Layer by Layer Spraying Fabrication of Aggregation-Induced Emission Metal-Organic Frameworks Thin Film

The development of new metal-organic frameworks (MOFs) thin films is important for expanding their functions and applications. Herein, we first report a new kind of MOF thin film by using aggregation-induced emission (AIE) dicarboxyl ligand through a liquid-phase epitaxial (LPE) layer-by-layer (LBL) spraying method (named AIE surface-coordinated metal-organic frameworks thin film, AIE-SURMOF). The obtained AIE-SURMOF Zn4O(TPE)3 (ZnTPE) has highly growth orientation and homogeneous thin film, showing strong fluorescent property. Furthermore, by loading chiral guest in the MOF pore, the formed chiral encapsulated AIE-SURMOF can clearly indicate obvious circularly polarized luminescence performance with glum of 0.01. This study provides new MOF thin film and new strategy for expanding function and application of MOF materials.

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.

Photo-Curable 3D Printing of Circularly Polarized Afterglow Metal-Organic Framework Monoliths

Developing coordination complexes (such as metal-organic frameworks, MOFs) with circularly polarized luminescence (CPL) is currently attracting tremendous attention and remains a significant challenge in achieving MOF with circularly polarized afterglow. Herein, MOFs-based circularly polarized afterglow is first reported by combining the chiral induction approach and tuning the afterglow times by using the auxiliary ligands regulation strategy. The obtained chiral R/S-ZnIDC, R/S-ZnIDC(bpy), and R/S-ZnIDC(bpe)(IDC = 1H-Imidazole-4,5-dicarboxylate, bpy = 4,4'-Bipyridine, bpe = trans-1,2-Bis(4-pyridyl) ethylene) containing a similar structure unit display different afterglow times with 3, 1, and <0.1 s respectively which attribute to that the longer auxiliary ligand hinders the energy transfer through the hydrogen bonding. The obtained chiral complexes reveal a strong chiral signal, obvious photoluminescence afterglow feature, and strong CPL performance (glum up to 3.7 × 10-2). Furthermore, the photo-curing 3D printing method is first proposed to prepare various chiral MOFs based monoliths from 2D patterns to 3D scaffolds for anti-counterfeiting and information encryption applications. This work not only develops chiral complexes monoliths by photo-curing 3D printing technique but opens a new strategy to achieve tunable CPL afterglow in optical applications.

Facile Synthesis of Novel Ti2 C Nano Bipyramids for Photothermal and Photodynamic Therapy of Breast Cancer

Photo-responsive synergetic therapeutics achieved significant attraction in cancer theranostic due to the versatile characteristics of nanomaterials. There have been substantial efforts in developing the simplest nano-design with exceptional synergistic properties and multifunctionalities. In this work, biocompatible Ti2 C MXene nano bipyramids (MNBPs) were synthesized by hydrothermal method with dual functionalities of photothermal and photodynamic therapies. The MNBPs shape was obtained from two-dimensional (2D) Ti2 C nanosheets by controlling the temperature of the reaction mixture. The structure of these Ti2 C MNBPs was characterized by a high-resolution transmission electron microscope, scanning electron microscope, atomic force microscope, X-ray photoelectron spectroscopy, and X-ray diffraction. The Ti2 C NBPs have shown exceptional photothermal properties with increased temperature to 72.3 °C under 808 nm laser irradiation. The designed nano bipyramids demonstrated excellent cellular uptake and biocompatibility. The Ti2 C NBP has established a remarkable photothermal therapy (PTT) effect against 4T1 breast cancer cells. Moreover, Ti2C NBPs showed a profound response to UV light (6 mW/cm2 ) and produced reactive oxygen species, making them useful for photodynamic therapy (PDT). These in-vitro studies pave a new path to tune the properties of photo-responsive MXene nanosheets, indicating a potential use in biomedical applications.

