Interpenetrated Metal-Porphyrinic Framework for Enhanced Nonlinear Optical Limiting

Controlling the Degree of Interpenetration in Chiral Three-Dimensional Covalent Organic Frameworks via Steric Tuning

Network interpenetration plays a crucial role in functionalizing porous framework materials. However, controlling the degree of interpenetration in covalent organic frameworks (COFs) to influence their pore sizes, shapes, and functionalities still remains a significant challenge. Here, we demonstrate a steric tuning strategy to control the degree of COF interpenetration and modulate their physicochemical properties. By imine condensations of 1,1'-bi-2-naphthol-derived tetraaldehydes bearing different alkyl substituents with the monomer tetra(p-aminophenyl)-methane, we synthesized and characterized a family of two-component and three-component chiral COFs with different interpenetrated dia networks. The alkyl groups are periodically appended on the pore walls, and their types/contents that can be synthetically tuned control the interpenetration degree of COFs by minimizing repulsive interactions between the alkyl groups. Specifically, the COF with -OH groups adopts an interpenetrated dia-c5 topology, those with -OMe/-OEt groups take an interpenetrated dia-c4 topology, whereas those with the bulky -OnPr/-OnBu groups exhibit a noninterpenetrated dia-c1 topology. The multivariate COFs with both -OH and -OnBu groups display either a noninterpenetrated or dia-c5 topology, depending on the proportion of -OnBu groups. The extent of interpenetration in COFs significantly affects their porosity, thermal stability, and chemical stability, resulting in varying selective performances in the adsorption and separation of dyes and asymmetric catalysis. This work highlights the potential of using steric hindrance to tune and control interpenetration, porosity, stability, and functionalities of COFs materials, broadening the range of their applications.

MOF-Derived Zn/N-Doped Porous Carbon Film on a Carbon Nanotube for High-Performance Supercapacitors

Designing high-performance binder-free electrochemical electrodes is crucially important toward supercapacitors. In this paper, a Zn/N-doped porous carbon film coating on flexible carbon nanotubes (ZIF-8@CT-800) derived from the epitaxial Zn-MOF film growth on cotton textile was successfully fabricated via a combination of the liquid-phase epitaxial (LPE) method and calcination treatments. The ZIF-8@CT-800 serves directly as a self-supported electrode for supercapacitors and exhibits a high areal capacitance of 930 mF·cm-2 at a current density of 1 mA·cm-2 and a good recyclability of 86% after 2000 cycles. The excellent supercapacitor property is ascribed to the unique structural design of ZIF-8@CT-800, which provides appropriate channels for enhanced electronic and ionic transport as well as increased surface area for accessing more electrolyte ions. This work will provide significant guidance for designing MOF-derived porous carbon to construct flexible binder-free electrode materials with high electrochemical performance.

Harvesting Multicolor Photoluminescence in Nonaromatic Interpenetrated Metal-Organic Framework Nanocrystals via Pressure-Modulated Carbonyls Aggregation

Interpenetrated metal-organic frameworks (MOFs) with nonaromatic ligands provide a unique platform for adsorption, catalysis, and sensing applications. However, nonemission and the lack of optical property tailoring make it challenging to fabricate smart responsive devices with nonaromatic interpenetrated MOFs based on ligand-centered emission. In this paper, the pressure-induced aggregation effect is introduced in nonaromatic interpenetrated Zn4O(ADC)4(Et3N)6 (IRMOF-0) nanocrystals (NCs), where carbonyl groups aggregation results in O─O distances smaller than the sum of the van der Waals radii (3.04 Å), triggering the photoluminescence turn-on behavior. It is noteworthy that the IRMOF-0 NCs display an ultrabroad emission tunability of 130 nm from deep blue (440 nm) to yellow (570 nm) upon release to ambient conditions at different pressures. The eventual retention of through-space n-π* interactions in different degrees via pressure treatment is primarily responsible for achieving a controllable multicolor emission behavior in initially nonemissive IRMOF-0 NCs. The fabricated multicolor phosphor-converted light-emitting diodes based on the pressure-treated IRMOF-0 NCs exhibit excellent thermal, chromaticity, and fatigue stability. The proposed strategy not only imparts new vitality to nonaromatic interpenetrated MOFs but also offers new perspectives for advancements in the field of multicolor displays and daylight illumination.

