Nonlinear Optical Switching in Regioregular Porphyrin Covalent Organic Frameworks

Combining Ti4(embonate)6 anionic cages and π-conjugated coordination cations for highly effective optical limiting

The integration of anionic Ti4L6 (L = embonate) cages and π-conjugated coordination cations into ordered structures can produce high-performance nonlinear optical (NLO) materials. More specifically, by employing Ti4L6 cages for assembly with mixed N,N-chelated and P,P-chelated type conjugated organic ligands and Ag+ ions, three cage-based structures have been synthesized and structurally characterized. Among them, an ion pair structure with strong π-π accumulation exhibits a significant third-order NLO response, and an excellent optical limiting effect has been experimentally verified. This work provides a promising material for NLO applications.

Structurally influenced optical nonlinearities and ultrafast dynamics in β-acroleyl- and β-dicyanobutadienyl-appended cobalt corroles

The strong two-photon induced nonlinear absorption and self-focusing type positive nonlinear refraction are pronounced by the structural engineering in β-functionalized cobalt corroles.

Octupolar Cyclotriphosphazene-Cored Self-Standing Covalent Organic Framework Membranes as Nonlinear Optical Materials: Impact of Linkage Types and Material Forms

Conjugated and processable self-standing vinylene-linked covalent organic framework membranes (COFMs) are highly demanding for photonics and optoelectronics. In this work, we have fabricated the first cyclotriphosphazene (CTP) cored vinylene-linked self-standing COFM (CTP-PDAN). For comparison purposes, we have successfully fabricated the imine-linked congener (CTP-PDA). Leveraging the inherent nonlinear optical (NLO) response of the CTP core, both membranes were directly mounted to evaluate NLO parameters using the open-aperture (OA) Z-scan technique. Direct measurement of NLO responses on membranes is advantageous and free from solvent and scattering effects, making it a more practical approach compared to the conventional dispersion mode. The OA Z-scan transmission yields a reverse saturable absorption signature exhibiting a higher NLO absorption coefficient (β) of 58.37 cm/GW for CTP-PDAN, compared to that of the imine-linked CTP-PDA COFM (β = 8.5 cm/GW). These results can be correlated to the efficient conjugation through the vinylene linkage in CTP-PDAN compared to the imine linked congener.

Ingenious Modulation of Third-Order Nonlinear Optical Response of Zr-MOFs through Defect Engineering Based on a Mixed-Linker Strategy

Defect engineering plays a pivotal role in regulating electronic structure and facilitating charge transfer, yielding captivating effects on third-order nonlinear optical (NLO) properties. In this work, we utilized a mixed-linker strategy to intentionally disrupt the initial periodic arrangement of UiO-66 and construct defects. Specifically, we incorporated tetrakis(4-carboxyphenyl)porphyrin (TCPP) with an exceptionally electron-rich delocalization system into the framework of UiO-66 using a one-pot solvothermal method, ingeniously occupying the partial distribution sites of the Zr6 clusters. Compared to UiO-66, the NLO absorption and refraction performance of TCPP/UiO-66 were significantly improved. Additionally, due to the presence of nitrogen-rich sites that can accommodate metal ions in the porphyrin ring of TCPP, Co(II), Ni(II), Cu(II), and Zn(II) are introduced into TCPP/UiO-66, extending the d-π conjugation effect to further regulate the defects. The NLO absorption behavior transforms saturation absorption (SA) to reverse saturation absorption (RSA), while the refraction behavior shifts from self-defocusing to self-focusing. This work shows that defects can effectively regulate the electronic structure, while TCPP plays a crucial role in significantly enhancing electron delocalization.

Terahertz Conductivity of Free-Standing 3D Covalent Organic Framework Membranes Fabricated via Triple-Layer-Dual Interfacial Approach

Processable covalent organic framework membranes (COFM) are emerging as potential semiconducting materials for device applications. Nevertheless, the fabrication of crystalline and free-standing 3D COFMs is challenging. In this work, a unique time and solvent-efficient triple-layer-dual interfacial (TLDI) approach for the simultaneous synthesis of two 3D COFMs from a single system is developed. Besides, for the first time, the optical conductivity of these free-standing 3D COFMs is analyzed using terahertz (THz) spectroscopy in transmission mode. Interestingly, these membranes show excellent transmittance at THz frequencies with very high intrinsic THz conductivities. The evaluated scattering time and plasma frequency of the free carriers of the COFMs are highly promising for future applications in optoelectronic devices in THz frequencies.

Pseudotetrahedral Organotin-Capped Chalcogenidometalate Supermolecules with Optical Limiting Performance

The rational design of crystalline clusters with adjustable compositions and dimensions is highly sought after but quite challenging as it is important to understand their structural evolution processes and to systematically establish structure-property relationships. Herein, a family of organotin-based sulfidometalate supertetrahedral clusters has been prepared via mixed metal and organotin strategies at low temperatures (60-120 °C). By engineering the metal composition, we can effectively control the size of the clusters, which ranges from 8 to 35, accompanied by variable configurations: P1-[(RSn)4M4S13], T3-[(RSn)4In4M2S16] (R = nbutyl-Bu and phenyl-Ph; M = Cd, Zn, and Mn), T4-[(BuSn)4In13Cu3S31], truncated P2, viz. TP2-[(BuSn)6In10Cu6S31], and even T5-[(BuSn)4In22Zn6Cu3S52], all of which are the largest organometallic supertetrahedral clusters known to date. Of note, the arylstannane approach plays a critical role in regulating the peripheral ligands and further enriching geometric structures of the supertetrahedral clusters. This is demonstrated by the formation of tin-oxysulfide clusters, such as T3-[(RSn)4Sn6O4S16] (R = Bu, Ph, and benzyl = Be) and its variants, truncated T3, viz., TT3-[(BuSn)6Sn3O4S13] and augmented T3, viz., T3-[(Bu3SnS)4Sn6O4S16]. Especially, two extraordinary truncated clusters break the tetrahedral symmetry observed in typical supertetrahedral clusters, further substantiating the advantages offered by the arylstannane approach in expanding cluster chemistry. These organometallic supertetrahedral clusters are highly soluble and stable in common solvents. Additionally, they have tunable third-order nonlinear optical behaviors by controlling the size, heterometallic combination, organic modification, and intercluster interaction.

