Ordered Integration and Heterogenization of Catalysts and Photosensitizers in Metal-/Covalent-Organic Frameworks for Boosting CO2 Photoreduction.

ConspectusSolar-driven CO2 reduction into value-added chemicals, such as CO, HCOOH, CH4, and C2+ products, has been regarded as a potential way to alleviate environmental pollution and the energy crisis. In the past decades, numerous pioneered homogeneous catalytic systems composed of soluble photosensitizers (PSs) and catalytic active sites (CASs) have been explored for CO2 photoreduction. Nevertheless, inefficient electron migration based on random collision between CASs and PSs in homogeneous catalytic systems usually causes mediocre performance. Moreover, the relatively poor separation/recycling capability of the homogeneous systems has inevitably reduced their reusability and practicality. The rational combination of PSs and CASs have been proven to play critical roles in the development of highly efficient heterogeneous catalysts to improve their performance, such as anchoring them onto the solid matrixes or connecting them through bridging ligands. However, developing effective assembly strategies to achieve the ordered orientation and uniform heterogenization of PSs and CASs remains a great challenge, mainly due to the lack of crystallinity heterogeneous transformation and structural tailoring ability of traditional solid catalysts. Moreover, due to the lack of assembly and synthesis strategies, many efficient homogeneous photocatalytic systems are still unable to achieve high crystallinity heterogeneous transformation.Metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) have recently attracted broad interest toward CO2 photocatalysis because of their diverse precursors, well-defined and tailorable structures, abundant exposed CASs and high surface areas, etc. Especially, the highly ordered orientation and uniform combination of PSs and CASs in MOFs and COFs are beneficial for improved light harvesting and charge separation, greatly helping to address the aforementioned challenges. Moreover, the well-defined crystalline structures of MOFs and COFs facilitate the establishment of the structure-activity relationship. Therefore, it is increasingly important to summarize the integration of PSs and catalysts to provide deep insight into MOF/COF-based photocatalysts.In this Account, we summarize the ordered integration of PSs and CASs in MOFs and COFs for CO2 photoconversion and describe the structure-activity relationships to guide the design of effective catalysts. Given the unique structural features of MOFs and COFs, we have emphasized the integration of PSs and CASs to optimize their photocatalytic performance, including the confinement of catalytic active nanoparticles (NPs) into photosensitizing frameworks, co-coordination of PSs and CASs, and ligand-to-metal charge-transfer and anchoring CASs on the secondary building units of the photosensitizing frameworks. The catalytic activity, selectivity, sacrificial agent, and stability of these systems were then discussed. More importantly, MOFs and COFs provide powerful platforms to understand the key steps for boosting CO2 photoreduction and exploring the catalytic mechanism, involving light harvesting, electron-hole separation/migration, and surface redox reactions. Finally, the perspective and challenge of CO2 photoreduction in MOF/COF platforms are further proposed and discussed. It is expected that this Account would provide deep insight into the integration of PSs and catalysts in COFs and MOFs with well-defined structures and afford significant inspiration toward enhanced performance in heterogeneous catalysis.

π-Sticked Metal-Organic Monolayers for Single-Metal-Site Dependent CO2 Photoreduction and Hydrogen Evolution Reaction.

Hierarchical self-assembly of 2D metal-organic layers (MOLs) for the construction of advanced functional materials have witnessed considerable interest, due to the increasing atomic utilizations and well-defined atom-property relationship. However, the construction of atomically precise MOLs with mono-/few-layered thickness through hierarchical self-assembly process remains a challenge, mostly because the elaborate long-range order is difficult to control via conventional noncovalent interaction. Herein, a quadruple π-sticked metal-organic layer (πMOL) is reported with checkerboard-like lattice in ≈1.0 nanometre thickness, on which the catalytic selectivity can be manipulated for highly efficient CO2 reduction reaction (CO2 RR) and hydrogen evolution reaction (HER) over a single metal site. In saturated CO2 aqueous acetonitrile, Fe-πMOL achieves a highly effective CO2 RR with the yield of ≈3.98 mmol g-1  h-1 and 91.7% selectivity. In contrast, the isostructural Co-πMOL as well as mixed metallic FeCo-πMOL exhibits a high activity toward HER under similar conditions. DFT calculations reveal that single metal site exhibits the significant difference in CO2 adsorption energy and activation barrier, which triggers highly selective CO2 RR for Fe site and HER for Co site, respectively. This work highlights the potential of supramolecular π… π interaction for constructing monolayer MOL materials to uniformly distribute the single metal sites for artificial photosynthesis.