Anion-encapsulating, discrete prism and extended frusta, from trimetallated triangular macrocycles and linkers

Reaction of a trinuclear triangular macrocyclic complex Pb3L(CF3SO3)6 with bidentate linkers in a ratio of 3 equiv. of linker per 2 equiv. of complex, produces a prismatic structure with 4,4'-dipyridyl, and two unprecedented, extended 3D frustum-like structures with 1,2-di(4-pyridyl)ethylene and 1,4-di(4-pyridyl)benzene. The cavities of these structures encapsulate triflate anions.

Inducing Circularly Polarized Luminescence by Confined Synthesis of Ultrasmall Chiral Carbon Nanodot Arrays in Pyrene-Based MOF Thin Film

Combining the features of the host-guest system and chirality is an efficient strategy to achieve circularly polarized luminescence (CPL). Herein, well-defined chiral carbon nanodot (chirCND) arrays were confined-synthesized by low-temperature calcination of a chiral amino acid loaded metal-organic framework (MOF) to induce high CPL. An achiral porous pyrene-based MOF NU-1000 thin film as the host template was prepared by a liquid-phase epitaxial layer-by-layer fashion, and chiral amino acids as the carbon sources could be confined in the porous MOF and carbonized to homogeneous and ultrasmall chirCND arrays, resulting in a chirCNDs@NU-1000 thin film (l-CNDsx@NU-1000; x = l-cysteine (cys), l-serine, l-histidine, l-glutamic acid, and l-pyroglutamic acid). The results show the pristine chirCNDs by directly carbonizing chiral amino acids hardly endow them with a CPL property. By contrast, benefiting from the arrayed confinement and coordination interaction between chirCNDs and NU-1000, the chirality transfer on the excited state of chirCNDs@NU-1000 is enabled, leading to strong CPL performance (a high luminescence dissymmetry factor glum of l-CNDscys@NU-1000 thin film reached 1.74 × 10-2). This study of chirCNDs encapsulated in fluorescent MOF thin films provides a strategy for developing uniform chiral carbon nanoarrays and offers chiral host-guest thin-film materials for optical applications.

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.

Highly Efficient Light Helicity Detection of Enantiomers by Chiral Metal-Organic Framework Thin Films

The potential of chiral metal-organic frameworks (MOFs) for circularly polarized (CP) optics has been largely unexplored. Herein, we have successfully deposited monolithic and highly oriented chiral MOF thin films prepared by a layer-by-layer method (referred to as surface-coordinated MOF thin films, SURMOF) to fabricate CP photodetection devices and distinguish enantiomers. The helicity-sensitive absorption induced by a pair of enantiopure oriented SURMOF was found to be excellent, with an anisotropy factor reaching 0.41. Moreover, the chiral SURMOFs exhibited a pronounced difference in the uptake of the l- and d-tryptophan enantiomers. To demonstrate the potential of these novel MOF thin films for chirality analysis, we fabricated a portable sensor device that allows for chiral recognition by monitoring the photocurrent signals. Our findings not only introduce a new concept of using chiral building blocks for realizing direct CP photodetectors but also provide a blueprint for novel devices in chiral optics.

Erasable Photopatterning of Stilbene-Based Metal-Organic Framework Films

The development of photosensitive materials for erasable photopatterning is of significant interest in anti-counterfeiting and information storage applications. Herein two kinds of stilbene-based metal-organic framework (MOF) films with layer by layer method for studying photopatterning is reported. The resulting 2D Zn₂ (sdc)₂ MOF film (sdc = 4,4'-stilbenedicarboxylate) exhibits excellent photosensitive features with a very short photoconversion time (<35 s) while the 3D MOF Zn₄ O(sdc)₆ film does not have the property due to the fact that only parallel and short distance arrangement of olefin groups in the adjacent MOF layers can trigger [2+2] photocycloaddition. Furthermore, the Zn₂ (sdc)₂ film indicates obvious reversible fluorescent photoswitch behavior between yellow and blue fluorescence emission, which can achieve high-efficient, erasable photopatterning with various sizes (ca. 20 microns to decimeter). This study not only develops a new kind of photosensitive crystalline network film but also provides erasable photopatterning from macroscopic to microscopic in optical applications.