Intramolecular charge transfer enhanced optical limiting in novel hydrazone derivatives with a D1-D-Ai-π-A structure

The present paper investigates one of the hydrazone derivatives (BTH with a D-π-A structure) based on density functional theory. With the computation results of ground state absorption (GSA), excited-state absorption (ESA) and multi-photon absorption (MPA), the optical limiting effect observed in the experiment for the BTH molecule can be well predicted and elucidated by the MPA-ESA mechanism. The analysis of the hole-electron and the electron density differences between two transition states reveal that the main transitions involved in the GSA and ESA of BTH could be recognized as local excitation. Based on these observations, four novel hydrazone derivatives based on the BTH unit with a D1-D-Ai-π-A structure were designed to promote intramolecular charge transfer (ICT). It shows that the ICT effect is well improved by adding the D1 and Ai units. Compared with the original BTH molecule, the main bands of GSA and ESA of D1-D-Ai-π-A molecules are both red-shifted. In addition, GSA, ESA and MPA probabilities are all improved because the obvious charge transfer character results in the transition dipole moment change from localized to delocalized. Accordingly, the optical limiting effect in these hydrazone derivatives is well enhanced. These observations provide guidance for designing novel optical limiting materials based on the hydrazone derivatives.

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.

Electro-Induced Phase Transformation of a Conductive Metal-Organic Framework Film for Nonlinear Optical Switching

Achieving metal-organic frameworks (MOFs) with nonlinear optical (NLO) switching is profoundly important. Herein, the conductive MOFs Cu-TCNQ phase I (Ph-I) and phase II (Ph-II) films were prepared using the liquid-phase-epitaxial layer-by-layer spin-coating method and steam heating method, respectively. Electronic experiments showed that the Ph-II film could be changed into the Ph-I film under an applied electric field. The third-order NLO results revealed that the Ph-I film had a third-order nonlinear reverse saturation absorption (RSA) response and the Ph-II film displayed a third-order nonlinear saturation absorption (SA) response. With increases in the heating time and applied voltage, the third-order NLO response realized the reversible transition between SA and RSA. The theoretical calculations indicated that Ph-I possessed more interlayer charge transfer, resulting in a third-order nonlinear RSA response that was stronger than that of Ph-II. This work applies phase-transformed MOFs to third-order NLO switching and provides new insights into the nonlinear photoelectric applications of MOFs.

Third-Order Nonlinear Optical Modulation Behavior of Photoresponsive Bimetallic MOFs

Bimetallic metal-organic frameworks (MOFs) capable of sensing external stimuli will provide more possibilities for further regulating third-order nonlinear optical (NLO) properties. In this work, we synthesized bimetallic MOFs (ZnCu-MOF and ZnCd-MOF) through central metal exchange using a photoresponsive Zn-MOF as a precursor. Compared with Zn-MOF, both ZnCu-MOF and ZnCd-MOF exhibit significantly enhanced third-order NLO absorption properties. This is mainly attributed to the introduction of metal ions with different electron configurations that can adjust the bandgap of MOFs and enhance electron delocalization, thus promoting electron transfer. Interestingly, the bimetallic MOFs show a transition from reverse saturation absorption (RSA) to saturation absorption (SA) after exposure to ultraviolet irradiation, as they retain the properties of directional photogenerated electron transfer. Photoresponsive bimetallic MOFs not only have the effect of bimetallic modulation of electronic structures but also have the characteristics of photoinduced electron transfer, exhibiting diversified optical properties. These findings provide a novel method for the development of multifunctional NLO materials.

Assembly of Homochiral Aluminum Oxo Clusters for Circularly Polarized Luminescence

Chiral aluminum oxo clusters (cAlOCs) are distinguished from other classes of materials on account of their abundance in the earth's crust and their potential for sustainable development. However, the practical synthesis of cAlOCs is rarely known. Herein, we adopt a synergistic coordination strategy by using chiral amino acid ligands as bridges and auxiliary pyridine-2,6-dicarboxylic acid as chelating ligands and successfully isolate an extensive family of cAlOCs. They integrate molecular chirality, absolute helicity, and intrinsic hydrogen-bonded chiral topology. Moreover, they have the structural characteristics of one-dimensional channels and replaceable counteranions, which make them well combined with fluorescent dyes for circularly polarized luminescence (CPL). The absolute luminescence dissymmetry factor (glum) of up to the 10-3 order is comparable to several noble metals, revealing the enormous potential of cAlOCs in low-cost chiral materials. We hope this work will inspire new discoveries in the field of chirality and provide new opportunities for constructing low-cost chiral materials.