CO2 Cycloaddition under Ambient Conditions over Cu-Fe Bimetallic Metal-Organic Frameworks.

Carbon dioxide cycloaddition into fine chemicals is prospective technology to solve energy crisis and environmental issues. However, high temperature and pressure are usually required in the conventional cycloaddition reactions of CO2 with epoxides. Moreover, metal active sites play a vital role in the CO2 cycloaddition, but it is still unclear. Herein, we select the isostructural MOF-919-Cu-Fe and MOF-919-Cu-Al as models to promote the performance and clarify the effects of metal type on the CO2 cycloaddition. The MOF-919-Cu-Fe with exposed Fe and Cu Lewis acid sites reaches the CO2 cycloaddition with over 99.9% conversion and over 99.9% selectivity at room temperature and a 1 bar CO2 atmosphere, 3.0- and 52.6-fold higher than those of the MOF-919-Cu-Al with Al and Cu sites (33.8%) and the 1H-pyrazole-4-carboxylic acid, Fe, and Cu mixed system (1.9%), respectively. The proposed mechanism demonstrated that the exposed Fe3+ sites facilitate the ring opening of epoxide and CO2 activation to boost the CO2 cycloaddition reaction. This work provides a new insight to tune the catalytic sites of MOFs to achieve high performance for CO2 fixation.

Spin Manipulation in a Metal-Organic Layer through Mechanical Exfoliation for Highly Selective CO2 Photoreduction.

Spin manipulation of transition-metal catalysts has great potential in mimicking enzyme electronic structures to improve activity and/or selectivity. However, it remains a great challenge to manipulate room-temperature spin state of catalytic centers. Herein, we report a mechanical exfoliation strategy to in situ induce partial spin crossover from high-spin (s=5/2) to low-spin (s=1/2) of the ferric center. Due to spin transition of catalytic center, mixed-spin catalyst exhibits a high CO yield of 19.7 mmol g-1 with selectivity of 91.6 %, much superior to that of high-spin bulk counterpart (50 % selectivity). Density functional theory calculations reveal that low-spin 3d-orbital electronic configuration performs a key function in promoting CO2 adsorption and reducing activation barrier. Hence, the spin manipulation highlights a new insight into designing highly efficient biomimetic catalysts via optimizing spin state.

Multi-Emission from Single Metal-Organic Frameworks under Single Excitation.

Multi-emission materials have come to prominent attention ascribed to their extended applications other than single-emission ones. General and robust design strategies of a single matrix with multi-emission under single excitation are urgently required. Metal-organic frameworks (MOFs) are porous materials prepared with organic ligands and metal nodes. The variety of metal nodes and ligands makes MOFs with great superiority as multi-emission matrices. Guest species encapsulated into the channels or pores of MOFs are the additional emission sites for multi-emission. In this review, multi-emission MOFs according to the different excitation sites are summarized and classified. The emission mechanisms are discussed, such as antenna effect, excited-state intramolecular proton transfer (ESIPT) and tautomerism for dual-emission. The factors that affect the emissions are revealed, including ligand-metal energy transfer and host-guest interaction, etc. Multi-emission MOFs could be predictably designed and prepared, once the emissive factors are controlled rationally in combination with the different multi-emission mechanisms. Correspondingly, new and practical applications are realized, including but not limited to ratiometric/multi-target sensing and bioimaging, white light-emitting diodes, and anti-counterfeiting. The design strategies of multi-emission MOFs and their extensive applications are reviewed. The results will shed light on other multi-emission systems to develop the structure-derived functionality and applications.

Metal-Organic Frameworks with Multiple Luminescence Emissions: Designs and Applications.