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.

Post-Assembly Modification of Homochiral Titanium-Organic Cages for Recognition and Separation of Molecular Isomers

A chiral metal-organic cage (MOC) was extended and fixed into a porous framework using a post-assembly modification strategy, which made it easier to study the host-guest chemistry of the solid-state MOC using a single-crystal diffraction technique. Anionic Ti₄ L₆ (L=embonate) cage can be used as a 4-connecting crystal engineering tecton, and its optical resolution was achieved, thus homochiral ΔΔΔΔ- and ΛΛΛΛ-[Ti₄ L₆ ] cages were obtained. Accordingly, a pair of homochiral cage-based microporous frameworks (PTC-236(Δ) and PTC-236(Λ)) were easily prepared by a post-assembly reaction. PTC-236 has rich recognition sites provided by the Ti₄ L₆ moieties, chiral channels and high framework stability, affording a single-crystal-to-single-crystal transformation for guest structure analyses. Thus it was successfully utilized for the recognition and separation of isomeric molecules. This study provides a new approach for the orderly combination of well-defined MOCs into functional porous frameworks.

Liquid-Phase Epitaxial Growth of Multiple MOF Thin Films with Highly Lattice Mismatch

The development of multiple metal-organic frameworks (MOFs) thin films with high lattice mismatches is still a challenging task. Herein we report a series of single and multiple (bi-varietal and tri-varietal)...

Ti3C2Tx-Modified PEDOT:PSS Hole-Transport Layer for Inverted Perovskite Solar Cells

PSS is a commonly used hole-transport layer (HTL) in inverted perovskite solar cells (PSCs) due to its compatibility with low-temperature solution processing. However, it possesses lower conductivity than other conductive polymers and metal oxides, along with surface defects, limiting its photovoltaic performance. In this study, we introduced two-dimensional Ti3C2Tx (MXene) as an additive in the PEDOT:PSS HTL with varying doping concentrations (i.e., 0, 0.03, 0.05, and 0.1 wt.%) to tune the electrical conductivity of PEDOT:PSS and to modify the properties of the perovskite film atop it. We noted that the grain size of the CH3NH3PbI3 (MAPI3) perovskite layer grown over an optimal concentration of MXene (0.03 wt.%)-doped PEDOT:PSS increased from 250 nm to 400 nm, reducing charge recombination due to fewer grain boundaries. Ultraviolet photoelectron spectroscopy (UPS) revealed increased work function (WF) from 4.43 eV to 4.99 eV with 0.03 wt.% MXene doping, making the extraction of holes easier due to a more favorable energy level alignment with the perovskite. Quantum chemical investigations based on density functional theory (DFT) were conducted at the ωB97XD/6-311++G(d,p) level of theory to provide more insight into the stability, bonding nature, and optoelectronic properties of the PEDOT:PSS-MXene system. The theoretical investigations revealed that the doping of PEDOT:PSS with Ti3C2Tx could cause a significant effect on the electronic properties of the HTL, as experimentally demonstrated by an increase in the electrical conductivity. Finally, the inverted PSCs employing 0.03 wt.% MXene-doped PEDOT:PSS showed an average power conversion efficiency (PCE) of 15.1%, up from 12.5% for a reference PSC employing a pristine PEDOT:PSS HTL. The champion device with a 0.03 wt.% MXene-PEDOT:PSS HTL achieved 15.5% PCE.

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.

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.