Porphyrin-Based Conjugated Microporous Polymer Loaded with Nanoscale Zerovalent Iron for the Degradation of Organic Pollutants under Visible Light

The degradation of organic dye from waterbodies is of great significance for clean production and environmental remediation. Herein, two porphyrin-based conjugated microporous polymers (CMPs) loaded with nanoscale zerovalent iron (named as Por-CMPs-1-2@nZVI) were successfully fabricated by Sonogashira-Hagihara coupling reactions and the liquid-phase method. The as-synthesized Por-CMPs-1-2@nZVI composites were characterized by various means of analysis, and it was confirmed that Por-CMPs-1-2 loaded with nZVI had good photocatalytic performance. Calculated by ultraviolet-visible spectrum, the band-gap energies of Por-CMPs-1@nZVI and Por-CMPs-2@nZVI were 1.45 and 1.32 eV, respectively, indicating that both can be activated by visible light. The photodegradation of organic dye experiments demonstrated that Por-CMPs-2@nZVI degraded 98.0% of 10 ppm Methylene Blue (MB) within 150 min, which is higher than that of Por-CMPs-1-2 and Por-CMPs-1@nZVI. The experiment of active substance capture and mechanism of ESR confirmed that superoxide anion and hydroxyl radical were the primary valid substances in the photodegradation process of MB. In addition, the preparation of membrane materials was shown to be a successful strategy to realize engineered scale-up production.

Stacked Covalent Organic Ribbons Perpendicular to Graphene Oxide Sheets; a 1D-p-2D Design for Photocatalytic Tandem Reactions

Development of one dimensional covalent organic frameworks (1D-COFs) with potential in light absorption and catalysis is still challenging, due to their rapid interpenetration to form 2D and 3D porous structures. Here we report a successful synthesis of imine-linked 1D covalent organic ribbons (COR), using two simple linear building blocks 1,4-Benzenediamine (Bda) and [2,2'-Bipyridine]-5,5'-dicarbaldehyde (Bpy). The obtained 1D structure with nanorod morphology could keep its physicochemical characteristic properties when it is perpendicular to the surface of graphene oxide (GO) sheets (1D-p-2D structure). Due to an AB π- π stacking and efficient charge transfer between perpendicular 1D COR and GO sheets, the obtained nanocomposite showed strong visible light absorbance (400-700 nm) with coefficient of 4.400 M-1  cm-1 and decreased recombination rate of photogenerated reactive species by 92 %. The strategy of 1D-p-2D light driven system greatly enhanced the photocatalytic activity in practical applications such as both oxidation and hydrogenation tandem reactions to a rate constant of higher than 0.02 min-1 . This study presents the first case of 1D covalent organic polymers grown perpendicularly on a carbon-based layer for boosting electron mobility through the junction between the two components.

Fabrication of Two-Dimensional Homo-Bimetallic Porphyrin Framework Thin Films for Optimizing Nonlinear Optical Limiting

Developing efficient metal-organic framework (MOF) optical devices with tunable third-order nonlinear optical (NLO) properties is an important challenge for scientific research and practical application. Herein, 2D monometallic and hetero/homo-bimetallic porphyrin MOF thin films (ZnTCPP(M) M = H2, Fe, Zn) were fabricated using the liquid-phase epitaxial (LPE) layer-by-layer (LBL) method to investigate the metal substitution dependent third-order NLO behavior. The prepared homo-bimetallic ZnTCPP(Zn) thin film exhibited enhanced third-order NLO performance with a higher third-order nonlinear susceptibility of ∼4.21 × 10-7 esu compared to monometallic and hetero-bimetallic counterparts. Additionally, theoretical calculations were performed to complement the experimental findings and revealed that the enhanced NLO effect of the ZnTCPP(Zn) thin film is mainly attributed to the enhanced local excitation. These findings not only provide a comprehensive understanding of the relationship between metal types and the NLO behavior of porphyrin MOF thin films but also offer valuable insights into the design and optimization of NLO devices.

Porphyrin-based covalent organic polymers with customizable photoresponses for photodynamic inactivation of bacteria

Porphyrin-linked covalent organic polymers (COPs) provide a reliable photocatalytic platform, while photodynamic inactivation (PDI) induced by reliable porphyrin-based COPs is considered to be an effective method to resist microbial contamination. Herein, three tunable porphyrin-based covalent organic polymers (H2-Por-COPs, OH-Por-COPs, and Zn-Por-COPs) are designed and employed for the PDI of Staphylococcus aureus and Escherichia coli under visible light illumination. Interestingly, singlet oxygen (1O2) generation by the Por-COPs can be manipulated via intramolecular regulation with the order Zn-Por-COP > OH-Por-COP > H2-Por-COP. With rationally tune, the Zn-Por-COP demonstrated remarkable antibacterial activity against Staphylococcus aureus (kill percentage 99.65 % ± 0.24 %) and Escherichia coli (kill percentage 97.25 % ± 1.78 %) in only 15 min under visible-light irradiation. Density functional theory (DFT) calculations and photophysical tests showed that the presence of electron-donating -OH groups on the aromatic linkers and Zn2+ ions in porphyrin units narrowed the HOMO-LUMO gap, enhancing both light absorption, intersystem crossing (ISC) and 1O2 generation for more efficient bacteria inactivation. This work can be applied to efficiently screen suitable photosensitizers and provides a rational regulatory strategy for PDI of pathogenic bacteria.