Meltable Aluminum Molecular Rings with Fluorescence and Nonlinear Optical Properties

Crystal-liquid-glass, which combines the tunable properties of crystalline compounds with the processability of glasses, has emerged as a new class of materials for fabricating bulk-shapable devices in real applications. Inspired by the characteristics of deep eutectic solvent (DES) mixtures involving significant depressions in melting points compared to their neat constituent components, in this study, we designed and synthesized the first examples of meltable aluminum oxo clusters (AlOCs) via lattice doping with DESs at the molecular level. The abundant and strong hydrogen bonding between the aluminum molecular ring, DES components, and lattice solvents is postulated to be the root that affords melting point depressions and, thus, "melting" clusters. We prepared a transparent bubble-free glass film under autogenous pressure using a hot-press method. These cluster-based films exhibited luminescent and nonlinear optical properties similar to those of pristine crystalline compounds. Our study belongs to the interdisciplinary disciplines of chemistry and physics. It not only breaks the limitations of crystalline glass on metal and ligand types but also acts as a general guide for extending the range of meltable crystalline materials.

Ferric Oxide Nanocrystals-Embedded Co/Fe-MOF with Self-Tuned d-Band Centers for Boosting Urea-Assisted Overall Water Splitting

A novel semiconductive Co/Fe-MOF embedded with Fe2 O3 nanocrystals (Fe2 O3 @CoFe-MOF) is developed as a trifunctional electrocatalyst for the urea oxidation reaction (UOR), oxygen evolution reaction (OER), and hydrogen evolution reaction for enhancing the efficiency of the hydrogen production via the urea-assisted overall water splitting. Fe2 O3 @CoFe-TPyP-MOF comprises unsaturated metal-nitrogen coordination sites, affording enriched defects, self-tuned d-band centers, and efficient π-π interaction between different layers. Density functional theory calculation confirms that the adsorption of urea can be optimized at Fe2 O3 @CoFe-TPyP-MOF, realizing the efficient adsorption of intermediates and desorption of the final product of CO2 and N2 characterized by the in situ Fourier transform infrared spectroscopy. The two-electrode urea-assisted water splitting device-assembled with Fe2 O3 @CoFe-TPyP-MOF illustrates a low cell voltage of 1.41 V versus the reversible hydrogen electrode at the current density of 10 mA cm-2 , attaining the hydrogen production rate of 13.13 µmol min-1 in 1 m KOH with 0.33 m urea. The in situ electrochemical Raman spectra and other basic characterizations of the used electrocatalyst uncover that Fe2 O3 @CoFe-TPyP-MOF undergoes the reversible structural reconstruction after the UOR test, while it demonstrates the irreversible reconstruction after the OER measurement. This work redounds the progress of urea-assisted water spitting for hydrogen production.

Structure and optical limiting effects of heterometallic Ag6@Ti12 and Ag8@Ti12 oxo clusters regulated by alkynyl ligands

Heterometallic Ag6@Ti12 and Ag8@Ti12 oxo clusters were prepared through a strategy of protecting polynuclear silver cores by a hollow Ti-O module. The introduction of alkyne ligands has shown significant influence on their structures and optical limiting effects.

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.

Two pairs of chiral YbIII enantiomers presenting distinct NIR luminescence and circularly polarized luminescence performances with giant differences in second-harmonic generation responses

By introducing enantiomerically pure mono-bidentate N-donor ligands (LR/LS) into Yb(btfa)3(H2O)2 and Yb(dbm)3(H2O), respectively, two pairs of chiral YbIII enantiomers, namely Yb(btfa)3LR/Yb(btfa)3LS (D-1/L-1) and [Yb(dbm)3LR]·[Yb(dbm)3(C2H5OH)]/[Yb(dbm)3LS]·[Yb(dbm)3(C2H5OH)] (D-2/L-2) were isolated, where btfa- = 3-benzoyl-1,1,1-trifluoroacetonate, dbm- = dibenzoylmethanate, and LR/LS = (-)/(+)-4,5-pinenepyridyl-2-pyrazine. D-1/L-1 possess mononuclear structures in which the YbIII ions are eight-coordinated, while D-2/L-2 show cocrystal structures containing Yb(dbm)3(LR/LS) and Yb(dbm)3(C2H5OH) moieties in which the two YbIII ions are eight and seven-coordinated, respectively. They not only feature different molecular structures but also present distinct linear and nonlinear optical performances. Chiral mononuclear D-1 has better near infrared photo-luminescence (NIR-PL) and circularly polarized luminescence (CPL) performances than chiral cocrystal D-2. More remarkably, D-1/L-1 show large second-harmonic generation (SHG) responses (up to 1.25/1.28 × KDP) 18/16 times those of D-2/L-2 (0.07/0.08 × KDP). In addition, D-2/L-2 represent the first examples of lanthanide cocrystal complexes with NIR-PL, NIR-CPL and SHG properties.