A Novel Cerium(IV)-Based Metal-Organic Framework for CO2 Chemical Fixation and Photocatalytic Overall Water Splitting

Cerium (IV)-based metal-organic frameworks (MOFs) are highly desirable due to their unique potential in fields such as redox catalysis and photocatalysis. However, due to the high reduction potential of Ce^IV species in solution, it is still a great challenge to synthesize Ce^IV -MOFs with novel structures, which are extremely dominated by the hexanuclear Ce-O cluster inorganic building units (IBUs). Herein, a Ce-O IBU chain containing Ce^IV -MOF, CSUST-3 (CSUST: Changsha University of Science and Technology), was successfully prepared using the kinetic stabilization study of UiO-66(Ce)-NDC (H₂ NDC=2,6-naphthalenedicarboxylic acid). Furthermore, owing to the superior redox activity, Lewis acidity and semiconductor-like behavior owing to Ce⁴⁺ , activated CSUST-3 was demonstrated to be an excellent catalyst for CO₂ chemical fixation. One-pot synthesis of styrene carbonate from styrene and CO₂ was achieved under mild conditions (1 atm CO₂ , 80 °C, and solvent free). Moreover, activated CSUST-3 was shown to be a remarkable co-catalyst-free photocatalyst for overall water splitting (OWS), rendering 59 μmol g^-1  h^-1 of H₂ and 22 μmol g^-1  h^-1 of O₂ under simulated sunlight irradiation (Na₂ S-Na₂ SO₃ as sacrificial agent).

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.

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.

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.

A metal-porphyrinic framework film as an efficient optical limiting layer in an electro-optical switchable device

Herein we report a 2D surface-coordinated porphyrinic metal-organic framework film (SURMOF) CuTCPP prepared by a layer by layer method as an optical limiting layer in a polymer-dispersed liquid crystal (PDLC) device. The results show that the CuTCPP SURMOF/PDLC device has excellent switchable transparency and optical limiting performance, providing a new route to achieve mutilfunctional electro-optical applications.

Surface chiroselective assembly of enantiopure crystalline porous films containing bichiral building blocks

The development of chiral crystalline porous materials (CPMs) containing multiple chiral building blocks plays an important role in chiral chemistry and applications but is a challenging task. Herein, we report the first example of bichiral building block based enantiopure CPM films containing metal-organic cages (MOCs) and metal complexes. The functionalized substrate was immersed subsequently into homochiral metal complex (R)- or (S)-Mn(DCH)3 (DCH = 1,2-diaminocyclohexane) and racemic Ti4L6 cage (L = embonate) solutions by a layer-by-layer growth method. During the assembly process, the substrate surface coordinated with (R)- or (S)-Mn(DCH)3 can, respectively, layer-by-layer chiroselectively connect Δ- or Λ-Ti4L6 cages to form homochiral (R, Δ)- or (S, Λ)-CPM films with a preferred [111] growth orientation, tunable thickness and homogeneous surface. The resulting enantiopure CPM films show strong chirality, photoluminescence, and circularly polarized luminescence (CPL) properties as well as good enantioselective adsorption toward enantiomers of 2-butanol and methyl-lactate. The present in situ surface chiroselective strategy opens a new route to assemble homochiral CPM films containing multiple chiral building blocks for chiral applications.

Host-Guest Thin Films by Confining Ultrafine Pt/C QDs into Metal-Organic Frameworks for Highly Efficient Hydrogen Evolution

Combining the features of host templates and guest species is an efficient strategy to optimize the photo/electrocatalytic performance. Herein, novel host-guest thin-film electrocatalysts are designed and developed with Pt doped carbon (Pt/C) confined into porphyrin-based metal-organic frameworks (MOFs). Porous MOF PCN-222 and PCN-221 thin films are used as the host templates and fabricated using vapor-assisted deposition method, and then the guest Pt/C quantum dots are encapsulated into the MOFs by loading the glucose mixed H₂ PtCl₆ and heating at 200 °C. Thanks to the confinement effect of MOF pores, the homogenous and ultrafine Pt/C nanowires (Pt/CNWs) and nanodots (Pt/CNDs) are confined in nanochannels of PCN-222 and nanocages of PCN-221 (Pt/CNW@PCN-222 and Pt/CND@PCN-221), respectively. The electrocatalytic study shows that the host-guest thin films have highly-efficient electrocatalytic hydrogen evolution performance under light irradiation. Furthermore, the time-resolved photoluminescent results reveal that Pt/CNW@PCN-222 has a faster charge transfer (441 ps) from PCN-222 to Pt/CNWs comparing to that (557 ps) of Pt/CND@PCN-221, indicating the guests with different shapes play an important role in the electrocatalytic performance. This work serves to present both the outstanding level of control in the precise synthesis and high potential for nanocomposite thin films in photo-electrocatalytic application.