Green synthesis of bifunctional phthalocyanine-porphyrin cofs in water for efficient electrocatalytic CO2 reduction coupled with methanol oxidation

Electrocatalytic CO2 reduction (ECR) coupled with organic oxidation is a promising strategy to produce high value-added chemicals and improve energy efficiency. However, achieving the efficient redox coupling reaction is still challenging due to the lack of suitable electrocatalysts. Herein, we designed two bifunctional polyimides-linked covalent organic frameworks (PI-COFs) through assembling phthalocyanine (Pc) and porphyrin (Por) by non-toxic hydrothermal methods in pure water to realize the above catalytic reactions. Due to the high conductivity and well-defined active sites with different chemical environments, NiPc-NiPor COF performs efficient ECR coupled with methanol oxidation reaction (MOR) (Faradaic efficiency of CO (FECO) = 98.12%, partial current densities of CO (jCO) = 6.14 mA cm-2 for ECR, FEHCOOH = 93.75%, jHCOOH = 5.81 mA cm-2 for MOR at low cell voltage (2.1 V) and remarkable long-term stability). Furthermore, experimental evidences and density functional theory (DFT) calculations demonstrate that the ECR process mainly conducts on NiPc unit with the assistance of NiPor, meanwhile, the MOR prefers NiPor conjugating with NiPc. The two units of NiPc-NiPor COF collaboratively promote the coupled oxidation-reduction reaction. For the first time, this work achieves the rational design of bifunctional COFs for coupled heterogeneous catalysis, which opens a new area for crystalline material catalysts.

Ni(II)-Incorporated Ethylene Glycol-Linked Tetraphenyl Porphyrin-Based Covalent Organic Polymer as a Catalyst for Methanol Electrooxidation

Methanol oxidation reaction (MOR) is a perfect alternative to the conventional oxygen evolution reaction (OER), generally utilized as the anode reaction for hydrogen generation via the electrochemical water splitting method. Moreover, MOR is also relevant to direct methanol fuel cells (DMFCs). These facts motivate the researchers to develop economical and efficient electrocatalysts for MOR. Herein, we have introduced an ethylene glycol-linked tetraphenyl porphyrin-based (EG-POR) covalent organic polymer (COP). The Ni(II)-incorporated EG-POR material Ni-EG-POR displayed excellent OER and MOR activities in an alkaline medium. The materials were thoroughly characterized using 13C solid-state NMR, Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) surface area analyzer, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermogravimetric analyzer (TGA), and powder X-ray diffraction (PXRD) techniques. These organic-inorganic hybrid materials showed high chemical and thermal stability. Ni-EG-POR requires an overpotential of 400 mV (vs RHE) in OER and 190 mV (vs RHE) in MOR to achieve a current density of 10 mA cm-2. In addition, the catalyst also showed excellent chronoamperometric and chronopotentiometric stability, indicating that the catalyst can provide stable current over a longer period and its potential as a non-noble metal MOR catalyst.

Structure determination of a low-crystallinity covalent organic framework by three-dimensional electron diffraction

Covalent organic frameworks (COFs) have been attracting intense research due to their permanent porosity, designable architecture, and high stability. However, COFs are challenging to crystallize and their synthesis often results in tiny crystal sizes and low crystallinities, which hinders an unambiguous structure determination. Herein, we demonstrate that the structure of low-crystallinity COF Py-1P nanocrystals can be solved by coupling three-dimensional electron diffraction (3DED) with simulated annealing (SA). The resulting model is comparable to that obtained from high-crystallinity samples by dual-space method. Moreover, for low-resolution 3DED data, the model obtained by SA shows a better framework than those provided by classic direct method, dual-space method, and charge flipping. We further simulate data with different resolutions to understand the reliability of SA under different crystal quality conditions. The successful determination of Py-1P structure by SA compared to other methods provides new knowledge for using 3DED to analyze low-crystallinity and nanosized materials.

2D Covalent Organic Frameworks Based on Heteroacene Units

Covalent organic frameworks (COFs) are a unique new class of porous materials that arrange building units into periodic ordered frameworks through strong covalent bonds. Accompanied with structural rigidity and well-defined geometry, heteroacene-based COFs have natural advantages in constructing COFs with high stability and crystallinity. Heteroacene-based COFs usually have high physical and chemical properties, and their extended π-conjugation also leads to relatively low energy gap, effectively promoting π-electron delocalization between network units. Owing to excellent electron-withdrawing or -donating ability, heteroacene units have incomparable advantages in the preparation of donor-acceptor type COFs. Therefore, the physicochemical robust and fully conjugated heteroacene-based COFs solve the problem of traditional COFs lacking π-π interaction and chemical stability. In recent years, significant breakthroughs are made in this field, the choice of various linking modes and building blocks has fundamentally ensured the final applications of COFs. It is of great significance to summarize the heteroacene-based COFs for improving its complexity and controllability. This review first introduces the linkages in heteroacene-based COFs, including reversible and irreversible linkages. Subsequently, some representative building blocks are summarized, and their related applications are especially emphasized. Finally, conclusion and perspectives for future research on heteroacene-based COFs are presented.

Covalent Organic Frameworks as Emerging Nonlinear Optical Materials

The vastness of organic synthetic strategies and knowledge of reticular chemistry have made covalent organic frameworks (COFs) one of the most chemically and structurally diverse class of materials with potential applications ranging from gas storage, molecular separation, and catalysis to energy storage and magnetism. Recently, this class of porous materials has garnered increasing interest as potential nonlinear optical (NLO) materials. Traditionally, inorganic crystals, small-molecule organic chromophores, and oligomers have been studied for their NLO response. Nevertheless, COFs offer significant advantages over existing NLO materials in terms of higher mechanical strength, thermochemical stability, and extended conjugation. Herein, we discuss crucial aspects, terminology, and measurement techniques related to NLO, followed by a critical analysis of the design principles for COFs with NLO response. Furthermore, we touch on selected potential applications of these NLO materials. Finally, future prospects and challenges of COFs as NLO materials are discussed.

In Situ Interweaved High Sulfur Loading Li-S Cathode by Catalytically Active Metalloporphyrin Based Organic Polymer Binders

The elaborate design of powerful Li-S binders with extended-functions like polysulfides adsorption/catalysis and Li⁺ hopping/transferring in addition to robust adhesion-property has remained a challenge. Here, an in situ cathode-interweaving strategy based on metalloporphyrin based covalent-bonding organic polymer (M-COP, M = Mn, Ni, and Zn) binders is reported for the first time. Thus-produced functional binders possess excellent mechanical-strengths, polysulfides adsorption/catalysis, and Li⁺ hopping/transferring ability. Specifically, the modulus of Mn-COP can reach up to ≈54.60 GPa (≈40 times higher than poly(vinylidene fluoride)) and the relative cell delivers a high initial-capacity (1027 mAh g^-1 , 1 C and 913 mAh g^-1 , 2 C), and excellent cycling-stability for >1000 cycles even at 4 C. The utilization-rate of sulfur can reach up to 81.8% and the electrodes based on these powerful binders can be easily scale-up fabricated (≈20 cm in a batch-experiment). Noteworthy, Mn-COP based cell delivers excellent capacities at a high sulfur-loading (8.6 mg cm^-2 ) and low E/S ratio (5.8 µL mg^-1 ). In addition, theoretical calculations reveal the vital roles of metalloporphyrin and thiourea-groups in enhancing the battery-performance.