Towards high-performance nonlinear optical materials through embedding a D-A system into β-ketoenamine-linked COFs

Two covalent organic framework (COF) films supported by a glass substrate were obtained by solvothermal reaction of an electron donor with electron acceptor 1,3,5-triformylbenzene (TF) or 2,4,6-triformylphloroglucinol (TFP), respectively. The TFP-BD film exhibits a nonlinear absorption coefficient of -3.01 × 105 cm GW-1. The TFP-BD film can aggregate electrons around the connected monomer through the D-A effect due to its highly polar and electronegative carbonyl oxygen atoms, thereby modulating the electronic structure of the COFs. This work provides a novel approach for the structural modulation of optical materials with strong nonlinearity.

Superoleophilic conjugated microporous polymer nano-surfactants for realizing unprecedented fast recovery of volatile organic compounds

A pervaporation membrane with fast and selective permeation is key to improving the recovery efficiency of volatile organic compounds from water. Here, we synthesize a new type of nanofiller-conjugated microporous polymer (CMP) to fabricate polydimethylsiloxane (PDMS)-based mixed matrix membranes (MMMs) and explore their application in the recovery of organic solvents from water via pervaporation. Due to their good dispersibility in the dope solvent and compatibility with PDMS, uniform MMMs without discrete particle phases or aggregates are prepared. Interestingly, CMP nanosheets play a unique role as a nano-surfactant in enhancing both the sorption and diffusion coefficients, realizing unprecedented fast recovery of organic solvents from water. The total flux of the as-fabricated membranes can be enhanced from 74.8 to 406.2 kg μm-2 h-1 and the separation factor αethyl acetate/water is increased from 118.7 to 526.6 when using 5 wt% ethyl acetate aqueous solution as the feed at 50 °C. In addition, the CMP-incorporated PDMS membranes are also effective in recovering a wide range of organic compounds from water, including ethanol, acetone, tetrahydrofuran and acetonitrile.

Why Ligand Doping Increases the Fluorescence of an Anthracene-Based Metal-Organic Framework

Metal-organic frameworks (MOFs) built from fluorescent ligands frequently exhibit enhanced fluorescence when doped with inert ligands. This study focuses on a MOF of the UiO-68 structure, which is built from a fluorescent dibenzoate-anthracene ligand doped with a dibenzoate-benzene ligand. Our investigation aims to understand the mechanism behind the doping-enhanced emission of this MOF. We rule out several possible mechanisms, including exciton coupling, electron transfer between ligand and metal center, and ligand intersystem crossing induced by the metal center. Inhibition of the interligand charge transfer is considered a possible way to enhance emission. Furthermore, we propose that the conformational change of the anthracene-based ligand in the MOF cavity is also a way for enhancement. Our molecular dynamics simulations of the MOF structure filled with solvents reveal that the steric crowding in the cavity induces a conformational change at different doping levels, affecting the rate of intersystem crossing of the ligand.

Coordination-Induced Symmetry Breaking on Metal-Porphyrinic Framework Thin Films for Enhanced Nonlinear Optical Limiting

Structural asymmetry affecting the nonlinear optics (NLO) of metal-organic frameworks (MOFs) is very important in fundamentals and applications but is still a challenge. Herein we develop a series of indium-porphyrinic framework (InTCPP) thin films and provide the first study on the coordination-induced symmetry breaking on their third-order NLO. The continuous and oriented InTCPP(H₂) thin films were grown on quartz substrates and then postcoordinated with different cations (Fe²⁺ or Fe³⁺Cl^-) in InTCPP(H₂) (named InTCPP(Fe²⁺) and InTCPP(Fe³⁺Cl^-)). The third-order NLO results reveal the Fe²⁺ and Fe³⁺Cl^- coordinated InTCPP thin films have substantially enhanced NLO performance. Moreover, InTCPP(Fe³⁺Cl^-) thin films cause symmetry breaking of microstructures, resulting in a 3-fold increase in the nonlinear absorption coefficient (up to 6.35 × 10^-6 m/W) compared to InTCPP(Fe²⁺). This work not only develops a series of nonlinear optical MOF thin films but also provides new insight into symmetry breaking on MOFs for nonlinear optoelectronic applications.

