electrode was modified by drop-casting a suspension containing 0.2 mg of COF and 0.7 mg of carbon black in 50 µL of 5% Nafion solution. Mott-Schottky test was recorded in 0.5 M Na₂SO₄ solution (pH = 7.62 ± 0.03) at alternating current frequencies of 2000 Hz, 2500 Hz, and 3000 Hz. EIS measurements were conducted in a 0.1 M KCl electrolyte containing 5 mM K4[Fe(CN)₆]/K3[Fe(CN)₆]. All potentials were not iR corrected and were adjusted to the RHE reference scale using the formula:
ERHE = EAg/AgCl + 0.0591pH + 0.197 (3)
where EAg/AgCl is −0.61 V.

Photocurrent measurements
Photocurrent measurements were conducted on a CHI 660E electrochemical workstation using a standard three-electrode system. The working electrode was prepared by mixing 4 mg of COF, 1 mL of isopropanol/water mixture (1:3, v/v) and 30 μL of Nafion solution, followed by casting 200 μL of the slurry onto FTO glass. The Pt plate and Ag/AgCl served as the counter electrode and the reference electrode, respectively. A 300 W Xenon lamp equipped with a cut-off filter served as the light source, and 0.1 M of Na₂SO₄ solution was used as the electrolyte.

Electron-spin resonance (ESR) measurements
ESR measurements were conducted at the frequency of 9.550 GHz, with a magnetic field scanning range of 3400–3600 G. A powder sample of COF was added to nuclear magnetic tubes. The sealed tube was then irradiated with a 5 W blue LEDs (λ = 440 nm, 200 mW cm−2) for 1 min, followed by the same ESR studies. Spin trapping studies for O2•− detection: 2 mg of COF, 0.1 mmol of aldehyde and amine were dispersed in 95 μL of ethanol, followed by the addition of 5 μL of DMPO and irradiated for 1 min.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This study reports the synthesis of a novel covalent organic framework (COF) via a photocatalytic four-component reaction\n(4CR) and its application in the visible-light-driven synthesis of benzimidazoles. By integrating photocatalysis with\nmulticomponent reaction strategies, this work introduces an innovative and mild approach for COF synthesis. However, the\nlogical structure of the manuscript is not well emphasized, and the characterization methods require further depth and\nrefinement. Therefore, a major revision is recommended.\n1. The photocatalytic four-component synthesis of COFs is the core innovation of this study. However, the manuscript\nprimarily focuses on the application of COFs as photocatalysts, while providing only a brief discussion of the 4CR process. It\nis recommended to adjust the logical focus of the article to better highlight the novelty of the study.\n2. The introduction lacks a comprehensive comparison of existing three-component reactions (3CR), four-component\nreactions (4CR), and other COF synthesis methods. A more detailed discussion is suggested to clarify the advancements of\nthis work.\n3. It is recommended to supplement the screening conditions for the photocatalytic four-component reaction, including\nparameters such as catalyst type, solvent, light source, gas atmosphere, and reaction time.\n4. PXRD data indicate that the COF exhibits high crystallinity. However, the c value of the unit cell is abnormally high. It is\nsuggested to include a schematic representation of the interlayer stacking mode of the COF structure.\n5. HRTEM analysis should be added to measure the corresponding lattice spacing, and the results should be compared with\nPXRD data for consistency verification.\n6. In Figure S2, the assignments of the solid-state NMR peaks should be clearly labeled. Additionally, the peak around 160\nppm in Figure 2b needs further clarification.\n7. A more in-depth evaluation of photocatalytic activity is required, including key parameters such as quantum yield (QY) and\nturnover frequency (TOF).\n8. The manuscript lacks a comparative analysis of catalytic performance with previously reported photocatalytic COFs. It is\nrecommended to supplement relevant data or literature discussion to more intuitively demonstrate the advantages of this\ncatalyst.", "reviewer_2": "Multicomponent reactions (MCRs) are well-established as efficient and environmentally benign synthetic procedures, known\nfor their step economy and operational simplicity. Photo- or electrochemical strategies further enhance these benefits by\nrequiring less energy and operating at room temperature. In this work, the authors have employed a previously known MCR\nmethod to develop a four-component reaction for the synthesis of covalent organic frameworks (COFs). A total of 24\nfunctionalized COFs were synthesized with high crystallinity and permanent porosity using a photocatalytic MCR and\ncharacterized adequately. Additionally, the authors demonstrated the synthetic utility of the produced COFs as\nphotocatalysts for visible-light-driven benzimidazole synthesis. While the methodology is interesting and showcases\npractical applications, I do not find any substantial novelty in the synthetic approach or its photocatalytic application.\nTherefore, I cannot support the acceptance of this manuscript in Nature Communications. However, I have a few comments:\na) The model reaction is basically a repetition of a previously reported procedure. The authors should instead validate their\napproach using hydrazine as an amine equivalent in a four-component reaction system.\nb) The authors initially used tri-2,4,6-tris(4-formylphenyl)-1,3,5-triazine (TFTP) as an aldehyde equivalent, but later, methyl\nfunctionality appears at the para-positions. Could the authors clarify this discrepancy?", "reviewer_3": "This work reports the first rational synthesis of a class of functionalized COFs featuring high crystallinity and permanent\nporosity, achieved via a photocatalytic four-component reaction. I recommend a revision and the specific reasons are as\nfollows:\n1. The authors compared the FT-IR and XPS spectra between Cp-tBu-N3-COF and N3-COF. However, this comparison\nalone is insufficient to quantify the extent of the modification. Moreover, the SSNMR data of N3-COF were not included in the\nanalysis, raising doubts about whether the COF was fully post-modified.\n2. The model compounds lack crystal structure data and should be provided.\n3. The authors stated in the article that the as-obtained COFs are stable up to 200 °C. However, the TGA data show that the\nCOFs start to lose weight at around 150 °C, which differs significantly from the reported weight loss temperatures of other\nCOFs (300 °C). The authors should explain this discrepancy.\n4. The as-obtained COFs exhibit a larger BET than the fully post-modified COFs, along with a heterogeneous pore size\ndistribution containing 2 nm pores. The authors should explain these observations and calculate the theoretical specific\nsurface area of the simulated COF (containing hydrogen atoms), as well as the specific surface area and pore size\ndistribution of the N3-COF.