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.

Isolated Ni Atoms Enable Near-Unity CH4 Selectivity for Photothermal CO2 Hydrogenation.

Photothermal hydrogenation of carbon dioxide (CO2) into value-added products is an ideal solution for addressing the energy crisis and mitigating CO2 emissions. However, achieving high product selectivity remains challenging due to the simultaneous occurrence of numerous competing intermediate reactions during CO2 hydrogenation. We present a novel approach featuring isolated single-atom nickel (Ni) anchored onto indium oxide (In2O3) nanocrystals, serving as an effective photothermal catalyst for CO2 hydrogenation into methane (CH4) with a remarkable near-unity (∼99%) selectivity. Experiments and theoretical simulations have confirmed that isolated Ni sites on the In2O3 surface can effectively stabilize the intermediate products of the CO2 hydrogenation reaction and reduce the transition state energy barrier, thereby changing the reaction path to achieve ultrahigh selective methanation. This study provides comprehensive insights into the design of single-atom catalysts for the highly selective photothermal catalytic hydrogenation of CO2 to methane.

Aluminum Molecular Ring Meets Deep Eutectic Solvents: Adaptive Assembly and Optical Behavior.

Different from the previous neutral reaction solvent system, this work explores the synthesis of Al-oxo rings in ionic environments. Deep eutectic solvents (DESs) formed by quaternary ammonium salts hydrogen bond acceptor (HBA) and phenols hydrogen bond donor (HBD) further reduce the melting point of the reaction system and provide an ionic environment. Further, the quaternary ammonium salt was chosen as the HBA because it contains a halogen anion that matches the size of the central cavity of the molecular ring. Based on this thought, five Al8 ion pair cocrystals were synthesized via "DES thermal". The general formula is Q+ ⊂ {Cl@[Al8(BD)8(µ2-OH)4L12]} (AlOC-180-AlOC-185, Q+ = tetrabutylammonium, tetrapropylammonium, 1-butyl-3-methylimidazole; HBD = phenol, p-chlorophenol, p-fluorophenol; HL = benzoic acid, 1-naphthoic acid, 1-pyrenecarboxylic acid, anthracene-9-carboxylic acid). Structural studies reveal that the phenol-coordinated Al molecular ring and the quaternary ammonium ion pair form the cocrystal compounds. The halogen anions in the DES component are confined in the center of the molecular ring, and the quaternary ammonium cations are located in the organic shell. Such an adaptive cocrystal binding pattern is particularly evident in the structures coordinated with low-symmetry ligands such as naphthoic acid and pyrene acid. Finally, the optical behavior of these cocrystal compounds is understood from the analysis of crystal structure and theoretical calculation.

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.

Integrated Anionic Zirconium-Organic Cage and Cationic Boron-Imidazolate Cage for Synergetic Optical Limiting.

Making oppositely charged metal-organic cages (MOCs) into a tightly ordered structure may bring interesting functions. Herein, we report a novel structure composed of anionic (Zr4 L6 )8- (L=embonate) tetrahedral cages and in situ-formed cationic [Zn4 (Bim)4 ]4+ (Bim=[BH(im)3 ]- ; im=imidazole) cubic cages. Chiral transfer is observed from enantiopure (Zr4 L6 )8- cage to enantiopure [Zn4 (Bim)4 ]4+ cage. A pair of enantiomers (PTC-373(Δ) and PTC-373(Λ)) are formed. PTC-373 exhibits high chemical and thermal stabilities, affording an interesting single-crystal-to-single-crystal transformation. More importantly, the combination of ionic pair cages significantly enhances its third-order nonlinear optical property, and its thin-film exhibits an excellent optical limiting effect.

Designed metal-organic π-clusters combining the aromaticity of the metal cluster and ligands for a third-order nonlinear optical response.

The pivotal role of clusters and aromaticity in chemistry is undeniable, but there remains a gap in systematically understanding the aromaticity of metal-organic clusters. Herein, this article presents a novel metal-organic π-cluster, melding both metal-organic chemistry and aromaticity, to guide the construction of structurally stable Os-organic π-clusters. An in-depth analysis of these clusters reveals their bonding attributes, π-electronic composition, and origins of aromaticity, thereby confirming their unique metal-organic π-cluster properties. Furthermore, the Os5 cluster exhibits a promising third-order nonlinear optical (NLO) response, attributable to its narrow band gap and uniform electron/hole distribution, suggesting its potential as an optical switching material. This research introduces a fresh perspective on clusters, centered on delocalization, and broadens the domain of aromaticity studies. It also presents a novel method for designing efficient third-order NLO materials through consideration of the structure-activity relationship.