N-Heterocyclic Carbene as a Surface Platform for Assembly of Homochiral Metal-Organic Framework Thin Films in Chiral Sensing

N-heterocyclic carbenes (NHCs) have attracted increasing attention on surface assembly due to their strong metal binding property, but an NHC-modified metal surface as a new growth platform to assemble other functional materials is still a challenge. Here, we report the preparation and chiral sensing properties of homochiral metal-organic framework thin films on carboxyl-containing NHC self-assembled monolayer-modified gold (Au(NHC)) substrates. By using a liquid-phase epitaxial layer-by-layer method, enantiopure [Cu₂(cam)₂dabco]_n thin films with preferred [110] crystal orientation have been successfully grown on Au(NHC) surfaces. The results of electrochemical cyclic voltammetry and quartz crystal microbalance uptakes of (R)- and (S)-1-phenylethanol show that the chiral porous thin film on the robust Au(NHC) surface has good enantiomeric electrochemical recognition and enantioselective adsorption. The present work is a new step to develop metal-NHCs as surface platforms for the preparation of multifunctional thin films for sensing applications.

Surface-coordinated metal-organic framework thin films (SURMOFs) for electrocatalytic applications

The design and development of highly efficient electrocatalysts are very important in energy storage and conversion. As a kind of inorganic organic hybrid material, metal-organic frameworks (MOFs) have been used as electrocatalysts in electrocatalytic reactions due to their structural diversities and fascinating functionalities. Particularly, MOF thin films are coordinated on substrate surfaces by a liquid phase epitaxial (LPE) layer by layer (LBL) growth method (called surface-coordinated MOF thin films, SURMOFs), and recently have been studied in various applications due to their precisely controlled thickness, preferred growth orientation and homogeneous surface. In this review, we will summarize the preparation and electrocatalysis of SURMOFs and their derived thin films (SURMOF-D). The SURMOF based thin films possess diverse topological structures and flexible properties, providing abundant catalytically active sites and fast charge transfer for efficient electrocatalytic performance in the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CRR), supercapacitors, tandem electrocatalysis and so on. The research challenges and problems of SURMOFs for electrocatalytic applications are also discussed at the end of the review.

Auto-controlled fabrication of a metal-porphyrin framework thin film with tunable optical limiting effects

Metal-organic frameworks (MOFs) with third-order nonlinear optical (NLO) properties are still in their infancy but are very important. In this work, we first develop a layer by layer autoarm immersion method for preparing porphyrin-based MOF (PIZA-1) thin films with third-order NLO properties. By precisely controlling the thickness, the nonlinear absorption of PIZA-1 thin films can be switched continuously between reverse saturable absorption (RSA) and saturable absorption (SA) by using the Z-scan technique. In addition, the optical limiting effect could be further optimized by loading C₆₀ in the pores of the PIZA-1 thin film. These findings not only open a new route for the exploitation of third-order NLO thin film materials, but also offer an insightful understanding of porphyrin-based MOF thin films for future broad practical applications.