Emissive species are powerful for luminescent detection with high sensitivity and simple procedure and for light-emitting diode (LED) lighting because of their high efficiency, long lifetime, and low energy consumption. Here we propose the concept of multiple luminescence emissions from a single matrix or species under single-wavelength excitation. Multiemission not only realizes the high sensitivity of luminescence sensing but also possesses the capacity of self-reference for environment-free interferences. The color change is also convenient for visible detection. In multiemission species, every emissive center responds to a specific analyte to improve the efficiency for multiple-target detection. Multiemission also extends the applications to anticounterfeiting, colorful LEDs, and information storage. To date, it is still challenging to combine more than one type of emissive center in a single matrix or species. Obtaining multiemission under single-wavelength excitation also needs exquisite design. Metal-organic frameworks (MOFs) are porous hybrid assemblies prepared with metal ions and organic ligands. Metal nodes and ligands with large π-conjugated systems have the potential for the construction of luminescent MOFs. Abundant and diverse precursors provide the possibility to prepare MOFs with multiple luminescence emissions. The pores or channels of MOFs also act as hosts to encapsulate luminescent guest species as additional emissive sites. In this Account, we propose the concept of multiple-luminescence MOFs (ML-MOFs) and summarize the recent research progress on their designs, constructions, and applications reported by our group and others. ML-MOFs are MOFs that possess more than one emissive center under single-wavelength excitation. Six different kinds of construction strategies of ML-MOFs are introduced: (1) multiemission from both metal nodes and ligands in single MOFs; (2) use of mixed-metal nodes as multiemission centers in single MOFs; (3) combination of different emissive MOFs as a whole to achieve multiemission application; (4) host-guest emissions from emissive MOFs after encapsulation of luminescent guest species; (5) organization of different emissive ligands in a single MOF for multiemission; and (6) use of single ligands exhibiting dual emission to prepare ML-MOFs. We also discuss the mechanisms that realize multiple emissions from MOFs under single-wavelength excitation, such as the antenna effect and excited-state intramolecular proton transfer. The applications of ratiometric sensing, LED lighting, anticounterfeiting, and information storage are summarized. With this Account, we hope to spark new ideas and to inspire new endeavors in the design and construction of ML-MOFs, especially with postsynthetic techniques such as postsynthetic modification, postsynthetic exchange, and postsynthetic deprotection, to promote the applications of MOFs in sensing, lighting, information storage, and others.

Rotation Restricted Emission and Antenna Effect in Single Metal-Organic Frameworks.

Aggregation induced-emission (AIE) and antenna effects are important luminescence behaviors. Thus, investigating their emission mechanisms and revealing their behaviors have become critical but challenging. Here we design and prepare metal-organic frameworks (MOFs) with an AIE ligand (i.e., tetrakis(4-carboxyphenyl)pyrazine (L1)) and Ln3+ ions (including Eu3+, Tb3+, and Gd3+). The emission from L1 is gradually enhanced during the formation of the MOFs because coordination restricts the intramolecular rotation. Thus, the emission is called as coordination-induced emission (CIE) with the same restriction of intramolecular rotation mechanism as AIE. Meanwhile, benzene rings twist to adapt to the MOFs' rigid structure, so the emission blueshifts gradually, as an additional evidence of CIE. Both AIE and CIE are "rotation-restricted emission (RRE)". Eu3+ ions exhibit the strongest emission with gradually enhanced intensity during the formation of L1-Eu MOF. Combined with emission properties from Tb3+ and Gd3+ ions, the antenna effect is verified. We also validate the conditions for the efficient sensitization of Ln3+ ions experimentally and refresh the threshold value of the energy gap between triplet state of a ligand and excited state of Ln3+ ions to 3000 cm-1. Thus, RRE and antenna effects are revealed and validated simultaneously. Because CIE of L1 and antenna effect emission from Eu3+ ions are enhanced simultaneously as strong dual emissions, ratiometric fluorescence detection is realized with the detection of arginine as a model. Our results incorporate AIE and CIE into RRE, which provides explicit information for the construction and application of emission systems with AIE ligands as building blocks. MOFs are also extended to explore the emission mechanism and the energy transfer between ligands and metal ions.

Endovascular Denervation: A New Approach for Cancer Pain Relief?