\n5. The authors should compare the obtained COFs with conventional catalytic materials in the catalyzed reactions and\nclarify their advantages in terms of yield, recyclability, and other relevant factors. In addition, the mechanism section should\nincorporate an appropriate explanation, such as calculations."}, "author_response": "The point-to-point response to the comments from the reviewers of NCOMMS-25-\n10690\nReviewer 1’s comments:\nThis study reports the synthesis of a novel covalent organic framework (COF) via a\nphotocatalytic four-component reaction (4CR) and its application in the visible-light-driven\nsynthesis of benzimidazoles. By integrating photocatalysis with\nmulticomponent reaction strategies, this work introduces an innovative and mild approach for COF synthesis.\nHowever, the logical structure of the manuscript is not well emphasized, and the\ncharacterization methods require further depth and refinement. Therefore, a major revision\nis recommended.\nResponse: We appreciate such positive comments very much. Following the reviewer’s\nsuggestion, we have carefully revised our manuscript according to the comments. Please\nsee the details below.\n1. The photocatalytic four-component synthesis of COFs is the core innovation of this study.\nHowever, the manuscript primarily focuses on the application of COFs as photocatalysts,\nwhile providing only a brief discussion of the 4CR process. It is recommended to adjust the\nlogical focus of the article to better highlight the novelty of the study.\nResponse: Thank you very much for your valuable suggestion. As suggested by the\nreviewer, we have adjusted the logical focus of the article to better highlight the novelty of\nthe study throughout the entire manuscript. They have been added in the revised\nmanuscript (please see pages 2-4).\nVisible-light photoredox catalysis has emerged as a powerful approach in synthetic\nchemistry for the synthesis of complex molecules from simple starting materials because\nof its mildness, low-energy consumption, and environmental friendliness. Its versatility has\nalso been demonstrated in providing alternative routes for the construction of COFs.\nCompared with the conventional methods for COFs synthesis, photoredox catalysis\nenables the formation of COFs under mild reaction conditions, while only few examples\nhave been reported thus far. Research on the photocatalytic synthesis of COFs is still in\nthe early stage, and its superior potential remains largely unexploited. Therefore, it is highly\ndesirable yet challenging to explore more novel photocatalytic reactions to provide more\npossibilities in the design and preparation of COFs.\nMulticomponent reactions (MCRs), which involve the one-pot combination of at least three\nsubstrates to form multiple new bonds without separating intermediates, are recognized as\npowerful tools in synthetic chemistry. These reactions are valued for their convenient\noperation, high efficiency, and structural diversity. Recently, different types of MCRs,\nparticularly three-component reactions such as Debus−Radziszewski reaction, Strecker\nreaction, Povarov reaction, and thiazole formation reaction, have been successfully applied\nto construct various COFs. Despite these advances, the extension to four-component\nreactions (4CRs) for COFs synthesis remains largely unexplored, primarily due to the\nsignificantly increased complexity in controlling regio- and chemoselectivity. To date, Wang\nand co-workers reported the only case of the synthesis of functionalized COFs via the\n4CRs using solvothermal method, which represents a major breakthrough in this field. This\nachievement highlights the unique potential of 4CRs to assemble four distinct monomers\nin a one-pot process, enabling the construction of structurally diverse COFs. When\ncomparing various synthetic strategies, although the conventional two-component method\nis operationally simple and straightforward, it has fundamental limitations in terms of\nstructural complexity and functional integration. The three-component reaction can offer\nimproved structural diversity, yet remains constrained by relatively limited combinations of\nbuilding blocks. In contrast, 4CRs offer a greater variety of combinatorial possibilities and\nallow precise integration of multiple functional groups within a single framework. The\ndevelopment of novel 4CRs systems will not only broaden the structural diversity of COFs,\nbut also promote the advancement of their applications.\nGiven the immense potential of both 4CRs and photocatalysis, we propose integrating\nthese two strategies to synthesize functionalized COFs via a photocatalytic four-\ncomponent reaction—a novel approach that has yet to be explored. The innovative merger\nof 4CRs with visible-light photoredox catalysis to synthesize functionalized COFs\nrepresents a groundbreaking advancement in the field of porous material synthesis. Firstly,\nit fully exploited the significant potential of the four-component reactions in achieving\nstructural diversity and functional integration. Secondly, the implementation of\nphotocatalytic technology effectively overcomes the limitations imposed by the\nconventional harsh reaction conditions. Finally, this photocatalytic four-component reaction\nstrategy will open up new avenues for constructing COFs that are otherwise inaccessible\nthrough conventional methods.\nHerein, we successfully applied the photocatalytic four-component reaction strategy for the\nfirst time to synthesize COFs. Using visible-light irradiation and 4CzIPN as the\nphotocatalyst, we effectively constructed a series of novel COFs with high crystallinity and\npermanent porosity via the four-component reaction involving aromatic aldehydes,\nhydrazines, aromatic olefins, and boronic acids. Compared with traditional synthetic\nmethods, this clean-energy-triggered approach herein allowed the precise synthesis of\nstructurally diverse COFs under mild conditions. Furthermore, the obtained Cp-tBu-N -3\nCOF demonstrated excellent photocatalytic performance for the visible-light-driven\nsynthesis of benzimidazoles.\n2. The introduction lacks a comprehensive comparison of existing three-component\nreactions (3CR), four-component reactions (4CR), and other COF synthesis methods. A\nmore detailed discussion is suggested to clarify the advancements of this work.\nResponse: Thank you very much for your valuable suggestion. As suggested by the\nreviewer, we have compared the four-component reactions (4CRs) with the existing three-\ncomponent reactions and conventional two-component reactions comprehensively.\nFurthermore, a more detailed discussion was given to clarify the advancements of this\nwork in the revised manuscript. They have been added in the revised manuscript (please\nsee lines 13-20 on page 3, and the last paragraph on page 13).