Epitaxial Growth of Highly Transparent Metal-Porphyrin Framework Thin Films for Efficient Bifacial Dye-Sensitized Solar Cells

Bifacial dye-sensitized solar cells (DSSCs) are regarded as promising solar energy conversion devices with high efficiency and less resource consumption. In this work, a highly transparent and efficient counter electrode (CE) is fabricated by introducing highly dispersed single Pt atoms doped into the van der Waals layer-by-layer epitaxially grown Zn-TCPP thin film (Zn-TCPP-Pt). The resulting Zn-TCPP-Pt CE has similar catalytic activity to commercial Pt CE but shows a better light transmission capacity in the range of visible light. The bifacial DSSC with Zn-TCPP-Pt thin film CE achieves high power conversion efficiencies of 5.48 and 4.88% under front-side and rear-side irradiation, respectively. With maximized atomic efficiency, excellent performance was obtained with about 1% Pt content and highly transparent CEs. Therefore, the light energy resource utilization rate of such less Pt and transparence CE is greatly improved in bifacial dye-sensitized solar cells, making it a promising candidate to replace Pt CE.

Liquid-Phase Epitaxial Growth of Azapyrene-Based Chiral Metal-Organic Framework Thin Films for Circularly Polarized Luminescence

Development of chiral metal-organic frameworks (MOFs) for circularly polarized luminescence (CPL) is a challenging but important task. In this work, we report a first example of azapyrene-based chiral MOF thin films [Zn₂Cam₂DAP]_n grown on functionalized substrates (named SURchirMOF-4) for CPL property. By using a liquid-phase epitaxial layer-by-layer method, the resulted SURchirMOF-4 was constructed from chiral camphoric acid and 2,7-diazapyrene ligand, which has high orientation and homogeneity. The circular dichroism, CPL, and enantioselective adsorption results show that SURchirMOF-4 has strong chirality and CPL property as well as good enantioselective adsorption toward enantiomers of methyl-lactate. The synthesis of azapyrene-based chiral MOF thin films not only represents an ideal model for studying the enantioselective adsorption, but also will be a valuable approach for development of the chiral thin film exhibiting CPL property.

Helical carbon tubes derived from epitaxial Cu-MOF coating on textile for enhanced supercapacitor performance

A new helical carbon tube material has been prepared from epitaxial Cu-MOF coating on textile by calcination treatment.

Electrooxidation of Pd–Cu NP loaded porous carbon derived from a Cu-MOF

We have synthesized Pd–Cu NP loaded porous carbon through the direct carbonization of a porous Cu based MOF for efficient electrooxidation.

Chiral and kryptoracemic Dy(iii) complexes with field-induced single molecule magnet behavior

Crystalline mode modulation and magnetic relaxation manipulation can be realized by the introduction of different anions into mononuclear Dy(iii) single molecule magnets (SMMs).

Single molecule magnetic behaviour in lanthanide naphthalenesulfonate complexes

A family of mononuclear lanthanide complexes exhibiting slow magnetic relaxation is reported, providing the first examples of pure 4f sulfonate-based single molecule magnets.

Insight into the epitaxial encapsulation of Pd catalysts in an oriented metalloporphyrin network thin film for tandem catalysis

A palladium catalyst (Pd-Cs) encapsulated metalloporphyrin network PIZA-1 thin film with bifunctional properties has been developed through a modified epitaxial layer-by-layer encapsulation approach. Combining the oxidation activity of Pd-Cs and the acetalization activity of the Lewis acidic sites in the PIZA-1 thin film, this bifunctional catalyst of the Pd-Cs@PIZA-1 thin film exhibits a good catalytic activity in a one-pot tandem oxidation-acetalization reaction. Furthermore, the surface components can be controlled by ending the top layer with different precursors in the thin film preparation procedures. The catalytic performances of these thin films with different surface composites were studied under the same conditions, which showed different reaction conversions. The result revealed that the surface component can influence the catalytic performance of the thin films. This epitaxial encapsulation offers a good understanding of the tandem catalysis for thin film materials and provides useful guidance to develop new thin film materials with catalytic properties.