Enhanced non-linear optical properties of porphyrin-based polymers covalently functionalized with graphite phase carbon nitride

In our work, a flurry of original porphyrin-based polymers covalently functionalized g-C₃N₄ nanohybrids were constructed and nominated as PPorx-g-C₃N₄ (x = 1, 2 and 3) through click chemistry between porphyrin-based polymers with alkyne end-groups [(PPorx-C≡CH (x = 1, 2 and 3)] and azide-functionalized graphitic carbon nitride (g-C₃N₄-N₃). Due to the photoinduced electron transfer (PET) between porphyrin-based polymers [PPorx (x = 1, 2 and 3)] group and graphite phase carbon nitride (g-C₃N₄) group in PPorx-g-C₃N₄ nanohybrids, the PPorx-g-C₃N₄ nanohybrids exhibited better non-linear optical (NLO) performance than the corresponding PPorx-C≡CH and g-C₃N₄-N₃. It found that the imaginary third-order susceptibility (Im [χ⁽³⁾]) value of the nanohybrids with different molecular weight (MW) of the pPorx group in the nanohybrids ranged from 2.5×10³ to 7.0 × 10³ g mol^-1 was disparate. Quite interestingly, the Im [χ⁽³⁾] value of the nanohybrid with a pPorx group's MW of 4.2 × 10³ g mol^-1 (PPor2-g-C₃N₄) was 1.47 × 10^-10 esu, which exhibited the best NLO performance in methyl methacrylate (MMA) of all nanohybrids. The PPorx-g-C₃N₄ was dispersed in polymethyl methacrylate (PMMA) to prepare the composites PPorx-g-C₃N₄/PMMA since PMMA was widely used as an alternative to glass. PPor2-g-C₃N₄/PMMA showed the excellent NLO performance of all nanohybrids with the Im [χ⁽³⁾] value of 2.36 × 10^-10 esu, limiting threshold of 1.71 J/cm², minimum transmittance of 8% and dynamic range of 1.09 in PMMA, respectively. It suggested that PPorx-g-C₃N₄ nanohybrids were potential outstanding NLO materials.

Construction of Atomic Metal-N2 Sites by Interlayers of Covalent Organic Frameworks for Electrochemical H2 O2 Synthesis

Electrosynthesis of H₂ O₂ is a promising alternative to the anthraquinone oxidation process because of its low energy utilization and cost-effectiveness. Heteroatom-doped carbons-based catalysts have been widely developed for H₂ O₂ synthesis. However, their doping degree, defective degree, and location of active sites are difficult to be preciously controlled at molecular level. Herein, a dioxin-linked covalent organic framework (COF) is used as the template to preciously construct different metal-N₂ sites along the porous walls for H₂ O₂ synthesis. By tuning the metal centers, the catalyst with Ca-N₂ sites enables to catalyze H₂ O₂ production with selectivity over 95% from 0.2 to 0.6 V versus RHE, while the H₂ O₂ yields for Co sites or Ni sites are 20% and 60% in the same potential range. In addition, the turnover frequency (TOF) values for Ca-N₂ sites are 11.63 e^-1 site^-1 s^-1 , which are 58 and 20 times higher than those of Co and Ni sites (0.20 and 0.57 e^-1 site^-1 s^-1 ). The theoretical calculations further reveal that the OOH* desorption on Ca sites is easier than those on Co or Ni sites, and thus catalyzes the oxygen reduction reaction in the 2e^- pathway with high efficiency.

Zn (II) Porphyrin Built-in D-A Covalent Organic Framework for Efficient Photocatalytic H2 Evolution

Covalent organic frameworks (COFs) with donor-acceptor (D-A) units are credible photocatalysts for their per-designed structure, inherent porosity, large surface area, splendid stability and so forth. Developing COFs with an excellent photocatalytic efficiency for hydrogen evolution is of a great significance in alleviating the energy crisis. Herein, a D-A type imine-linked crystalline Zn-Por-TT COF was fabricated successfully via the co-polymerization of electron-deficient Zinc (II) 5,10,15,20-tetrakis(para-aminophenyl) porphyrin (Zn-TAPP), and electron-rich thieno[3,2-b]thiophene-2,5-dicarbaldehyde (TT). Profiting from the D-A complex structure, the obtained Zn-Por-TT COF showcases an excellent photocatalytic activity with a hydrogen evolution rate of 8200 μmol/g/h, while the Zn-TAPP monomer presents practically no capacity for the generation of hydrogen under identical conditions. In addition, the counterparts Por-TT COF and COF-366-Zn were employed to illustrate the enhancement of the photocatalytic performance by metal catalytic sites and D-A structures. In addition, the counterparts Por-TT COF and COF-366-Zn were employed to illustrate the enhancement of metal catalytic sites and D-A structures for the photocatalytic performance.