\nWhen comparing various synthetic strategies, although the conventional two-component\nmethod is operationally simple and straightforward, it has fundamental limitations in terms\nof structural complexity and functional integration. The three-component reaction can offer\nimproved structural diversity, yet remains constrained by relatively limited combinations of\nbuilding blocks. In contrast, 4CRs offer a greater variety of combinatorial possibilities and\nallow precise integration of multiple functional groups within a single framework. The\ndevelopment of novel 4CRs systems will not only broaden the structural diversity of COFs,\nbut also promote the advancement of their applications.\nwe have developed an efficient approach for synthesizing a series of novel COFs using a\nphotocatalytic four-component reaction at room temperature. In addition, the obtained Cp-\ntBu-N -COF exhibited excellent photocatalytic activity in the visible-light-driven\n3\ncondensation-cyclization reaction, affording benzimidazoles in excellent yields. This novel\nphotocatalytic four-component reaction strategy not only addresses the long-standing\nchallenge of harsh reaction conditions in conventional COFs synthesis methods, but also\nenables the integration of four different types of monomers in a one-pot process to create\nstructurally diverse COFs. We believe that this pioneering strategy will bring a significant\nbreakthrough in the methodology development of COFs.\n3. It is recommended to supplement the screening conditions for the photocatalytic four-\ncomponent reaction, including parameters such as catalyst type, solvent, light source, gas\natmosphere, and reaction time.\nResponse: Thank you very much for your valuable suggestion. The synthetic conditions\nwere systematically optimized again by screening key parameters, including the acid,\nsolvent, photocatalyst, light source, gas atmosphere, and reaction time. The selected\nconditions were summarized in Supplementary Figs. 3-6. The optimized conditions were\ndetermined as crystallization in 1,4-dioxane/n-BuOH/DMA mixture (1.5:0.5:0.3, v/v/v) with\nacetic acid as the catalyst and 4CzIPN as the photocatalyst, under visible-light irradiation\nat room temperature for 72 h. Under the optimized conditions, we have re-synthesized and\nre-characterized the three COFs. They have been added in the revised manuscript (please\nsee the last paragraph on page 4) and Supplementary Figs. 3-6 of the revised\nSupplementary Information (please see pages S7-8).\nSupplementary Fig. 3 (a) PXRD patterns and (b) FT-IR spectra of Cp-tBu-N -COF\n3\nsynthesized with different acid concentrations. The results indicate that adding 200 µL of 6\nM HOAc gives the best result.\nSupplementary Fig. 4 (a) PXRD patterns and (b) FT-IR spectra of Cp-tBu-N -COF\n3\nsynthesized with different solvents.\nSupplementary Fig. 5 (a) PXRD patterns and (b) FT-IR spectra of Cp-tBu-N -COF\n3\nsynthesized with different solvents. The results indicate that 1,4-dioxane/n-BuOH/DMA\nmixture (1.5:0.5:0.3, v/v/v) was the optimized conditions.\nSupplementary Fig. 6 (a) PXRD patterns and (b) FT-IR spectra of Cp-tBu-N -COF\n3\nsynthesized with different photocatalyst, light source, gas atmosphere, and reaction time.\nThe results proved to be inferior to the optimized conditions.\n4. PXRD data indicate that the COF exhibits high crystallinity. However, the c value of the\nunit cell is abnormally high. It is suggested to include a schematic representation of the\ninterlayer stacking mode of the COF structure.\nResponse: Thank you very much for your valuable suggestion. The schematic\nrepresentation of the interlayer stacking mode of the three COFs was shown as below.\nBased on crystal structure analysis, the eclipsed 2D structure of Cp-tBu-N -COF contains\n3\nhexagonal pores (d = ca. 1.4 nm) with an interlayer distance determined as ca. 6.10 Å. The\nrelatively high c-value is probably caused by the incorporation of sterically bulky tert-butyl\nand cyclopentyl moieties within the COFs structure. They have been added in the revised\nmanuscript (please see Fig. 2d and lines 12-13 on page 6) and Supplementary Figs. 18b\nand 27b of the revised Supplementary Information (please see page S21 and page S28).\nFig. R1 The side views of the eclipsed structures proposed for (a) Cp-tBu-N -COF, (b) Cy-\n3\ntBu-N -COF, and (c) Cy-OMe-N -COF.\n3 3\n5. HRTEM analysis should be added to measure the corresponding lattice spacing, and\nthe results should be compared with PXRD data for consistency verification.\nResponse: Thank you very much for your valuable suggestion. The high-resolution\ntransmission electron microscopy (HRTEM) images of the three COFs were measured as\nshown below. The HRTEM image of Cp-tBu-N -COF clearly showed the ordered crystalline\n3\nlattice fringes with an interplanar distance of 0.61 nm, which agreed well with the vertical\ninterlayer spacing of the simulated models. These results confirmed the highly crystalline\nand ordered porous structure of Cp-tBu-N -COF. They have been added in the revised\n3\nmanuscript (please see lines 5-9 on page 7) and Supplementary Figs. 10, 20 and 29 of the\nrevised Supplementary Information (please see pages S9, S22, and S29).\nFig. R2 High-resolution transmission electron microscopy (HRTEM) images and selected\narea electron diffraction (SAED) analysis of (a) Cp-tBu-N -COF, (b) Cy-tBu-N -COF, and\n3 3\n(c) Cy-OMe-N -COF.\n3\n6. In Figure S2, the assignments of the solid-state NMR peaks should be clearly labeled.\nAdditionally, the peak around 160 ppm in Figure 2b needs further clarification.\nResponse: Thank you very much for your valuable suggestion. We have re-performed the\nmodel reaction using benzaldehyde instead of 4-fluorobenzaldehyde, which afforded the\nnew model compound M in 87% yield as shown below. In the 13C NMR spectrum of the\nmodel compound M, the assignments of the NMR peaks have been clearly labeled as\nshown in Supplementary Fig. 2. The peaks at 63, 31 and 25 ppm were assigned to the\ncarbons in C-NH, tert-butyl, and cyclopentyl moieties, respectively. They have been added\nin the revised manuscript (please see lines 12-14 on page 4) and Supplementary Fig. 2 of\nthe revised Supplementary Information (please see page S5).\nFig. R3 The model reaction.\nSupplementary Fig. 2 13C NMR spectrum of the model compound M.\nIn the solid-state NMR spectrum of previously obtained Cp-tBu-N -COF, the peak around\n3\n160 ppm in Figure 2b might be attributed to the imine linkage from incomplete modification.