Recyclable TPA-Modified MIL-88-Supported Ionic Pt as a Highly Efficient Catalyst for Alkene Hydrosilylation

The hydrosilylation reaction driven by a homogeneous catalyst has been widely used in the industrial synthesis of functionalized silicone compounds. However, the homogeneous catalyst for hydrosilylation has the shortcomings of nonrecyclability, undesirable side reactions, and high cost. In this work, a highly efficient heterogeneous catalyst was prepared by loading Pt ions on MIL-88 modified with trimethoxy[3-(phenylamino)propyl]silane. In comparison with previous research studies, the resulting catalyst can exhibit high catalytic activity and excellent stability during the hydrosilylation reaction, which was attributed to the presence of a pyrrolic nitrogen structure between TPA-MIL-88 and the Pt ion. Besides them, 1.2%Pt/TPA-MIL-88 showed the highest catalytic activity and can be reused five times without significant deactivation. Importantly, 1.2%Pt/TPA-MIL-88 also achieved satisfactory results when it was used to catalyze the hydrosilylation reaction for other olefins, implying great potential for application in the silicone industry.

Ultrafast optical limiting ability of trans-stilbene enhanced and broadened by a donor-π-acceptor structure

It has been shown that trans-stilbene (TSB) has great potential as an ultrafast optical limiting material through the process of three-photon absorption (3PA)-induced excited state absorption (ESA). The present paper shows that the main transitions in the absorption bands of TSB are mostly local excitation. In order to improve the optical limiting performance of TSB, a series of TSB derivatives with an electron donor-π-acceptor structure are designed. The analysis of π electron localized orbital locators (LOL-π) reveals that the distribution of π electrons in the derivatives of TSB is much more continuous compared to that in the original TSB. This results in the main transitions in the ground state absorption (GSA) and ESA of the TSB derivatives showing obvious charge transfer characteristics, and the GSA, ESA and 3PA bands are largely enhanced and broadened compared to those of the original TSB molecule. These observations are well supported by the enlarged transition dipole moments of the main transitions in GSA and ESA. With these results, it is clearly shown that the TSB derivatives are promising optical limiting materials. Our observations provide clues for the development of optical limiting materials based on TSB.

Dislocated Bilayer MOF Enables High-Selectivity Photocatalytic Reduction of CO2 to CO

The highly selective photoreduction of CO₂ into valuable small-molecule chemical feedstocks such as CO is an effective strategy for addressing the energy crisis and environmental problems. However, it remains a challenge because the complex CO₂ photoreduction process usually generates multiple possible products and requires a subsequent separation step. In this paper, 2D monolayer and bilayer porphyrin-based metal-organic frameworks (MOFs) are successfully constructed by adjusting the reaction temperature and solvent polarity with 5,10,15,20-tetrakis(4-pyridyl)porphyrin as the light-harvesting ligand. The bilayer MOF is a low-dimensional MOF with a special structure in which the upper and lower layers are arranged in dislocation and are bridged by halogen ions. This bilayer MOF exhibits 100% ultra-high selectivity for the reduction of CO₂ to CO under simulated sunlight without any cocatalyst or photosensitizer and can be recycled at least three times. The intrinsic mechanism of this photocatalytic CO₂ reduction process is explored through experimental characterization and density functional theory (DFT) calculations. This work shows that the rational design of the number of layers in 2D MOF structures can tune the stability of these structures and opens a new avenue for the design of highly selective MOF photocatalysts.

Enhancing Third-Order Nonlinear Optical Property by Regulating Interaction between Zr4(embonate)6 Cage and N, N-Chelated Transition-Metal Cation

Herein, the combination of anionic Zr₄L₆ (L = embonate) cages and N, N-chelated transition-metal cations leads to a series of new cage-based architectures, including ion pair structures (PTC-355 and PTC-356), dimer (PTC-357), and 3D frameworks (PTC-358 and PTC-359). Structural analyses show that PTC-358 exhibits a 2-fold interpenetrating framework with a 3,4-connected topology, and PTC-359 shows a 2-fold interpenetrating framework with a 4-connected dia network. Both PTC-358 and PTC-359 can be stable in air and other common solvents at room temperature. The investigations of third-order nonlinear optical (NLO) properties indicate that these materials show different degrees of optical limiting effects. It is surprising that increasing coordination interactions between anion and cation moieties can effectively enhance their third-order NLO properties, which can be attributed to the formation of coordination bonds that facilitate charge transfer. In addition, the phase purity, UV-vis spectra, and photocurrent properties of these materials were also studied. This work provides new ideas for the construction of third-order NLO materials.