PURPOSE: To evaluate the effects of endovascular denervation (EDN) on abdominal cancer pain relief. MATERIALS AND METHODS: From April 2017 to February 2018, 7 cancer patients (2 males and 5 females) were enrolled in this study. The diagnoses of the patients included 3 pancreatic cancer, 2 cervical carcinoma, 1 cholangiocarcinoma, and 1 esophageal cancer with retroperitoneum lymph nodes invasion. Denervation was carried out at the abdominal aorta close to the origin of celiac artery and superior mesenteric artery with the use of a multielectrode radiofrequency ablation catheter with settings of time 120 seconds and temperature 60°C. The primary end point was improvement in pain scores. The secondary end points included change in quality of life, intake of narcotics, and the safety of EDN. RESULTS: All of the patients experienced pain relief. The pain scores as measured by means of visual analog scores at 1, 2, 4, 8, and 12 weeks after the procedure were significantly lower than before the operation (P < .001). A > 4 score reduction was observed in all cases. A significant reduction in narcotics use within 3 months after the operation was also seen. The quality of life scores of the patients improved significantly (P < .005) with better sleep. No severe treatment-related adverse events or major complications were observed. CONCLUSIONS: EDN is a safe and effective means to alleviate pain caused by cancer and may serve as a new approach for cancer pain relief and palliative care.

Effects of Multi-Electrode Renal Denervation on Insulin Sensitivity and Glucose Metabolism in a Canine Model of Type 2 Diabetes Mellitus.

PURPOSE: To evaluate the effects of multi-electrode catheter-based renal denervation (RDN) on insulin sensitivity and glucose metabolism in a type 2 diabetes mellitus (T2DM) canine model. MATERIALS AND METHODS: Thirty-three dogs were divided equally into 3 groups: bilateral renal denervation (BRDN) group, left renal denervation (LRDN) group, and sham operation (SHAM) group. Body weight and blood biochemistry were measured at baseline, 20 weeks, and 32 weeks, and renal angiography and computerized tomographic (CT) angiography were determined before the procedure and 1 month, 2 months, and 3 months after the procedure. Western blot was used to identify the activities of gluconeogenic enzymes and insulin-signaling proteins. RESULTS: Fasting plasma glucose (9.64 ± 1.57 mmol/L vs 5.12 ± 1.08 mmol/L; P < .0001), fasting insulin (16.19 ± 1.43 mIU/mL vs 5.07 ± 1.13 mIU/mL; P < .0001), and homeostasis-model assessment of insulin resistance (HOMA-IR; 6.95 ± 1.33 vs 1.15 ± 0.33; P < .0001) in the BRDN group had significantly decreased at the 3-month follow-up compared with the SHAM group. Western blot analyses showed that RDN suppressed the gluconeogenetic genes, modulated insulin action, and activated insulin receptors-AKT signaling cascade in the liver. CT angiography and histopathologic analyses did not show any dissection, aneurysm, thrombus, or rupture in any of the renal arteries. CONCLUSIONS: These findings identified that multi-electrode catheter-based RDN could effectively decrease gluconeogenesis and glycogenolysis, resulting in improvements in insulin sensitivity and glucose metabolism in a T2DM canine model.

Ratiometric Fluorescence Sensing and Real-Time Detection of Water in Organic Solvents with One-Pot Synthesis of Ru@MIL-101(Al)-NH2.

Ratiometric fluorescence detection attracts much attention because of its decreased environmental influence and easy-to-differentiate color and intensity change. Herein, a guest-encapsulation metal-organic framework (MOF), Ru@MIL-NH2, is prepared with 2-aminoterephthalic acid, AlCl3, and Ru(bpy)32+ by a simple one-pot method for ratiometric fluorescence sensing of water in organic solvents. The rational selection of the excitation wavelength provides dual emission at 465 and 615 nm from Ru@MIL-NH2 under a single excitation of 300 nm. High sensitivity, low detection limit (0.02% v/v), wide response range (0-100%), and fast response (less than 1 min) are obtained for ratiometric fluorescence sensing of water under single excitation with Ru@MIL-NH2 as the probe. Moreover, the result of water content is independent of the concentration of Ru@MIL-NH2 as the merit of ratiometric fluorescence detection. The response mechanism reveals that the protonation of the nitrogen atom of the MIL-NH2, the π-conjugation system, and the stable fluorescence of Ru(bpy)32+ achieve the ratiometric fluorescence. The analysis of real spirit samples confirms the proposed method. A test strip is prepared with Ru@MIL-NH2 for convenient use. We believe that such turn-on ratiometric host-guest MOFs and the rational selection of excitation wavelength will offer guidance for ratiometric fluorescence detection with wide applications.