\nIn order to further enhance the degree of the modification via this strategy, we have\nsystematically optimized the synthetic conditions again by screening key parameters,\nincluding the acid, solvent, photocatalyst, light source, gas atmosphere, and reaction time,\nas summarized in Supplementary Figs. 3-6. After extensive optimization of the reaction\nconditions, the degree of modification in the COFs was significantly enhanced. Under the\noptimized conditions, we have re-synthesized the three COFs and re-measured their 13C\nCP-MAS solid-state NMR spectra as shown below. In the 13C CP-MAS solid-state NMR\nspectra of the three COFs, the signal at 162 ppm corresponding to the imine carbon was\nsignificantly weakened, which provided solid evidence for the successful conversion of the\nimine linkage. In the 13C CP-MAS solid-state NMR spectrum of Cy-OMe-N -COF, the signal\n3\nat 159 ppm was attributed to the carbon atom of the benzene ring connected to the\nmethoxy group. They have been added in the revised manuscript (please see the last four\nlines on page 5 and Fig. 2b on page 6) and Supplementary Figs. 8, 16 and 25 of the revised\nSupplementary Information (please see pages S8, S20, and S28).\nFig. R4 (a) 13C CP/MAS solid-state NMR spectrum of Cp-tBu-N -COF. (b) Comparison of\n3\nthe 13C CP/MAS solid-state NMR spectra of Cp-tBu-N -COF and N -COF. (c) Comparison\n3 3\nof the 13C CP/MAS solid-state NMR spectra of Cy-tBu-N -COF and N -COF. (d)\n3 3\nComparison of the 13C CP/MAS solid-state NMR spectra of Cy-OMe-N -COF and N -COF.\n3 3\n7. A more in-depth evaluation of photocatalytic activity is required, including key\nparameters such as quantum yield (QY) and turnover frequency (TOF).\nResponse: Thank you very much for your valuable suggestion. To further evaluate the\nphotocatalytic activity of Cp-tBu-N -COF in the benzimidazole formation reaction, the\n3\napparent quantum yield (AQY) and turnover frequency (TOF) were calculated to be 0.46%\nand 4.39 h-1, respectively. They have been added in the revised manuscript (please see\nlines 12-13 on page 10) and the revised Supplementary Information (please see page S13).\nThe apparent quantum yield (AQY) was calculated according to the formula (J. Am. Chem.\nSoc. 2025, DOI: 10.1021/jacs.5c07315): AQY (100%) = (Number of reacted\nelectrons)/(Number of incident photons)*100% = (n *N *h*c)/(I*S*t*λ)*100%, where\n(product) A\nn is the mole number of product, N is Avogadro’s number (6.02×1023 mol-1), h is\n(product) A\nPlanck’s constant (6.626×10-34 J·s), c is the speed of light (3×108 m s-1), I is the light\nintensity (200 mW cm-2), S is the area of irradiation (2.0 cm2), t is irradiation time, and λ is\nthe light wavelength (440 nm).\nThe turnover frequency (TOF) was calculated according to the formula (Angew. Chem. Int.\nEd. 2025, DOI: 10.1002/anie.202518707): TOF = (mol product generated)/(mol catalyst h).\n8. The manuscript lacks a comparative analysis of catalytic performance with previously\nreported photocatalytic COFs. It is recommended to supplement relevant data or literature\ndiscussion to more intuitively demonstrate the advantages of this catalyst.\nResponse: Thank you very much for your valuable suggestion. A brief summary and\ncomparison of different heterogeneous catalysts for the photocatalytic condensation–\ncyclization reaction between o-phenylenediamine and benzaldehyde is provided as shown\nbelow. The photocatalytic activity of Cp-tBu-N -COF rivalled that of most reported\n3\nheterogeneous photocatalysts for this reaction. They have been added in the revised\nmanuscript (please see lines 10-11 on page 10) and Supplementary Table 2 of the revised\nSupplementary Information (please see pages S12-S13).\nSupplementary Table 2. Summary and comparison of different heterogeneous catalysts for the\nphotocatalytic condensation–cyclization reaction between o-phenylenediamine and benzaldehyde\nAtmos Light Time Yield Recyclability\nPhotocatalyst Solvent Ref.\nphere Source (h) (%) (cycles)\nThis\nCp-tBu-N3-COF air blue LEDs EtOH 8 97\n5 work\nQL-TzDva air blue LEDs EtOH 6 93 5 2\nBTT-CMP air blue LEDs MeOH 3 93 15 3\nCu/Cu2O@g- 5\nair LEDs H2O 4 83 4\nC3N4\ntungsten 5\nC-BTH air CH3CN 3.5 89 5\nlamp\nNQ-COFD4-Me O2 blue LEDs EtOH/H2O 12 97 5 6\nNQ-COFA1- 5\nO2 blue LEDs EtOH/H2O 24 99 7\nOPR\nBDFe-COF O2 blue LEDs MeOH 2 94 6 8\nBTT-TPA-COF O2 blue LEDs EtOH 7 85 8 9\nBO-COFF3 O2 blue LEDs EtOH/H2O 24 95 5 10\nTPT-COF air blue LEDs EtOH 6 80 5 11\nTZ-HCP1D air white LEDs EtOH 1 99 21 12\nfluorescent 12\nRu-POP air EtOH 2 99 13\nbulb\nCuO@Ag/NH2- 5\nair LEDs EtOH 3 95 14\nMIL-88B\nPAF-366 air blue LEDs EtOH 3 99 10 15\nPAF-380 air blue LEDs EtOH 3 99 10 16\nTTA-CMP air blue LEDs EtOH 2 98 12 17\nCbzCMP-12 O2 blue LEDs MeOH 2 99 / 18\nBTT-CMP2 O2 blue LEDs EtOH 2 91 10 19\nReviewer 2’s comments:\nMulticomponent reactions (MCRs) are well-established as efficient and environmentally\nbenign synthetic procedures, known for their step economy and operational simplicity.\nPhoto- or electrochemical strategies further enhance these benefits by requiring less\nenergy and operating at room temperature. In this work, the authors have employed a\npreviously known MCR method to develop a four-component reaction for the synthesis of\ncovalent organic frameworks (COFs). A total of 24 functionalized COFs were synthesized\nwith high crystallinity and permanent porosity using a photocatalytic MCR and\ncharacterized adequately. Additionally, the authors demonstrated the synthetic utility of the\nproduced COFs as photocatalysts for visible-light-driven benzimidazole synthesis. While\nthe methodology is interesting and showcases practical applications, I do not find any\nsubstantial novelty in the synthetic approach or its photocatalytic application. Therefore, I\ncannot support the acceptance of this manuscript in Nature Communications. However, I\nhave a few comments:\nResponse: Thank you very much for your valuable suggestion. We have highlighted the\nnovelty and advantages of the photocatalytic four-component reaction methodology for\nconstructing COFs in the revised manuscript. This innovative approach represents an area\nthat remains unexplored in the field. They have been added in the revised manuscript\n(please see the introduction section on pages 2-4, and discussion section on pages 13-\n14).\nMulticomponent reactions (MCRs) are recognized as powerful tools in synthetic chemistry\ndue to their convenient operation, high efficiency, and structural diversity. MCRs based on\nthree-component reactions have been successfully applied to construct various COFs.