Bioinspired Polyoxo-titanium Cluster for Greatly Enhanced Solar-Driven CO2 Reduction.

Developing artificial enzymes with excellent catalytic activities and uncovering the structural and chemical determinants remain a grand challenge. Discrete titanium-oxo clusters with well-defined coordination environments at the atomic level can mimic the pivotal catalytic center of natural enzymes and optimize the charge-transfer kinetics. Herein, we report the precise structural tailoring of a self-assembled tetrahedral Ti4Mn3-cluster for photocatalytic CO2 reduction and realize the selective evolution of CO over specific sites. Experiments and theoretical simulation demonstrate that the high catalytic performance of the Ti4Mn3-cluster should be related to the synergy between active Mn sites and the surrounding functional microenvironment. The reduced energy barrier of the CO2 photoreduction reaction and moderate adsorption strength of CO* are beneficial for the high selective evolution of CO. This work provides a molecular scale accurate structural model to give insight into artificial enzyme for CO2 photoreduction.

Enhancing the photocatalytic efficiency of two-dimensional aluminum nitride materials through strategic rare earth doping.

Two-dimensional (2D) materials demonstrate promising potential as high-efficiency photocatalysts. However, the intrinsic limitations of aluminum nitride (AlN), such as inadequate oxidation capacity, a high carrier recombination rate, and limited absorption of visible light, pose considerable challenges. In this paper, we introduce a novel co-doping technique with dysprosium (Dy) and carbon (C) on a 2D AlN monolayer, aiming to enhance its photocatalytic properties. Our first-principles calculations reveal a reduction in the bandgap and a significant enhancement in the visible light absorption rate of the co-doped Al24N22DyC2 structure. Notably, the distribution of the highest occupied molecular orbital and the lowest unoccupied molecular in proximity to Dy atoms demonstrates favorable conditions for carrier separation. Theoretical assessments of the hydrogen evolution reaction and oxygen evolution reaction activities further corroborate the potential of Al24N22DyC2 as a competent catalyst for photocatalytic reactions. These findings provide valuable theoretical insights for the experimental design and fabrication of novel, high-efficiency AlN semiconductor photocatalysts.

Ligand-dependent structural diversity and optimizable CO2 chemical fixation activities of Cu-doped polyoxo-titanium clusters.

Heterometallic oxo clusters have been attracting intensive interest due to their unique properties originating from the synergistic interactions between different components. Herein, we report the construction and catalytic applications of a family of copper-doped polyoxo-titanium clusters (Cu-PTCs) coordinated with different acetate derivative ligands. The solvothermal reactions of metal salts and trimethylacetic acid or 1,2-phenylenediacetic acid in ethanol produced Ti6Cu3(µ3-O)4(µ2-O)(OEt)16(L1)4 (L1 = trimethyl acetate, PTC-367) and H2Ti8Cu2Br2(µ4-O)2(µ2-O)4(OEt)20(L2)2 (L2 = 1,2-phenylenediacetate, PTC-368), respectively. When smaller acetic acid was introduced as a stabilizing ligand, higher nuclei H2Ti16Cu3(µ4-O)5(µ3-O)15(µ2-O)3(OiPr)18(Ac)8 (Ac = acetate, PTC-369) and H3Ti29Cu3(µ4-O)6(µ3-O)30(µ2-O)8(OiPr)17(Ac)20 (PTC-370) were prepared. The number of metal ions exposed on the surface of the four clusters changes due to variations in the steric hindrance of functionalizing ligands, and theoretically, so does their catalytic activity as Lewis acids. In light of this, we conducted a carbon dioxide cycloaddition reaction in an atmospheric environment and the four obtained compounds displayed increasing catalytic activities from PTC-367 to PTC-370. These results provide a feasible synthetic method for modulating the structures of Cu-doped titanium oxide materials and improving their catalytic activities.

Predict the Polarizability and Order of Magnitude of Second Hyperpolarizability of Molecules by Machine Learning.