Fine-Tuning Tridentate Ligands for the Construction of Nanotube-Based Boron Imidazolate Frameworks with High Chemical Stability

Two unusual nanotube-based boron imidazolate frameworks (BIF-134 and BIF-135) were synthesized by a dual-ligand synthetic strategy under solvothermal conditions. In the structure of BIF-134 ([Co(BH(2-mim)₃)(BTC)_1/3](HBH(2-mim)₃)_1/3(NMA); 2-mim = 2-methylimidazole, NMA = N-methylacetamide, and BTC = 1,3,5-benzene tricarboxylate), one part of boron imidazolate ligands participate in the structural skeleton coordination, while another part of boron imidazolate ligands act as guest molecules that are located between adjacent nanotubes, which enhance the stability of the framework by the host-guest interaction and the pore space partition effects. It was found to be highly stable in air, water, organic solvents, and a wide pH range (pH 0-12). However, in the structure of BIF-135 ([Zn(BH(2-mim)₃)(CHTC)_1/3]; CHTC = 1,3,5-cyclohexanetricarboxylate), all boron imidazolate ligands participate in the structural skeleton coordination; there is no boron imidazolate guest molecule in the pores. The topology of BIF-135 is similar to that of BIF-134 by replacing BTC with CHTC and replacing Co with Zn. Furthermore, the obtained BIFs exhibited third-order nonlinear optical properties and potential optical limiting applications demonstrated by reverse saturable absorption.

Postsynthetic Modification of NU-1000 for Designing a Polyoxometalate-Containing Nanocomposite with Enhanced Third-Order Nonlinear Optical Performance

For the advancement of laser technologies and optical engineering, various types of new inorganic and organic materials are emerging. Metal-organic frameworks (MOFs) reveal a promising use in nonlinear optics, given the presence of organic linkers, metal cluster nodes, and possible delocalization of π-electron systems. These properties can be further enhanced by the inclusion of solely inorganic materials such as polyoxometalates as prospective low-cost electron-acceptor species. In this study, a novel hybrid nanocomposite, namely, SiW₁₂@NU-1000 composed of SiW₁₂ (H₄SiW₁₂O₄₀) and Zr-based MOF (NU-1000), was assembled, completely characterized, and thoroughly investigated in terms of its nonlinear optical (NLO) performance. The third-order NLO behavior of the developed system was assessed by Z-scan measurements using a 532 nm laser. The effect of two-photon absorption and self-focusing was significant in both NU-1000 and SiW₁₂@NU-1000. Experimental studies suggested a much superior NLO performance of SiW₁₂@NU-1000 if compared to that of NU-1000, which can be assigned to the charge-energy transfer between SiW₁₂ and NU-1000. Negligible light scattering, good stability, and facile postsynthetic fabrication method can promote the applicability of the SiW₁₂@NU-1000 nanocomposite for various optoelectronic purposes. This research may thus open new horizons to improve and enhance the NLO performance of MOF-based materials through π-electron delocalization and compositing metal-organic networks with inorganic molecules as electron acceptors, paving the way for the generation of novel types of hybrid materials for prospective NLO applications.

Electrically regulating nonlinear optical limiting of metal-organic framework film

Regulating nonlinear optical (NLO) property of metal−organic frameworks (MOFs) is of pronounced significance for their scientific research and practical application, but the regulation through external stimuli is still a challenging task. Here we prepare and electrically control the nonlinear optical regulation of conductive MOFs Cu-HHTP films with [001]- (Cu-HHTP_[001]) and [100]-orientations (Cu-HHTP_[100]). Z-scan results show that the nonlinear absorption coefficient (β) of Cu-HHTP_[001] film (7.60 × 10⁻⁶ m/W) is much higher than that of Cu-HHTP_[100] film (0.84 × 10⁻⁶ m/W) at 0 V and the β of Cu-HHTP_[001] and Cu-HHTP_[100] films gradually increase to 3.84 × 10⁻⁵ and 1.71 × 10⁻⁶ m/W at 10 V by increasing the applied voltage, respectively. Due to 2D Cu-HHTP having anisotropy of charge transfer in different orientations, the NLO of MOFs film can be dependent on their growth orientations and improved by tuning the electrical field. This study provides more avenues for the regulation and NLO applications of MOFs.

Nonlinear optical properties of metal-organic framework can be tuned for potential optical applications. Here the authors demonstrate an enhancement the nonlinear absorption coefficient of MOF film by applying external electric field.