\nDespite these advances, the extension to four-component reactions (4CRs) for COFs\nsynthesis remains largely unexplored, primarily due to the significantly increased\ncomplexity in controlling regio- and chemoselectivity. To date, Wang and co-workers\nreported the only case of the synthesis of functionalized COFs via the four-component\nreactions (4CRs) using solvothermal method, which represents a significant breakthrough\nin this field. Compared with the three-component reactions, 4CRs offer a greater variety of\ncombinatorial possibilities and allow precise integration of multiple functional groups within\na single framework. On the other hand, visible-light photoredox catalysis has emerged as\na powerful approach in synthetic chemistry for the synthesis of complex molecules from\nsimple starting materials because of its mildness, low-energy consumption, and\nenvironmental friendliness. Research on the photocatalytic synthesis of COFs is still in the\nearly stage, and its superior potential remains largely unexploited. Therefore, it is highly\ndesirable yet challenging to explore more novel photocatalytic reactions to provide more\npossibilities in the design and preparation of COFs.\nGiven the immense potential of both 4CRs and photocatalysis, we propose integrating\nthese two strategies to synthesize functionalized COFs via a photocatalytic four-\ncomponent reaction—a novel approach that has yet to be explored. The innovative merger\nof 4CRs with visible-light photoredox catalysis to synthesize functionalized COFs\nrepresents a groundbreaking advancement in the field of porous material synthesis. Firstly,\nit fully exploited the significant potential of the four-component reactions in achieving\nstructural diversity and functional integration. Secondly, the implementation of\nphotocatalytic technology effectively overcomes the limitations imposed by the\nconventional harsh reaction conditions. Finally, this photocatalytic four-component reaction\nstrategy will open up new avenues for constructing COFs that are otherwise inaccessible\nthrough conventional methods.\nThis novel photocatalytic four-component reaction strategy not only addresses the long-\nstanding challenge of harsh reaction conditions in conventional COFs synthesis methods,\nbut also enables the integration of four different types of monomers in a one-pot process\nto create structurally diverse COFs. We believe that this pioneering strategy will bring a\nsignificant breakthrough in the methodology development of COFs.\n1. The model reaction is basically a repetition of a previously reported procedure. The\nauthors should instead validate their approach using hydrazine as an amine equivalent in\na four-component reaction system.\nResponse: Thank you very much for your valuable suggestion. According to the reviewer's\nsuggestion, we have performed the model reaction using hydrazine instead of aniline as\nthe amine equivalent. We optimized the reaction conditions extensively and confirmed the\nformation of the desired product through high-resolution mass spectrometry (HRMS) as\nshown below. However, the yield was too low to allow for separation and purification by\ncolumn chromatography. The different reaction efficiencies of the photocatalytic four-\ncomponent reaction in the synthesis of model compound and COFs might be attributed to\nthe different reduction potentials of imine bonds in small molecules and conjugated\npolymers.\nFig. R5 HRMS spectrum of the target product. HRMS (ESI) m/z [M+H]+ calcd for C H N\n48 64 2\n669.5148, Found: 669.5142.\nThe proposed mechanism for this photocatalytic four-component reaction involves a key\nstep: the imine will be reduced by the photosensitizer via a single-electron transfer process,\ngenerating a carbon-centered radical (Org. Lett. 2023, 25, 4010-4015). This radical then\nparticipates in radical coupling reaction to form the final product. Compared with small\nmolecules, the extended conjugated structure in COFs enables the delocalization of\nelectrons and lowers the energy level of the lowest unoccupied molecular orbital (LUMO),\nthereby facilitating the reduction process (Nat. Commun. 2018, 9, 4143). Therefore,\nalthough this photocatalytic four-component reaction can effectively synthesize COFs, its\nefficiency is much lower when synthesizing the corresponding small molecules.\nFig. R6 proposed mechanism for this photocatalytic four-component reaction.\nTherefore, we chose aniline, which has a similar structure but is more conducive to the\nphotocatalytic reaction, as the amine equivalent. We also replaced the original 4-\nfluorobenzaldehyde with benzaldehyde, and then re-performed the model reaction. The\nnew model compound M was characterized by FT-IR, 1H NMR, 13C NMR, and HRMS as\nshown below. They have been added in the revised manuscript (please see lines 12-14 on\npage 4) and Supplementary Figs. 1-2 of the revised Supplementary Information (please\nsee pages S4-S5).\nFig. R3 The model reaction.\nSupplementary Fig. 1 FT-IR spectrum of the model compound M.\nSupplementary Fig. 2 1H NMR, 13C NMR, and HRMS spectra of the model compound M.\n2. The authors initially used tri-2,4,6-tris(4-formylphenyl)-1,3,5-triazine (TFTP) as an\naldehyde equivalent, but later, methyl functionality appears at the para-positions. Could\nthe authors clarify this discrepancy?\nResponse: Thank you very much for your valuable suggestion, and we sincerely apologize\nfor making the ambiguity. The single bond attached to the TFTP moiety was intended to\nindicate the structural extension of the COFs. We have now corrected the structures of all\nthe COFs by changing the single bond to a wavy line in the revised manuscript (please see\nFig. 1 on page 5).\nIntens.5\nx10\n6\n4\n2\n0\n404 406 408 410\n412.2987\n412\n413.3022\n414.3054\n414\n20251021-1.d: +M\nm/z\nFig. 1 Synthesis of Cp-tBu-N -COF, Cy-tBu-N -COF, and Cy-OMe-N -COF.\n3 3 3\nReviewer 3’s comments:\nThis work reports the first rational synthesis of a class of functionalized COFs featuring\nhigh crystallinity and permanent porosity, achieved via a photocatalytic four-component\nreaction. I recommend a revision and the specific reasons are as follows:\nResponse: We appreciate such positive comments very much. Following the reviewer’s\nsuggestion, we have carefully revised our manuscript according to the comments. Please\nsee the details below.\n1. The authors compared the FT-IR and XPS spectra between Cp-tBu-N -COF and N -\n3 3\nCOF. However, this comparison alone is insufficient to quantify the extent of the\nmodification. Moreover, the SSNMR data of N -COF were not included in the analysis,\n3\nraising doubts about whether the COF was fully post-modified.\nResponse: Thank you very much for your valuable suggestion. During the revision\nprocess, we found that the previously obtained COFs might exhibit an incomplete\nmodification. In order to further enhance the degree of the modification via this strategy,\nwe have systematically optimized the synthetic conditions again by screening key\nparameters, including the acid, solvent, photocatalyst, light source, gas atmosphere, and\nreaction time, as summarized in Supplementary Figs. 3-6. After extensive optimization of\nthe reaction conditions, the degree of modification in the COFs was significantly enhanced.