In order to determine the polarizability and hyperpolarizability of a molecule, several key parameters need to be known, including the excitation energy of the ground and excited states, the transition dipole moment, and the difference of dipole moment between the ground and excited states. In this study, a machine-learning model was developed and trained to predict the molecular polarizability and second-order hyperpolarizability on a subset of QM9 data set. The density of states was employed as input to the model. The results demonstrated that the machine-learning model effectively estimated both polarizability and the order of magnitude of second-order hyperpolarizability. However, the model was unable to predict the dipole moment and first-order hyperpolarizability, suggesting limitations in its ability to predict the difference of dipole moment between the ground and excited states. The computational efficiency of machine-learning models compared to traditional quantum mechanical calculations enables the possibility of large-scale screening of molecules that satisfy specific requirements using existing databases. This work presents a potential solution for the efficient exploration and analysis of molecules on a larger scale.

A Humidity-Induced Large Electronic Conductivity Change of 107 on a Metal-Organic Framework for Highly Sensitive Water Detection.

The electronic conductivity (EC) of metal-organic frameworks (MOFs) is sensitive to strongly oxidizing guest molecules. Water is a relatively mild species, however, the effect of H2 O on the EC of MOFs is rarely reported. We explored the effect of H2 O on the EC in the MOFs (NH2 )2 -MIL-125 and its derivatives with experimental and theoretical investigations. Unexpectedly, a large EC increase of 107 on H2 SO4 @(NH2 )2 -MIL-125 by H2 O was observed. Brønsted acid-base pairs formed with the -NH2 groups, and H2 SO4 played an important role in promoting the charge transfer from H2 O to the MOF. Based on H2 SO4 @(NH2 )2 -MIL-125, a high-performance chemiresistive humidity sensor was developed with the highest sensitivity, broadest detection range, and lowest limit of detection amongst all reported sensing materials to date. This work not only demonstrated that H2 O can remarkably influence the EC of MOFs, but it also revealed that post-modification of the structure of MOFs could enhance the influence of the guest molecule on their EC to design high-performance sensing materials.

Dangling bond formation on COF nanosheets for enhancing sensing performances.

Dangling bond formation for COF materials in a rational manner is an enormous challenge, especially through post-treatment which is a facile strategy while has not been reported yet. In this work, a "chemical scissor" strategy is proposed for the first time to rationally design dangling bonds in COF materials. It is found that Zn2+ coordination in post-metallization of TDCOF can act as an "inducer" which elongates the target bond and facilitates its fracture in hydrolyzation reactions to create dangling bonds. The number of dangling bonds is well-modulated by controlling the post-metallization time. Zn-TDCOF-12 shows one of the highest sensitivities to NO2 in all reported chemiresistive gas sensing materials operating under visible light and room temperature. This work opens an avenue to rationally design a dangling bond in COF materials, which could increase the active sites and improve the mass transport in COFs to remarkably promote their various chemical applications.

Overcoming the Trade-Off between C2 H2 Sorption and Separation Performance by Regulating Metal-Alkyne Chemical Interaction in Metal-Organic Frameworks.

Designing porous materials for C2 H2 purification and safe storage is essential research for industrial utilization. We emphatically regulate the metal-alkyne interaction of PdII and PtII on C2 H2 sorption and C2 H2 /CO2 separation in two isostructural NbO metal-organic frameworks (MOFs), Pd/Cu-PDA and Pt/Cu-PDA. The experimental investigations and systematic theoretical calculations reveal that PdII in Pd/Cu-PDA undergoes spontaneous chemical reaction with C2 H2 , leading to irreversible structural collapse and loss of C2 H2 /CO2 sorption and separation. Contrarily, PtII in Pt/Cu-PDA shows strong di-σ bond interaction with C2 H2 to form specific π-complexation, contributing to high C2 H2 capture (28.7 cm3 g-1 at 0.01 bar and 153 cm3 g-1 at 1 bar). The reusable Pt/Cu-PDA efficiently separates C2 H2 from C2 H2 /CO2 mixtures with satisfying selectivity and C2 H2 capacity (37 min g-1 ). This research provides valuable insight into designing high-performance MOFs for gas sorption and separation.

Pore Size Modulation in Flexible Metal-Organic Framework Enabling High Performance Gas Sensing.

Pore size plays a critical role in determining the performance of metal-organic frameworks (MOFs) in catalysis, sensing, and gas storage or separation. However, revealing the pore-size/property relationship remains extremely challenging because ideal structure models possessing different pore sizes but having the same components are lacking. In this work, a solvent-coordination directed structure swelling method was developed for modulating the ratio between the large and narrow pore phases of a flexible MOF, MIL-88B. Pore-size-dependent gas sensitivity and selectivity were studied for the first time in the MIL-88B samples. The optimized MIL-88B-20 % sample showed one of the best sensing performances among all the reported MOF-based H2 S-sensing materials. This work not only provides a method to synthesize ideal structure models for revealing the relationship between pore-size and properties, but also may inspire the development of high-performance gas sensing materials.