Surface, Interface and Structure Optimization of Metal-Organic Frameworks: Towards Efficient Resourceful Conversion of Industrial Waste Gases

Industrial waste gas emissions from fossil fuel over-exploitation have aroused great attention in modern society. Recently, metal-organic frameworks (MOFs) have been developed in the capture and catalytic conversion of industrial exhaust gases such as SO₂ , H₂ S, NO_x , CO₂ , CO, etc. Based on these resourceful conversion applications, in this review, we summarize the crucial role of the surface, interface, and structure optimization of MOFs for performance enhancement. The main points include (1) adsorption enhancement of target molecules by surface functional modification, (2) promotion of catalytic reaction kinetics through enhanced coupling in interfaces, and (3) adaptive matching of guest molecules by structural and pore size modulation. We expect that this review will provide valuable references and illumination for the design and development of MOF and related materials with excellent exhaust gas treatment performance.

Complete Inhibition of the Rotation in a Barrierless TICT Probe for Fluorescence-On Qualitative Analysis

Inhibition of twisting intramolecular charge transfer (TICT) is one of the most attractive methods for fluorescence-on analysis, whereas it remains enigmatic whether the fluorescence in a TICT-based probe could be thoroughly lightened. Here, for maximizing the fluorescence-on signal of the TICT-based probe, we develop a model by employing chemical reaction to directly cleave the linkage between the rotational electron donor and acceptor with a predisposed fluorescent signal close to zero. To validate this assumption, a nonfluorescent probe with barrierless rotation is successfully achieved by grafting acryloyl with -C═C- recognition sites onto coumarin, and 7-hydroxycoumarin with bright blue fluorescence could be released within 3 s upon probing KMnO₄ with an amount as low as 0.95 nM and 6.6 pg. We believe that the present strategy could not only deepen the insights of photochemistry but also facilitate the development of a theranostic drug delivery system, energy conversion, pollution control, and health risk reduction.

Optimizing Photodetectors in Two-Dimensional Metal-Metalloporphyrinic Framework Thin Films

Two-dimensional (2D) metalloporphyrin-based MOF thin films possessing abundant π-π interactions are promising materials for photoelectronic devices, but no reports on fabrication of photodetectors are available so far. Herein, a series of 2D MOF Zn2[TCPP(M)] (named ZnTCPP(M); TCPP = 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin; M = Zn, Mn, Fe, and H2) films with [001] orientation are fabricated on SiO2/Si substrates by the liquid-phase epitaxial (LPE) layer-by-layer (lbl) approach and further assembled to photodetectors. The obtained ZnTCPP(M)-based photodetectors exhibit an excellent photoresponse due to abundant π-π stacking between the MOF layers. Moreover, the metalloporphyrinic groups in ZnTCPP(M) have a significant influence on modulating the photoresponse of the photodetectors, among which the prepared ZnTCPP(Zn) film-based device exhibits the best photodetection performance with a high on/off ratio of 2.3 × 104, responsivity (Rλ, up to 10.3 A W-1), short rise/fall times (0.09/0.07 s), and a large detectivity (D*) of 8.1 × 1013 Jones. Density functional theory (DFT) calculations reveal that the perturbation of the ring π-electron system and the introduction of low-lying states as well as the large delocalization of the metalloporphyrinic group will adjust the photodetection performance of ZnTCPP(M) films. These results will provide a new understanding of the modulation of 2D metalloporphyrinic MOFs toward photodetection performance and perspective for the fabrication of photoelectronic devices.

Induction of Chirality in Boron Imidazolate Frameworks: The Structure-Directing Effects of Substituents

By enhancing steric hindrance of substituents on the imidazole ring, the fan-shaped molecule of a tridentate boron imidazolate ligand (KBH(2-ipim)₃, 2-ipim = 2-isopropylimidazolate) with racemic chirality was obtained. Then, seven novel boron imidazolate frameworks (BIFs) were prepared by mixing KBH(2-ipim)₃ ligands with various derivatives of benzene carboxylic acid under solvothermal conditions. All of these seven materials contain a ladder-like zinc-boron-imidazolate chain as a basic building block, and the ligand BH(2-ipim)₃^- exists in the same handedness in one chain. The structural variations are associated with the position of substituents of the auxiliary ligand. Of particular interest is the spontaneous resolution of BH(2-ipim)₃^- ligands into two independent enantiomorphous homochiral structures, BIF-131-S and BIF-131-R, which contain both a chiral chain and an absolute helix embedded in the nets.