Degradable Multifunctional Porphyrin-Based Porous Organic Polymer Nanosonosensitizer for Tumor-Specific Sonodynamic, Chemo- and Immunotherapy

Sonodynamic therapy (SDT) benefiting from its intrinsic merits, such as noninvasiveness and deep tissue penetrability, is receiving increasing considerable attention in reactive oxygen species (ROS)-based tumor treatment. However, current sonosensitizers usually suffer from low tumor lesion accumulation, insufficient ROS generation efficiency under ultrasound, and non-biodegradability, which seriously impede the therapeutic outcomes. Additionally, it is difficult that SDT alone can completely eradicate tumors because of the complex and immunosuppressive tumor microenvironment (TME). Herein, we simultaneously employ sonosensitive porphyrin building blocks and glutathione (GSH)-responsive disulfide bonds to construct a novel degradable multifunctional porphyrin-based hollow porous organic polymer (POP) nanosonosensitizer (H-Pys-HA@M/R), which combine SDT, "on-demand" chemotherapy, and immunotherapy. Taking the unique advantages of POPs with designable structures and high specific surface area, this H-Pys-HA@M/R nanosonosensitizer can achieve tumor target accumulation, GSH-triggered drug release, and low-frequency ultrasound-activating ROS generation with encouraging results. Furthermore, this multifunctional nanosonosensitizer can effectively evoke immunogenic cell death (ICD) response through the combination of SDT and chemotherapy for both primary and distal tumor growth suppression. Meanwhile, H-Pys-HA@M/R exhibits favorable biodegradation and biosafety. Therefore, this study provides a new strategy for reasonably designing and constructing POP-related sonosensitizers combining SDT/chemotherapy/immunotherapy triple treatment modalities to eradicate malignant tumors.

Atomically Thin, Ionic-Covalent Organic Nanosheets for Stable, High-Performance Carbon Dioxide Electroreduction

The incorporation of charged functional groups is effective to modulate the activity of molecular complexes for the CO₂ reduction reaction (CO₂ RR), yet long-term heterogeneous electrolysis is often hampered by catalyst leaching. Herein, an electrocatalyst of atomically thin, cobalt-porphyrin-based, ionic-covalent organic nanosheets (CoTAP-iCONs) is synthesized via a post-synthetic modification strategy for high-performance CO₂ -to-CO conversion. The cationic quaternary ammonium groups not only enable the formation of monolayer nanosheets due to steric hindrance and electrostatic repulsion, but also facilitate the formation of a *COOH intermediate, as suggested by theoretical calculations. Consequently, CoTAP-iCONs exhibit higher CO₂ RR activity than other cobalt-porphyrin-based structures: an 870% and 480% improvement of CO current densities compared to the monomer and neutral nanosheets, respectively. Additionally, the iCONs structure can accommodate the cationic moieties. In a flow cell, CoTAP-iCONs attain a very small onset overpotential of 40 mV and a stable total current density of 212 mA cm^-2 with CO Faradaic efficiency of >95% at -0.6 V for 11 h. Further coupling the flow electrolyzer with commercial solar cells yields a solar-to-CO conversion efficiency of 13.89%. This work indicates that atom-thin, ionic nanosheets represent a promising structure for achieving both tailored activity and high stability.

Porphyrin-based conjugated organic polymer with dual metal sites for highly active and selective visible-light-driven reduction of CO2 to CO

A porphyrin-based conjugated organic polymer (COP) was constructed from 5,10,15,20-tetrakis(4-bromophenyl)porphyrin copper (CuTBPP) and 5,5'-bis-ethynyl-2,2'-bipyridine (BPY) via Sonogashira coupling. Its complex Co/CuTBPP-BPY-COP (with dual metal sites composed of copper porphyrin and a cobalt BPY unit) was prepared by coordination with Co²⁺. All of the prepared CuTBPP-BPY-COP and Co/CuTBPP-BPY-COP compounds exhibited excellent photocatalytic performance toward CO₂ reduction under visible-light irradiation without another sacrificial reagent but only H₂O. Co/CuTBPP-BPY-COP (dual metal sites) exhibited better photocatalytic activity than CuTBPP-BPY-COP (a single metal site). Co/CuTBPP-BPY-COP retained a higher photocatalysis capacity for CO₂ reduction after 10 consecutive cycles. The total quantity of CO product was 263.2 μmol g^-1 after 10 h of irradiation. Theoretical studies indicate that introducing Co metal centers and nitro groups are more favorable for the photoreduction catalysis of CO₂ compared with that using CuTBPP-BPY-COP.

Transition metal complexes with strong and long-lived excited state absorption: from molecular design to optical power limiting behavior

Transition metal complexes (TMCs) with strong and long-lived excited state absorption (ESA) usually exhibit high-performance optical power limiting (OPL) response. Several techniques, such as transmission vs. incident fluence curves and Z-scan have been widely used to assess the OPL performance of typical TMCs. The OPL performance of TMCs is highly molecular structure-dependent. Special emphasis is placed on the structure-OPL response relationships of Pt(II), Ir(III), Ru(II), and other metal complexes. This review concludes with perspectives on the current status of OPL field, as well as opportunities that lie just beyond its frontier.

Metalloporphyrin-Linked Mercurated Graphynes for Ultrastable CO2 Electroreduction to CO with Nearly 100% Selectivity at a Current Density of 1.2 A cm-2

The electrochemical reduction reaction of carbon dioxide (CO₂RR) to the desired feedstocks with a high faradaic efficiency (FE) and high stability at a high current density is of great importance but challenging owing to its poor electrochemical stability and competition with the hydrogen evolution reaction (HER). Guided by theoretical calculations, herein, a series of novel metalloporphyrin-linked mercurated graphynes (Hg-MTPP) were designed as electrocatalysts for CO₂RR, since the mercurated graphyne blocks induce a high HER overpotential. Notably, Hg-CoTPP was synthesized and produced a maximum CO FE of 95.6% at -0.76 V (vs reversible hydrogen electrode (RHE)) in an H-type cell, and a CO FE of 91.2% even at -1.26 V (vs RHE), due to a great suppression of HER. The Hg-CoTPP combined with N-doped graphene (Hg-CoTPP/NG) was able to achieve a high CO FE of nearly 100% at a current density of 1.2 A cm^-2 and particularly a ground-breaking stability of over 360 h at around 420 mA cm^-2 in a flow-type cell. Further experimental and computational results revealed that the mercurated graphyne of Hg-CoTPP brings a high HER overpotential and tunes the d-band electronic states of the metal center that make the d-band center closer to the Fermi level, thus enhancing the bonding of *COOH intermediates on Hg-CoTPP. The introduction of NG could shorten the Co-N coordination bonds, which enhances electron transfer to the metal center to lower the energy barrier for *COOH. Our results illustrated that Hg-MTPP could serve as a new class of two-dimensional (2D) materials and provide a design concept for developing efficient electrocatalysts for CO₂RR in commercial applications.