Green, General and Low-cost Synthesis of Porous Organic Polymers in Sub-kilogram Scale for Catalysis and CO2 Capture.

Porous organic polymers (POPs) with high porosity and tunable functionalities have been widely studied for use in gas separation, catalysis, energy conversion and energy storage. However, the high cost of organic monomers, and the use of toxic solvents and high temperatures during synthesis pose obstacles for large-scale production. Herein, we report the synthesis of imine and aminal-linked POPs using inexpensive diamine and dialdehyde monomers in green solvents. Theoretical calculations and control experiments show that using meta-diamines is crucial for forming aminal linkages and branching porous networks from [2+2] polycondensation reactions. The method demonstrates good generality in that 6 POPs were successfully synthesized from different monomers. Additionally, we scaled up the synthesis in ethanol at room temperature, resulting in the production of POPs in sub-kilogram quantities at a relatively low cost. Proof-of-concept studies demonstrate that the POPs can be used as high-performance sorbents for CO2 separation and as porous substrates for efficient heterogeneous catalysis. This method provides an environmentally friendly and cost-effective approach for large-scale synthesis of various POPs.

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.

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.

Porphyrin metal-organic frameworks with bilayer and pillar-layered frameworks and third-order nonlinear optical properties.

It is recognized that dimensions have a decisive influence on the properties of materials. Metal-organic frameworks as third-order nonlinear optical (NLO) materials have attracted much attention recently. However, research on the influence of dimensions on third-order NLO properties of MOFs has not been reported. In this work, we synthesized two porphyrin MOFs (PMOFs) constructed with π-conjugated tetracarboxyphenylporphyrin (TCPP) and in situ formed 1,2-bis(1H-benzo[d]imidazol-2-yl)ethene (BIE) conjugated ligands. In both PMOFs, Zn2(CO2)4 paddlewheel units are connected by TCPP-Zn ligands to form a 2D layer. Interestingly, these layers are linked by BIE ligands to form a bilayer in PMOF-1 and a 3D pillar-layered framework in PMOF-2, which serve as structural models to evaluate the influence of dimensions on third-order NLO properties. It is speculated that the 3D pillar-layered framework in PMOF-2 with BIE conjugated pillars is more conducive to interlayer charge transfer than the two-dimensional bilayer in PMOF-1, thus achieving a better third-order NLO performance. The third-order NLO test results of PMOFs in a polydimethylsiloxane (PDMS) matrix showed that PMOF-2 displayed a higher nonlinear absorption coefficient, large third-order susceptibility and lower limiting threshold than PMOF-1/PDMS, which may be mainly attributed to the fact that the 3D pillar-layered framework is more conducive to interlayer charge transfer than the two-dimensional bilayer. This work reveals the influence of dimensions on third-order nonlinear properties which will help to explore new MOF materials with excellent third-order NLO properties.

Cu4Ti4-oxo clusters functionalized by in situ - generated 2,2'-biphenolate ligands from the oxidative coupling of phenols.

Herein, we report a twisted cubic Cu(I)4Ti(IV)4-oxo cluster stabilized by in situ - formed 2,2'-biphenolate ligands from the oxidative coupling of phenols. The 2,2'-biphenolate-functionalized Cu(I)4Ti(IV)4O4 cluster shows short Cu⋯C contacts and exhibits smaller HOMO-LUMO gaps than those of reported Ti(IV)4O4.

Data-driven generation of mixed X-anion perovskite properties.

Mixed X-anion perovskites, such as CsPbX3 (X = Cl, Br, or I), play an important role in photovoltaic applications. The massive disordered structures associated with mixed anions produce the need for property calculations. However, traditional density functional theory (DFT) computational tools are limited by their computational efficiency to generate the properties of a large number of structures quickly. Researchers have proposed supervised deep learning to forecast crystal properties. For such a supervised convolutional neural network (CNN), we introduce an adversarial loss function that allows for consistent or lower errors with a fewer samples. Meanwhile, we have trained parameterized quantum circuits (PQCs) of CNNs and auto-encoder networks for extracting structural representations. PQCs of deep learning, also named quantum deep learning or quantum machine learning, have been first applied in the research of perovskites and obtained an RMSE (root mean squared error) of less than 1 meV. Our work demonstrates that adversarial learning training mechanisms and PQC-based quantum deep learning will emerge for extensive and deep exploration of data-driven material formation prediction tasks.