\nUnder the optimal conditions, we have re-synthesized the three COFs and re-measured\ntheir 13C CP-MAS solid-state NMR spectra as shown below. For comparation, the 13C CP-\nMAS solid-state NMR spectrum of the pristine imine-based N -COF was also synthesized\n3\nand characterized. In the 13C CP-MAS solid-state NMR spectrum of Cp-tBu-N -COF,\n3\nresonance signals at 67, 31 and 25 ppm were observed, assigned to the carbons in C-NH,\ntert-butyl, and cyclopentyl moieties, respectively. Compared with N -COF, the signal at 162\n3\nppm corresponding to the imine carbon was significantly weakened, indicating the nearly\nquantitative transformation of the imine linkage. They have been added in the revised\nmanuscript (please see the last four lines on page 5 and Fig. 2b on page 6) and\nSupplementary Figs. 8, 16 and 25 of the revised Supplementary Information (please see\npages S8, S20, and S28).\nFig. R4 (a) 13C CP/MAS solid-state NMR spectrum of Cp-tBu-N -COF. (b) Comparison of\n3\nthe 13C CP/MAS solid-state NMR spectra of Cp-tBu-N -COF and N -COF. (c) Comparison\n3 3\nof the 13C CP/MAS solid-state NMR spectra of Cy-tBu-N -COF and N -COF. (d)\n3 3\nComparison of the 13C CP/MAS solid-state NMR spectra of Cy-OMe-N -COF and N -COF.\n3 3\nThe signal at 159 ppm was attributed to the carbon atom of the benzene ring connected to\nthe methoxy group.\nWe have also re-measured the FT- IR spectra of the three re-synthesized COFs as shown\nbelow. Compared with the pristine imine-based N -COF, the peak at approximately 1622\n3\ncm-1 corresponding to the C=N stretch was strongly attenuated, while new peaks appeared\nat 2864 and 2908 cm-1, associated with the cyclopentyl species, and at 2955 cm-1,\ncorresponding to the tert-butyl group, indicating the successful conversion of the imine\nlinkages. They have been added in the revised manuscript (please see the last paragraph\non page 5 and Fig. 2a on page 6) and Supplementary Figs. 7, 14, 15, 23 and 24 of the\nrevised Supplementary Information (please see pages S8, S20, and S27).\nFig. R7 Comparison of the FT-IR spectra of Cp-tBu-N\n3\n-COF and N\n3\n-COF.\nFig. R8 Comparison of the FT-IR spectra of Cy-tBu-N\n3\n-COF and N\n3\n-COF. The peaks at\n1704 cm-1 for C=O and 3356 cm-1 for N-H were strongly attenuated, while the characteristic\npeaks at 2851 and 2923 cm-1 associated with the cyclohexyl species, and 2955 cm-1\ncorresponding to the tert-butyl group appeared, indicating the successful formation of Cy-\ntBu-N -COF.\n3\n-COF and N\n3\n-COF. The peaks at\n1704 cm-1 for C=O and 3356 cm-1 for N-H were strongly attenuated, while the characteristic\npeaks at 2850 and 2923 cm-1 associated with the cyclohexyl species, and 1246 cm-1\ncorresponding to the methoxy group appeared, indicating the successful formation of Cy-\nOMe-N -COF.\n3\nincorporating fluorine atom was designed and synthesized using this strategy to allow for\nprecise quantitative analysis. The corresponding elemental mapping images of the SEM\nmeasurement proved the uniform distribution of the C, N and F elements. Furthermore, the\ncontent of F in Cp-F-N -COF was deternined to be 5.07 wt% by EDX analysis. Therefore,\n3\nthe degree of modification was evaluated to be 80% for Cp-F-N -COF. Compared with the\n3\nelectron-deficient 4-fluorostyrene, the electron-rich 4-tert-butylstyrene and 4-\nmethoxystyrene exhibit much higher activity in the photocatalytic four-component reaction\n(Org. Lett. 2023, 25, 4010-4015). Taking into account the characterizations of Cp-tBu-N -\n3 3\nCOFs cannot be precisely quantified, we speculate that they are much higher than that of\nCp-F-N -COF. The synthesis and characterization of Cp-F-N -COF have been added in\n3 3\nthe revised Supplementary Information (please see Supplementary Figs. 32-40 on pages\nS33-S39).\nFig. R10 Synthesis of Cp-F-N -COF.\nformylphenyl)-1,3,5-triazine (TFTP), 4-fluorostyrene (PFS), cyclopentylboronic acid\n(CpBa), and Cp-F-N -COF. The peaks at 1704 cm-1 for C=O and 3356 cm-1 for N-H were\n3\nstrongly attenuated, while the characteristic peaks at 2864 and 2940 cm-1 associated with\nthe cyclopentyl species, and 1224 cm-1 corresponding to the C-F bond appeared, indicating\nthe successful formation of Cp-F-N -COF.\n3 3\nSupplementary Fig. 34 Comparison of the 13C CP/MAS solid-state NMR spectra of Cp-F-\nN -COF and N -COF. The signal at 159 ppm was attributed to the carbon atom of the\n3 3\nbenzene ring connected to the fluorine group.\nSupplementary Fig. 35 (a) XPS survey spectrum of Cp-F-N -COF. (b) F 1s XPS spectrum\n3\nof Cp-F-N -COF. (c) Comparison of N 1s XPS spectra of Cp-F-N -COF (below) and N -\n3 3 3\nCOF (above).\nSupplementary Fig. 36 (a) Indexed experimental (red), Pawley-refined (black), and\nsimulated (green) PXRD patterns of Cp-F-N -COF. The difference plot is presented in blue.\n7.11°, and 9.43°, which were attributed to (100), (110), (200), and (210) planes, respectively.\n(b) The top and side views of the eclipsed structure proposed for Cp-F-N -COF.\n2 3\nThe pore size distribution curve based on nonlocal density functional theory (NLDFT)\nanalysis is shown as inset. The Brunauer-Emmett-Teller (BET) surface area was\ndetermined as 302 m2g-1, and the total pore volumes (P/P = 0.99) was calculated to be\n0\n0.22 cm3g-1. Calculated by nonlocal density functional theory (NLDFT), the pore size\ndistribution for Cp-F-N -COF was mainly centered at ca. 1.44 nm.\n2. The model compounds lack crystal structure data and should be provided.\nResponse: Thank you very much for your valuable suggestion. To obtain the single crystal,\nwe attempted various crystallization methods, including slow solvent evaporation, liquid\ndiffusion, and slow cooling. However, no diffraction-quality single crystals were obtained. It\nis presumably attributed to the presence of flexible alkyl chain in the structure, which\nintroduces conformational disorder, thereby further complicating the crystallization process.\nAlthough single crystals were not obtained, the model compound M was comprehensively\ncharacterized by 1H NMR, 13C NMR, and high-resolution mass spectrum. These data agree\nwell with the previous report (Org. Lett. 2023, 25, 4010-4015), which fully confirm the\nmolecular structure. They have been added in the revised manuscript (please see lines\n12-14 on page 4) and Supplementary Figs. 1-2 of the revised Supplementary Information\n(please see pages S4-S5).\n3. The authors stated in the article that the as-obtained COFs are stable up to 200 °C.\nHowever, the TGA data show that the COFs start to lose weight at around 150 °C, which\ndiffers significantly from the reported weight loss temperatures of other COFs (300 °C).\nThe authors should explain this discrepancy.\nResponse: Thank you very much for your valuable suggestion. The weight loss of the\npreviously obtained COFs starting at 150 °C might be attributed to the evolution of\nincompletely removed guest molecules or residual solvents from the pores upon heating.