Metalated covalent organic frameworks: from synthetic strategies to diverse applications

Covalent organic frameworks (COFs) are a class of organic crystalline porous materials discovered in the early 21st century that have become an attractive class of emerging materials due to their high crystallinity, intrinsic porosity, structural regularity, diverse functionality, design flexibility, and outstanding stability. However, many chemical and physical properties strongly depend on the presence of metal ions in materials for advanced applications, but metal-free COFs do not have these properties and are therefore excluded from such applications. Metalated COFs formed by combining COFs with metal ions, while retaining the advantages of COFs, have additional intriguing properties and applications, and have attracted considerable attention over the past decade. This review presents all aspects of metalated COFs, from synthetic strategies to various applications, in the hope of promoting the continued development of this young field.

Effect of unwanted guest molecules on the stacking configuration of covalent organic frameworks: a periodic energy decomposition analysis

Elucidating the precise stacking configuration of a covalent organic framework, COF, is critical to fully understand their various applications. Unfortunately, most COFs form powder crystals whose atomic characterisations are possible only through powder X-ray diffraction (PXRD) analysis. However, this analysis has to be coupled with computational simulations, wherein computed PXRD patterns for different stacking configurations are compared with experimental patterns to predict the precise stacking configuration. This task is often computationally challenging firstly because, computation of these systems mostly rely on the use of semi-empirical methods that need to be adequately parametrised for the system being studied and secondly because some of these compounds possess guest molecules, which are not often taken into account during computation. COF-1 is an extreme case in which the presence of the guest molecule plays a critical role in predicting the precise stacking configuration. Using this as a case study, we mapped out a full PES for the stacking configuration in the guest free and guest containing system using the GFN-xTB semi-empirical method followed by a periodic energy decomposition analysis using first-principles Density Functional Theory (DFT). Our results showed that the presence of the guest molecule leads to multiple low energy stacking configurations with significantly different lateral offsets. Also, the semi-empirical method does not precisely predict DFT low energy configurations, however, it accurately accounts for dispersion. Finally, our quantum-mechanical analysis demonstrates that electrostatic-dispersion model suggested Hunter and Sanders accurately describes the stacking in 2D COFs as opposed to the newly suggested Pauli-dispersion model.

Chiral-Induced Ultrathin Covalent Organic Frameworks Nanosheets with Tunable Circularly Polarized Luminescence

Development of covalent organic frameworks (COFs) with circularly polarized luminescence (CPL) is still challenging. Here we first reported ultrathin COFs nanosheets (NS) based CPL materials using a chiral induced-synthesis strategy. Chiral amines served as chiral inducers to give COF TpBpy with chirality and participated in the modification of TpBpy, inhibiting the fluorescence quenching caused by π-π stacking to form ultrathin luminescent chiral COFs (chirCOFs) NS. The obtained chirCOFs R-/S-TpBpy NS had strong chirality and intense red CPL property with a |g_lum| of ∼0.02. Afterward, the carboxyl containing green and blue fluorescent dye molecules were postmodified onto the chirCOFs NS (chirCOFs/Dyes) to achieve color-adjustable CPL. Due to the chirality and energy transfer between chirCOFs and dye groups, the obtained chirCOFs/Dyes showed strong chirality and increased and tunable photoluminescence, exhibiting excellent, tunable, and amplified CPL performance with a maximum |g_lum| of ∼0.1, which was ∼5 times stronger than that of as-prepared chirCOFs NS. Moreover, the corresponding chirCOFs NS were dispersed into a polydimethylsiloxane (PDMS) matrix to form wafer size, highly transparent, and flexible COFs/PDMS films for practical CPL application. This study opens a new strategy to prepare ultrathin chirCOFs NS with strong and tunable CPL by chiral induction and provides a new approach for the preparation of transparent, large size, and flexible COFs composite films in chiral optical applications.

Construction of bifunctional electrochemical biosensors for the sensitive detection of the SARS-CoV-2 N-gene based on porphyrin porous organic polymers

In this study, a novel porphyrin-based porous organic polymer (POP) was constructed using 5,10,15,20-tetramine (4-aminophenyl) porphyrin (TAPP) and 5,5'-diformyl-2,2'-bipyridine (DPDD) as organic ligands via a solvothermal method (represented as TAPP-DPDD-POP). Then, it was utilized as a bifunctional scaffold for constructing a sensitive sensing strategy toward the nucleocapsid phosphoprotein (N-gene) of SARS-CoV-2. The obtained TAPP-DPDD-POP is composed of nanospheres with a size of 100-300 nm and possesses a highly conjugated and π-π stacking network. The coexistence of the porphyrin and bipyridine moieties of TAPP-DPDD-POP afforded considerable electrochemical activity and a strong binding interaction toward the SARS-CoV-2 N-gene-targeted antibody and targeted the aptamer strands of the N-gene. The TAPP-DPDD-POP-based aptasensor and immunosensor were manufactured for the sensitive analysis of SARS-CoV-2 N-gene, and exhibited the limit of detection (LOD) of 0.59 fg mL^-1 and 0.17 fg mL^-1, respectively, within the range of 0.1 fg mL^-1 to 1 ng mL^-1 of N-gene. The sensing performances of both the TAPP-DPDD-POP-based aptasensor and immunosensor were better than those of existing electrochemical biosensors for analyzing the N-gene, accompanied with excellent stability, high selectivity and reproducibility. The TAPP-DPDD-POP-based aptasensor and immunosensor were then employed to detect the N-gene from various environments, including human serum, river water, and seafoods. This work provides a new method of using an electrochemically active POP to sensitively and selectively analyze SARS-CoV-2 in diverse environments.

Tunable Third-Order Nonlinear Optical Effect via Modifying Ti4(embonate)6 Cage-Based Ionic Pairs

Benefiting from the strong inherent π-conjugation properties, the integration of Ti4L6 (L = embonate) cages and various N, N-chelated transition-metal cations into tightly packed structures accurately lead to the high-performance...