Two-dimensional metal-organic frameworks: from synthesis to bioapplications

As a typical class of crystalline porous materials, metal-organic framework possesses unique features including versatile functionality, structural and compositional tunability. After being reduced to two-dimension, ultrathin metal-organic framework layers possess more external excellent properties favoring various technological applications. In this review article, the unique structural properties of the ultrathin metal-organic framework nanosheets benefiting from the planar topography were highlighted, involving light transmittance, and electrical conductivity. Moreover, the design strategy and versatile fabrication methodology were summarized covering discussions on their applicability and accessibility, especially for porphyritic metal-organic framework nanosheet. The current achievements in the bioapplications of two-dimensional metal-organic frameworks were presented comprising biocatalysis, biosensor, and theranostic, with an emphasis on reactive oxygen species-based nanomedicine for oncology treatment. Furthermore, current challenges confronting the utilization of two-dimensional metal-organic frameworks and future opportunities in emerging research frontiers were presented.

Black Titanium-Oxo Clusters with Ultralow Band Gaps and Enhanced Nonlinear Optical Performance

A series of catecholate-functionalized titanium-oxo clusters (TOCs), PTC-271 to PTC-277, with atomically precise structures were synthesized and characterized, including distinctive "boat" and "chair" conformations in PTC-273 and PTC-274, respectively. These cluster compounds are prominent for their ultralow optical band gaps, as is visually evident from the rather unusual black TOCs (B-TOCs), PTC-272 to PTC-277. The cluster structures were found to be ultrastable with respect to air, water, organic solvents, and even acidic or basic aqueous solutions in a wide pH range (pH 0-13), owing to the stabilizing effects of catecholate and its derivatives, as well as the carboxylate ligands. Another prominent feature is the occurrence of third-order nonlinear optical (NLO) performance, which has previously been unreported in the field of homometallic titanium-oxo clusters. Open-aperture Z-scan experiments show significant solid-state optical limiting (OL) applications of these B-TOCs, with high laser irradiation stability and low minimum normalized transmittance (T_min) of PTC-273 as ∼0.17. Meanwhile, theoretical calculations indicate that the smaller band gaps of B-TOCs were beneficial for strengthening the NLO response. This work not only represents a significant milestone in the construction of stable low-band gap black titanium oxide materials but also contributes to the mechanism insights into their optical applications.

Record Aluminum Molecular Rings for Optical Limiting and Nonlinear Optics

Crystalline cluster materials, a class of functional motif aggregations, provide a great opportunity for tuning the properties stemming from the flexible and accurate variation of inorganic and organic compositions. In this study, we demonstrate the effects of functional ligand and ring size regulation on the structures and third-order nonlinear optical (NLO) properties. Revealed by the single-crystal X-ray analysis results, aluminum molecular ring expansion is achieved by 2×9 and 3×6 strategies. In terms of the given organic shells, we further tuned the aluminum molecular ring sizes from 3.0 nm to 1.7 nm. The picosecond Z-scan measurements results revealed that the third-order NLO performances do not only depend on the general conjugate interactions but are also related to hydrogen bonding, polarizability, and ring sizes. The large nonlinear absorption coefficient and onset prove that the observed samples are promising candidates for the field of nonlinear optics.

Three-Photon-Induced Singlet Excited-State Absorption for the Tunable Ultrafast Optical-Limiting in Distyrylbenzene: A First-Principles Study

The ground and first singlet excited state absorption in distyrylbenzene(DSB) are simulated based on the linear-response time dependent density functional theory(LR-TDDFT). It is found that distyrylbenzene shows strong reverse saturable...

Enhanced nonlinear optical properties of a π-conjugated porphyrin dimer–graphene nanocomposite

A more conjugated nanocomposite and a potential NLO candidate with a strong intrasystem interaction were constructed using a rarely mentioned porphyrin dimer and graphene.

Novel Third-Order Nonlinear Optical Materials with Craig-Möbius Aromaticity

Electron delocalization in aromatic materials significantly impacts their third-order nonlinear optics (NLO). Despite organometallic complexes with Craig-Möbius aromaticity attracting great attention for their unusual physicochemical properties, their third-order NLO have been little studied to date. Herein, 12 Craig-Möbius aromatic organometallics with a stable structure similar to osmapentalyne, namely, carbolong complexes, are screened by DFT. They exhibit high third-order NLO responses because of the d and p electron delocalization in the organometallic ring. Furthermore, electron-hole distribution analyses draw a conclusion that extending the conjugated plane will increase the π-conjugation system to enhance the local excitation in the plane, and the introduction of typical aromatic ligands can result in the organometallic ring-to-ligand charge transfer (RLCT), which are effective methods to improve the third-order NLO response. This study opens a new window in the application of Craig-Möbius aromatic complexes and provides a new approach for third-order NLO materials design.