\nUnder the optimized conditions, we have re-synthesized the three COFs. The three re-\nsynthesized COFs were thoroughly washed, dried, and subsequently characterized by\nthermogravimetric analysis (TGA) as shown below, which revealed that the materials\nremain stable up to 260 C. They have been added in the revised manuscript (please see\nlines 10-11 and Fig. 3b on page 7) and Supplementary Figs. 21 and 30 of the revised\nSupplementary Information (please see page S22 and page S30).\nFig. R11 Thermogravimetric analysis (TGA) curve of (a) Cp-tBu-N -COF, (b) Cy-tBu-N -\n3 3\nCOF and (c) Cy-OMe-N -COF.\n3\n4. The as-obtained COFs exhibit a larger BET than the fully post-modified COFs, along\nwith a heterogeneous pore size distribution containing 2 nm pores. The authors should\nexplain these observations and calculate the theoretical specific surface area of the\nsimulated COF (containing hydrogen atoms), as well as the specific surface area and pore\nsize distribution of the N -COF.\nCOFs exhibit a heterogeneous pore size distribution, including pores of 2 nm, potentially\nattributed to incomplete modification. In order to further enhance the degree of the\nmodification via this strategy, we have systematically optimized the synthetic conditions\nagain by screening key parameters, including the acid, solvent, photocatalyst, light source,\ngas atmosphere, and reaction time, as summarized in Supplementary Figs. 3-6. After\nextensive optimization of the reaction conditions, the degree of modification in the COFs\nwas significantly enhanced. Under the optimized conditions, we have re-synthesized the\nthree COFs and re-measured their BET as shown below. The BET surface areas of the\nthree COFs were determined to be 392, 464, and 441 m2g-1, respectively. Moreover,\nnonlocal density functional theory (NLDFT) analysis revealed that the average pore width\nof the three COFs was determined to be 1.35, 1.34, and 1.40 nm respectively, which agree\nwell with the pore size calculated from the simulated crystal structure. The wide pore size\ndistribution of COFs may result from the presence of flexible alkyl groups (J. Am. Chem.\nSoc. 2024, 146, 4822-4829; Adv. Energy Mater. 2025, 2501193). For comparation, the\npristine imine-based N -COF was also characterized, exhibiting a BET surface area of\n3\n1828 m2g-1 and an average pore width of 2.5 nm. The BET surface areas of the three COFs\nare much lower than that of the imine-based N -COF, which serves as further evidence for\n3\ntheir successful synthesis. They have been added in the revised manuscript (please see\nthe last paragraph on page 6 and Fig. 3a on page 7) and Supplementary Figs. 19 and 28\nof the revised Supplementary Information (please see page S21 and page S29).\nFig. R12 N adsorption and desorption isotherms of (a) Cp-tBu-N -COF, (b) Cy-tBu-N -\n2 3 3\nCOF, (c) Cy-OMe-N -COF and (d) N -COF at 77 K. The pore size distribution curve based\n3 3\non nonlocal density functional theory (NLDFT) analysis is shown as inset.\nFurthermore, the theoretical specific surface areas of the simulated COFs (containing\nhydrogen atoms) were also calculated using Materials Studio (version 2018). The\ntheoretical specific surface areas of the three COFs were determined to be 561, 596 and\n655 m2g-1, respectively. The theoretical specific surface area of the pristine imine-based\nN -COF was determined to be 2052 m2g-1. The experimentally determined BET surface\n3\nareas are all lower than the theoretically calculated values. This discrepancy is reasonable,\nattributable to structural imperfections in the synthesized COFs and the inherent limitations\nof the characterization techniques.\n5. The authors should compare the obtained COFs with conventional catalytic materials in\nthe catalyzed reactions and clarify their advantages in terms of yield, recyclability, and\nother relevant factors. In addition, the mechanism section should incorporate an\nappropriate explanation, such as calculations.\nResponse: Thank you very much for your valuable suggestion. A brief summary and\ncomparison of different heterogeneous catalysts for the photocatalytic condensation–\ncyclization reaction between o-phenylenediamine and benzaldehyde is provided as shown\nbelow. The photocatalytic activity of Cp-tBu-N -COF rivalled that of most reported\n3\nheterogeneous photocatalysts for this reaction. They have been added in the revised\nmanuscript (please see lines 10-11 on page 10) and Supplementary Table 2 of the revised\nSupplementary Information (please see pages S12-S13).\nSupplementary Table 2. Summary and comparison of different heterogeneous catalysts for the\nphotocatalytic condensation–cyclization reaction between o-phenylenediamine and benzaldehyde\nAtmos Light Time Yield Recyclability\nPhotocatalyst Solvent Ref.\nphere Source (h) (%) (cycles)\nThis\nCp-tBu-N3-COF air blue LEDs EtOH 8 97\n5 work\nQL-TzDva air blue LEDs EtOH 6 93 5 2\nBTT-CMP air blue LEDs MeOH 3 93 15 3\nCu/Cu2O@g- 5\nair LEDs H2O 4 83 4\nC3N4\ntungsten 5\nC-BTH air CH3CN 3.5 89 5\nlamp\nNQ-COFD4-Me O2 blue LEDs EtOH/H2O 12 97 5 6\nNQ-COFA1- 5\nO2 blue LEDs EtOH/H2O 24 99 7\nOPR\nBDFe-COF O2 blue LEDs MeOH 2 94 6 8\nBTT-TPA-COF O2 blue LEDs EtOH 7 85 8 9\nBO-COFF3 O2 blue LEDs EtOH/H2O 24 95 5 10\nTPT-COF air blue LEDs EtOH 6 80 5 11\nTZ-HCP1D air white LEDs EtOH 1 99 21 12\nfluorescent 12\nRu-POP air EtOH 2 99 13\nbulb\nCuO@Ag/NH2- 5\nair LEDs EtOH 3 95 14\nMIL-88B\nPAF-366 air blue LEDs EtOH 3 99 10 15\nPAF-380 air blue LEDs EtOH 3 99 10 16\nTTA-CMP air blue LEDs EtOH 2 98 12 17\nCbzCMP-12 O2 blue LEDs MeOH 2 99 / 18\nBTT-CMP2 O2 blue LEDs EtOH 2 91 10 19\nWe have also incorporated some explanations for the reaction mechanism. In order to\nprove the thermodynamic feasibility of the photocatalytic reaction, the energy levels of Cp-\ntBu-N -COF were determined by the solid-state UV-vis diffuse reflectance spectrum and\nthat Cp-tBu-N -COF was a kind of n-type semiconductor (Fig. 4c). The flat band of Cp-tBu-\ndetermined to be 2.39 V vs. NHE (Fig. 4d). Because the CB of Cp-tBu-N -COF is more\n3\nnegative than the reduction potential of O /O •− (−0.33 V vs. NHE), it can\n2 2\nthermodynamically drive photocatalytic organic transformations mediated by O •−. They\n2\nhave been added in the revised manuscript (please see Fig. 4 and lines 4-14 on page 8).\nFig. 4 Photophysical and electrochemical properties of Cp-tBu-N -COF. (a) The UV-\n3\nvis diffuse reflectance spectrum of Cp-tBu-N -COF. (b) The Tauc plots for the determination\n3\nof the optical band gap of Cp-tBu-N -COF. (c) Mott-Schottky plots of Cp-tBu-N -COF. (d)\n3 3\nEnergy band structure of Cp-tBu-N -COF.\nresponse were also investigated. Cp-tBu-N -COF exhibited small Nyquist radius and\n3\nstrong transient photocurrent response, indicating its small charge-transfer resistance and\nhigh photogenerated carriers transport efficiency. All the obtained results demonstrated\nthat Cp-tBu-N -COF could act as a promising photocatalyst. They have been added in the\n3\nrevised manuscript (please see lines 14-18 on page 8) and Supplementary Fig. 11 of the\nrevised Supplementary Information (please see page S9).