Oriented Assembly of 2D Metal-Pyridylporphyrinic Framework Films for Giant Nonlinear Optical Limiting

The development of metal-organic frameworks (MOFs) with nonlinear optical (NLO) properties is of pronounced significance for optical devices. Herein, a series of 2D MOFs ZnTPyP(M) (TPyP = 5,10,15,20-tetrakis(4-pyridyl)porphyrin, M = Cu, Ni, Mn, H₂) films with [010]-orientation growth composed of ultrathin nanosheets from a pyridylporphyrinic ligand are first obtained by using a liquid-phase epitaxial (LPE) layer-by-layer (lbl) growth approach. ZnTPyP(M) films show a giant nonlinear optical limiting (OL) response and can be modulated by tuning the type of metalloporphyrinic ligands. As a result, ZnTPyP(Cu) film exhibits the highest nonlinear absorption coefficient of 5.7 × 10^-6 m/W compared to other reported NLO materials. Density functional theory calculations were consistent with the experimental results, revealing that the tunable π-π* local excitation and the increased delocalization of the metalloporphyrinic group regulate the NLO performance of ZnTPyP(M) films. These findings provide new insight into the effect of 2D porphyrinic MOFs toward the NLO response and offer new film candidates for nonlinear OL application.

Controllable Synthesis and Performance Modulation of 2D Covalent-Organic Frameworks

Covalent-organic frameworks (COFs) are especially interesting and unique as their highly ordered topological structures entirely built from plentiful π-conjugated units through covalent bonds. Arranging tailorable organic building blocks into periodically reticular skeleton bestows predictable lattices and various properties upon COFs in respect of topology diagrams, pore size, properties of channel wall interfaces, etc. Indeed, these peculiar features in terms of crystallinity, conjugation degree, and topology diagrams fundamentally decide the applications of COFs including heterogeneous catalysis, energy conversion, proton conduction, light emission, and optoelectronic devices. Additionally, this research field has attracted widespread attention and is of importance with a major breakthrough in recent year. However, this research field is running with the lack of summaries about tailorable construction of 2D COFs for targeted functionalities. This review first covers some crucial polymeric strategies of preparing COFs, containing boron ester condensation, amine-aldehyde condensation, Knoevenagel condensation, trimerization reaction, Suzuki CC coupling reaction, and hybrid polycondensation. Subsequently, a summary is made of some representative building blocks, and then underlines how the electronic and molecular structures of building blocks can strongly influence the functional performance of COFs. Finally, conclusion and perspectives on 2D COFs for further study are proposed.

Interpenetrated Metal-Porphyrinic Framework for Enhanced Nonlinear Optical Limiting

Structural interpenetration in metal-organic frameworks (MOFs) significantly impacts on their properties and functionalities. However, understanding the interpenetration on third-order nonlinear optics (NLO) of MOFs have not been reported to date. Herein, we report two 3D porphyrinic MOFs, a 2-fold interpenetrated [Zn₂(TPyP)(AC)₂] (ZnTPyP-1) and a noninterpenetrated [Zn₃(TPyP)(H₂O)₂(C₂O₄)₂] (ZnTPyP-2), constructed from 5,10,15,20-tetra(4-pyridyl)porphyrin (TPyP(H₂)) and Zn(NO₃)₂ (AC = acetate, C₂O₄ = oxalate). ZnTPyP-1 achieves excellent optical limiting (OL) performance with a giant nonlinear absorption coefficient (3.61 × 10⁶ cm/GW) and large third-order susceptibility (7.73 × 10^-7 esu), which is much better than ZnTPyP-2 and other reported OL materials. The corresponding MOFs nanosheets are dispersed into a polydimethylsiloxane (PDMS) matrix to form highly transparent and flexible MOFs/PDMS glasses for practical OL application. In addition, the OL response optimized by adjusting the MOFs concentration in the PDMS matrix and the type of metalloporphyrin are discussed in the ZnTPyP-1 system. The theoretical calculation confirmed that the abundant π-π interaction from porphyrinic groups in the interpenetrated framework increased the electron delocalization/transfer and boosted the OL performance. This study opens a new avenue to enhance OL performance by the construction of interpenetrated structures and provides a new approach for the preparation of transparent and flexible MOF composites in nonlinear optical applications.

Editing Light Emission with Stable Crystalline Covalent Organic Frameworks via Wall Surface Perturbation

The ordered π skeletons of covalent organic frameworks make them viable light-emitting materials but their limited tunability has precluded further implementation. Here we report the synthesis of hydrazone-linked frameworks which are stable in water, acid, and base, and demonstrate their utility as a platform for light emission. The polygonal backbone is designed to be luminescent and partially π conjugated while the pore wall is docked with single atom or unit to induce resonance, hyperconjugation, and tautomerization effects. These effects can be transmitted to the backbone, so that the framework can emit three primary colors of light. The wall can be perturbated with multiple surface sites, rendering the material able to edit diverse emission colors in a predesignable and digital way. The systems show high activity, stability, tunability, and sensibility: a set of features attractive for light-emitting and sensing applications.

Ether-linked porphyrin covalent organic framework with broadband optical switch

It is still a challenge to design and synthesize novel switchable optical materials with ultrafast nonlinear optical (NLO) response in a broad spectral range. These materials have exhibited great application potential in many high-technology fields such as biological imaging, chemical sensors, optical data storage, laser protection, and controllable intelligent and optoelectronic devices. By using porphyrins with highly delocalized 18 π-electron conjugated system as functional building blocks, the first ether-linked porphyrin covalent organic framework materials (COF-Pors) with highly ordered lattice structure have been successfully synthesized. In contrast to the starting porphyrins that only exhibit reverse saturable absorption (RSA) response at 532 nm, the as-prepared COF-Pors shows large NLO effect in a broad range from visible to near infrared. Upon laser illumination, COF-Pors exhibits typical saturable absorption (SA) effect at lower incident laser energy, and RSA response at higher pulse energy.

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The first ether-linked porphyrin covalent organic framework (COF-Pors) was synthesized.

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COF-Pors exhibits reversible intensity-dependent SA to RSA transition in DMF dispersions.

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COF-Pors shows an NLO switching effect in a broad range from visible to near infrared.