Single Dispersion of Fe(H2O)2-Based Polyoxometalate on Polymeric Carbon Nitride for Biomimetic CH4 Photooxidation.

Direct methane conversion to value-added oxygenates under mild conditions with in-depth mechanism investigation has attracted wide interest. Inspired by methane monooxygenase, the K9Na2Fe(H2O)2{[γ-SiW9O34Fe(H2O)]}2·25H2O polyoxometalate (Fe-POM) with well-defined Fe(H2O)2 sites is synthesized to clarify the key role of Fe species and their microenvironment toward CH4 photooxidation. The Fe-POM can efficiently drive the conversion of CH4 to HCOOH with a yield of 1570.0 µmol gPOM -1 and 95.8% selectivity at ambient conditions, much superior to that of [Fe(H2O)SiW11O39]5- with Fe(H2O) active site, [Fe2SiW10O38(OH)]2 14- and [P8W48O184Fe16(OH)28(H2O)4]20- with multinuclear Fe-OH-Fe active sites. Single-dispersion of Fe-POM on polymeric carbon nitride (PCN) is facilely achieved to provide single-cluster functionalized PCN with well-defined Fe(H2O)2 site, the HCOOH yield can be improved to 5981.3 µmol gPOM -1. Systemic investigations demonstrate that the (WO)4-Fe(H2O)2 can supply Fe═O active center for C-H activation via forming (WO)4-Fea-Ot···CH4 intermediate, similar to that for CH4 oxidation in the monooxygenase. This work highlights a promising and facile strategy for single dispersion of ≈1-2 Å metal center with precise coordination microenvironment by uniformly anchoring nanoscale molecular clusters, which provides a well-defined model for in-depth mechanism research.

W Single-Atom Catalyst for CH4 Photooxidation in Water Vapor.

Solar-driven high-efficiency and direct conversion of methane into high-value-added liquid oxygenates against overoxidation remains a great challenge. Herein, facile and mass fabrication of low-cost tungsten single-atom photocatalysts is achieved by directly calcining urea and sodium tungstate under atmosphere (W-SA-PCN-m, urea amount m = 7.5, 15, 30, and 150 g). The single-atom photocatalysts can manage H2 O2 in situ generation and decomposition into ·OH, thus achieving highly efficient CH4 photooxidation in water vapor under mild conditions. Systematic investigations demonstrate that integration of multifunctions of methane activation, H2 O2 generation, and decomposition into one photocatalyst can dramatically promote methane conversion to C1 oxygenates with a yield as high as 4956 µmol gcat -1 , superior to that of the most reported non-precious photocatalysts. Liquid-solid phase transition can induce the products to facilely switch in from HCOOH to CH3 OH by pulling the catalyst above water with CH3 OH/HCOOH ratio from 10% (in H2 O) to 80% (above H2 O).

A switchable sensor and scavenger: detection and removal of fluorinated chemical species by a luminescent metal-organic framework.

Fluorosis has been regarded as a worldwide disease that seriously diminishes the quality of life through skeletal embrittlement and hepatic damage. Effective detection and removal of fluorinated chemical species such as fluoride ions (F-) and perfluorooctanoic acid (PFOA) from drinking water are of great importance for the sake of human health. Aiming to develop water-stable, highly selective and sensitive fluorine sensors, we have designed a new luminescent MOF In(tcpp) using a chromophore ligand 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine (H4tcpp). In(tcpp) exhibits high sensitivity and selectivity for turn-on detection of F- and turn-off detection of PFOA with a detection limit of 1.3 µg L-1 and 19 µg L-1, respectively. In(tcpp) also shows high recyclability and can be reused multiple times for F- detection. The mechanisms of interaction between In(tcpp) and the analytes are investigated by several experiments and DFT calculations. These studies reveal insightful information concerning the nature of F- and PFOA binding within the MOF structure. In addition, In(tcpp) also acts as an efficient adsorbent for the removal of F- (36.7 mg g-1) and PFOA (980.0 mg g-1). It is the first material that is not only capable of switchable sensing of F- and PFOA but also competent for removing the pollutants via different functional groups.

MOF@COFs with Strong Multiemission for Differentiation and Ratiometric Fluorescence Detection.