\nSupplementary Fig. 11 (a) Electrochemical impedance spectroscopy (EIS) Nyquist plot\nof Cp-tBu-N -COF. (b) Photocurrent response of Cp-tBu-N -COF.\n3 3\nDensity functional theory (DFT) computations were applied to visualize the highest\noccupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)\nof the segment of Cp-tBu-N -COF (Supplementary Fig. 13). The HOMO and LUMO of the\n3\nsegment are mainly located at the hydrazine unit and the triazine moiety respectively,\nindicating that there is sufficient intramolecular charge transfer (ICT) within the framework.\nTherefore, Cp-tBu-N -COF can efficiently convert triplet oxygen into superoxide anion\n3\nradicals (O •−) via a single-electron transfer process. They have been added in the revised\n2\nmanuscript (please see lines 25-30 on page 12) and Supplementary Fig. 13 of the revised\nSupplementary Information (please see page S18).\nSupplementary Fig. 13 Molecular-orbital distribution of the HOMO and LUMO for the\nsegment of Cp-tBu-N -COF.\n3"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The author made excellent revisions to the manuscript, providing reasonable responses and explanations for each of the reviewers' comments. I have no other opinions. I support the publication of this manuscript.", "reviewer_2": "The revised manuscript includes comments and revisions from all reviewers, and they have been adequately addressed.\nThe authors have also attempted to justify the novelty of the manuscript by citing the complexity of the synthesis, the challenges involved, and the limited availability of related literature for the synthesis of COFs. I agree that the literature on similar four-component reactions is still scarce. However, I still find limited novelty in terms of the underlying chemistry or the mechanistic rationale presented.\nThat said, I leave the final decision regarding the fate of this manuscript to the Editor.", "reviewer_3": "The authors have answered most of the questions. One question is whether the as-obtained COFs are stable up to 200 °C, TGA data is not enough to make this claim. The authors should test the PXRD at different temperatures."}, "author_response": "The point-to-point response to the comments from the reviewers of NCOMMS-25-\n10690A\nReviewer 1’s comments:\nThe author made excellent revisions to the manuscript, providing reasonable responses\nand explanations for each of the reviewers' comments. I have no other opinions. I support\nthe publication of this manuscript.\nResponse: We sincerely thank the reviewer for taking time to review our manuscript and\nappreciate the positive comments and recommendation of our work.\nReviewer 2’s comments:\nThe revised manuscript includes comments and revisions from all reviewers, and they have\nbeen adequately addressed. The authors have also attempted to justify the novelty of the\nmanuscript by citing the complexity of the synthesis, the challenges involved, and the\nlimited availability of related literature for the synthesis of COFs. I agree that the literature\non similar four-component reactions is still scarce. However, I still find limited novelty in\nterms of the underlying chemistry or the mechanistic rationale presented.\nThat said, I leave the final decision regarding the fate of this manuscript to the Editor.\nResponse: We sincerely thank the reviewer for taking time to review our manuscript and\ngiving valuable suggestion. The core innovation of this work lies in the significant\nbreakthrough achieved in the synthetic strategy for COFs. We successfully applied the\nphotocatalytic four-component reaction for the first time to synthesize a series of novel\nCOFs. This novel approach concurrently integrates the advantages of both photocatalysis\nand four-component reactions, including green and mild reaction conditions, economical\nand efficient synthetic steps, and precise structural control over the resulting COFs.\nMoreover, compared with the widely used traditional solvothermal method, this synthetic\nstrategy can accommodate functional groups or monomers that are unstable under harsh\nconditions, thereby furnishing COFs with enhanced structural diversity and functional\ntunability. Therefore, we believe that this work represents a major breakthrough and\ninnovation at the intersection of materials science and green synthetic methodology, and\nwe sincerely hope it merits your consideration. They have been added in the revised\nmanuscript (please see the abstract section on page 2, and discussion section on page\n14).\nReviewer 3’s comments:\nThe authors have answered most of the questions. One question is whether the as-\nobtained COFs are stable up to 200 °C, TGA data is not enough to make this claim. The\nauthors should test the PXRD at different temperatures.\nResponse: We sincerely appreciate the reviewer for taking time to review our manuscript\nand giving valuable suggestion. As suggested by the reviewer, we have measured the\nPXRD patterns of these COFs at different temperatures as shown below. In situ variable-\ntemperature PXRD patterns were measured on a PANalytical Empyrean3 diffractometer\nequipped with Cu Kα radiation operating at 45 kV and 40 mA with the temperature ranging\nfrom 25 °C to 250 °C and a heating rate of 5 °C/min under vacuum. The thermal stability\nof Cp-tBu-N -COF was evaluated using thermogravimetric analysis (TGA), which revealed\n3\nthat the material remained stable up to 200 C (Fig. 3b). Furthermore, in situ variable-\ntemperature PXRD patterns for Cp-tBu-N -COF were measured. The peaks remained\n3\nunchanged before 200 °C (Supplementary Fig. 11), indicating no thermal degradation of\nthe crystalline structure within this temperature range, which was also consistent with the\nTGA results. They have been added in the revised manuscript (please see lines 1-5 on\npage 8), the Instruments and Materials section of the revised Supplementary Information\n(please see page S3), and Supplementary Figs. 11, 23, 33, and 43 of the revised\nSupplementary Information (please see page S9, S23, S30, and S37).\nSupplementary Fig. 11 In situ variable-temperature PXRD patterns of Cp-tBu-N -COF\n3\nheated from 25 °C to 250 °C under vacuum.\nSupplementary Fig. 23 In situ variable-temperature PXRD patterns of Cy-tBu-N -COF\n3\nheated from 25 °C to 250 °C under vacuum.\nSupplementary Fig. 33 In situ variable-temperature PXRD patterns of Cy-OMe-N -COF\n3\nheated from 25 °C to 250 °C under vacuum.\nSupplementary Fig. 43 In situ variable-temperature PXRD patterns of Cp-F-N -COF\n3\nheated from 25 °C to 250 °C under vacuum."}]

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