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COF-Pors exhibits SA at lower pulse energy and RSA at higher pulse energy.

Crystalline Porous Materials for Nonlinear Optics

Crystalline porous materials have been extensively explored for wide applications in many fields including nonlinear optics (NLO) for frequency doubling, two-photon absorption/emission, optical limiting effect, photoelectric conversion, and biological imaging. The structural diversity and flexibility of the crystalline porous materials such as the metal-organic frameworks, covalent organic frameworks, and polyoxometalates provide numerous opportunities to orderly organize the dipolar chromophores and to systemically modify the type and concentration of these dipolar chromophores in the confined spaces, which are highly desirable for NLO. Here, the recent advances in the crystalline porous NLO materials are discussed. The second-order NLO of crystalline porous materials have been mainly devoted to the chiral and achiral structures, while the third-order NLO crystalline porous materials have been categorized into pure organic and hybrid organic/inorganic materials. Some representative properties and applications of these crystalline porous materials in the NLO regime are highlighted. The future perspective of challenges as well as the potential research directions of crystalline porous materials have been also proposed.

Conjugation-regulating synthesis of high photosensitizing activity porphyrin-based covalent organic frameworks for photodynamic inactivation of bacteria

Preparation of porphyrin-based covalent organic frameworks (Por-COFs) with high photosensitizing activity for photodynamic inactivation of bacteria is of great challenge, but significant for economy and human health. Herein, we show a conjugation-regulating strategy to design and synthesize Por-COFs with high photosensitizing activity for the photodynamic inactivation of bacteria. Terephthalaldehyde (Da), 2,5-Dihydroxyterephthalaldehyde (Dha), and 2,5-Diethoxyterephthalaldehyde (Deta) with different conjugation degrees are selected to condense with 5,10,15,20-Tetrakis(4-aminophenyl)porphyrin (Tph) to synthesize COF-366, DhaTph, and JNU-2, respectively. The higher conjugation of Dha and Deta than Da leads to the higher conjugation of DhaTph and JNU-2, respectively. Moreover, the hydroxyl group in Dha and the ethoxy group in Deta further expand the conjugation of DhaTph and JNU-2 via the formation of intralayer extended π-cloud delocalization and p-π conjunction, respectively. The extension of conjugation for DhaTph and JNU-2 results in the increase of intersystem crossing process and significantly improves their photosensitizing activity. Furthermore, JNU-2 with the highest photosensitizing activity exhibits superior antibacterial effects toward Staphylococcus aureus (99.1%) and Escherichia coli (96.8%). This study offers a new conjugation-regulating strategy for designing high photosensitizing activity of Por-COFs for the inactivation of bacteria.

An Ultrastable Crystalline Acylhydrazone-Linked Covalent Organic Framework for Efficient Removal of Organic Micropollutants from Water

As an important member of crystalline porous polymers, acylhydrazone-linked covalent organic frameworks (COFs) have gained much attention in recent years. However, the low structural stability imparts a limit on their practical applications. To tackle this problem, we report a simple strategy to increase the chemical stability of acylhydrazone-linked COFs by incorporating azobenzene groups in the conjugated framework. Through reinforcing the π-π stacking interactions between the adjacent layers with increased π-surface, it is surprising to find that the resulting materials exhibit extreme stability in harsh environments, such as in strong acid, strong base, aqueous educing agent and boiling water, even exposed to air for one year. As a proof-of-concept, such frameworks have been used to remove various organic micropollutants such as antibiotics, plastic components, endocrine disruptors, and carcinogens from water with high capacity, fast speed and excellent reusability over a wide pH range at environmentally relevant concentrations. The results provide a new avenue to significantly enhance the stability of COFs for practical applications.

Metallated Graphynes as a New Class of Photofunctional 2D Organometallic Nanosheets

Two-dimensional (2D) nanomaterials are attracting much attention due to their excellent electronic and optical properties. Here, we report the first experimental preparation of two free-standing mercurated graphyne nanosheets via the interface-assisted bottom-up method, which integrates both the advantages of metal center and graphyne. The continuous large-area nanosheets derived from the chemical growth show the layered molecular structural arrangement, controllable thickness and enhanced π-conjugation, which result in their stable and outstanding broadband nonlinear saturable absorption (SA) properties (at both 532 and 1064 nm). The passively Q-switched (PQS) performances of these two nanosheets as the saturable absorbers are comparable to or higher than those of the state-of-the-art 2D nanomaterials (such as graphene, black phosphorus, MoS₂ , γ-graphyne, etc.). Our results illustrate that the two metallated graphynes could act not only as a new class of 2D carbon-rich materials, but also as inexpensive and easily available optoelectronic materials for device fabrication.

Anionic Fluorinated Zn-porphyrin Combined with Cationic Endohedral Li-fullerene for Long-Lived Photoinduced Charge Separation with Low Energy Loss

Here we report an anionic meso-tetrakis(4-carboxymethylthio-2,3,5,6-tetrafluorophenyl) zinc porphyrin (ZnTF₄PPTC^4-) to form a supramolecular complex with a cationic lithium endohedral [60]fullerene (Li⁺@C₆₀). The supramolecular ZnTF₄PPTC^4-/Li⁺@C₆₀ complex formed by strong electrostatic attraction with a large binding constant generates a long-lived charge-separated (CS) state with low energy loss by photoinduced electron transfer from ZnTF₄PPTC^4- to Li⁺@C₆₀. The anionic fluorinated zinc porphyrin with high oxidation potential reduces the energy loss associated with the charge separation and enhances the energy level of the CS state. The energy level of the CS state determined by electrochemical measurements is at 0.94 eV, which is much higher than that of a similar supramolecular complex using an anionic meso-tetrakis(sulfonatophenyl) zinc porphyrin (ZnTPPS^4-) at 0.55 eV. Time-resolved transient absorption spectroscopy demonstrates that ZnTF₄PPTC^4-/Li⁺@C₆₀ generates a long-lived CS state with a lifetime of 0.29 ms in a binary solvent of acetonitrile and chlorobenzene. The lifetime of the CS state is comparable to that of ZnTPPS^4-/Li⁺@C₆₀ in benzonitrile.