Aggregation-caused quenching (ACQ) is often observed in covalent organic frameworks (COFs) for their low emission. Here, we propose that limited COF layers form on UiO-66 to eliminate the ACQ by the formation of UiO@COF composites. UiO-66 is selected because this metal-organic framework (MOF) is easily prepared in nanosize with Zr4+ ion and 2-aminoterephthalic acid (BDC-NH2). The high affinity of the Zr4+ ion to phosphate species improves sensing selectivity. The surface -NH2 reacts with 2,4,6-triformylphloroglucinol (Tp) to integrate COF1 and COF2, which are prepared with Tp and phenylenediamine or tetraamino-tetraphenylethylene, respectively. The hydrogen bond formed between the hydroxyl group in Tp and imine nitrogen realizes excited-state intramolecular proton transfer; therefore, multiemission is observed from the enol and keto states of the COFs and UiO-66 at 360, 470, and 613 nm for UiO@COF1 and at 370, 470, and 572 nm for UiO@COF2. When phosphate ion is added in the composites, the emissions from the COFs keep stable, while that from UiO-66 is enhanced. However, adenosine-5'-triphosphate (ATP) improves the emissions from UiO-66 and COF's enol state, but that from the keto state keeps stable. The differentiation and ratiometric fluorescence detection of ATP and phosphate ion are therefore realized with the multiemission, the affinity of Zr4+ ions, and the structural selectivity of the COFs. Thus, UiO@COF is a novel strategy to integrate multiemission, affinity, and structural selectivity to improve the sensing performance for differentiation and ratiometric detection.

Computed Tomography Imaging-Guided Tandem Catalysis-Enhanced Photodynamic Therapy with Gold Nanoparticle Functional Covalent Organic Polymers.

Tandem catalysis from hydrogen peroxide (H2O2) to oxygen (O2) and then to singlet oxygen (1O2) is a convenient way to overcome the hypoxic environment of the tumor for efficient cancer therapy. In this work, meso-tetrakis(4-carboxyl)-21H,23H-porphine (TCPP) and ß-cyclodextrin (ß-CD) functional gold nanoparticles (CD-AuNPs) are integrated together with a brushy covalent organic polymer (COP-8) to form COP@Au@TCPP nanocomposites. The brushy red emissive COP-8 was prepared with 9,9-dioctyl-2,7-diaminofluorene and 2,4,6-triformylphloroglucinol through a simple Schiff base reaction and acts as a sensor to monitor the material transfer and location in tumor cells. The n-octyl groups on the surface of COP-8 act as hooks to load CD-AuNPs via hydrophobic interaction, while the ß-CD improves the biocompatibility of the whole COP@Au@TCPP. The COP@Au@TCPP nanocomposites aggregate efficiently in the tumor site through enhanced permeability and retention effect. The CD-AuNPs act as catalyzers to decompose H2O2 into O2 in tumor cells. Then, TCPPs on COP@Au@TCPP sensitize O2 to form 1O2 under 655 nm radiation for efficient photodynamic therapy (PDT). In combination with the X-ray computed tomography (CT) imaging capacity of CD-AuNPs, the CT-imaging-guided PDT system was successfully prepared. The imaging information, in turn, shows the tandem catalysis PDT efficiency of the COP@Au@TCPP. This work paves the way for the preparation of an imaging-guided therapy system with COP as a matrix to ingrate various biocompatibility components.

Strong dual emission in covalent organic frameworks induced by ESIPT.

Here we reveal the effects of hydrogen bonds and alkyl groups on the structure and emission of covalent organic frameworks (COFs). Hydrogen bonds improve molecular rigidity leading to high crystallinity and restrict intramolecular rotation to enhance the emission of COFs. An excited-state intramolecular proton transfer (ESIPT) effect for dual emission is achieved via the intramolecular hydrogen bonds between hydroxyl groups and imine bonds. Alkyl groups increase interlayer spacing as a natural "scaffold" and achieve a staggered AB stacking mode to decrease aggregation-caused quenching. Based on the above guidance, COF-4-OH with strong emission is prepared with 2,4,6-triformylphloroglucinol (TFP) and 9,9-dibutyl-2,7-diaminofluorene (DDAF). Strong dual emission is observed and used to differentiate organic solvents with different polarities, to determine the water content in organic solvents, and to detect different pH levels. Our work serves as a guide for the rational design of functional monomers for the preparation of emissive COFs.