Epitaxial Growth of Oriented Metalloporphyrin Network Thin Film for Improved Selectivity of Volatile Organic Compounds

This study reports an oriented and homogenous cobalt-metalloporphyrin network (PIZA-1) thin film prepared by liquid phase epitaxial (LPE) method. The thickness of the obtained thin films can be well controlled, and their photocurrent properties can also be tuned by LPE cycles or the introduction of conductive guest molecules (tetracyanoquinodimethane and C₆₀ ) into the PIZA-1 pores. The study of quartz crystal microbalance adsorption confirms that the PIZA-1 thin film with [110]-orientation presents much higher selectivity of benzene over toluene and p-xylene than that of the PIZA-1 powder with mixed orientations. These results reveal that the selective adsorption of volatile organic compounds highly depends on the growth orientations of porphyrin-based metal-organic framework thin films. Furthermore, the work will provide a new perspective for developing important semiconductive sensing materials with improved selectivity of guest compounds.

Epitaxial Growth of MOF Thin Film for Modifying the Dielectric Layer in Organic Field-Effect Transistors

Metal-organic framework (MOF) thin films are important in the application of sensors and devices. However, the application of MOF thin films in organic field effect transistors (OFETs) is still a challenge to date. Here, we first use the MOF thin film prepared by a liquid-phase epitaxial (LPE) approach (also called SURMOFs) to modify the SiO₂ dielectric layer in the OFETs. After the semiconductive polymer of PTB7-Th (poly[4,8-bis(5-(2-ethylhexyl)thiophene-2-yl)benzo[1,2-b:4,5-b']dithiophene-co-3-fluorothieno[3,4-b]thiophene-2-carboxylate]) was coated on MOF/SiO₂ and two electrodes on the semiconducting film were deposited sequentially, MOF-based OFETs were fabricated successfully. By controlling the LPE cycles of SURMOF HKUST-1 (also named Cu₃(BTC)₂, BTC = 1,3,5-benzenetricarboxylate), the performance of the HKUST-1/SiO₂-based OFETs showed high charge mobility and low threshold voltage. This first report on the application of MOF thin film in OFETs will offer an effective approach for designing a new kind of materials for the OFET application.

Synthesis of homochiral zeolitic metal–organic frameworks with amino acid and tetrazolates for chiral recognition

By mixing amino acids and tetrazolate ligands, a series of homochiral zeolitic metal–organic frameworks (ZMOFs) with ABW topology have been synthesized, which show permanent microporosity and potential enantioselective recognition ability.

Surface-mounted MOF templated fabrication of homochiral polymer thin film for enantioselective adsorption of drugs

A chiral porous polymer thin film has been prepared using a template of SURMOF, showing an enantioselective adsorption of naproxen.

A Confined Fabrication of Perovskite Quantum Dots in Oriented MOF Thin Film

Organic-inorganic hybrid lead organohalide perovskites are inexpensive materials for high-efficiency photovoltaic solar cells, optical properties, and superior electrical conductivity. However, the fabrication of their quantum dots (QDs) with uniform ultrasmall particles is still a challenge. Here we use oriented microporous metal-organic framework (MOF) thin film prepared by liquid phase epitaxy approach as a template for CH₃NH₃PbI₂X (X = Cl, Br, and I) perovskite QDs fabrication. By introducing the PbI₂ and CH₃NH₃X (MAX) precursors into MOF HKUST-1 (Cu₃(BTC)₂, BTC = 1,3,5-benzene tricarboxylate) thin film in a stepwise approach, the resulting perovskite MAPbI₂X (X = Cl, Br, and I) QDs with uniform diameters of 1.5-2 nm match the pore size of HKUST-1. Furthermore, the photoluminescent properties and stability in the moist air of the perovskite QDs loaded HKUST-1 thin film were studied. This confined fabrication strategy demonstrates that the perovskite QDs loaded MOF thin film will be insensitive to air exposure and offers a novel means of confining the uniform size of the similar perovskite QDs according to the oriented porous MOF materials.

Chiral Chemistry of Homochiral Porous Thin Film with Different Growth Orientations

Chirality is one of the essential features in our living life and exerts a wide variety of applications in enantio-adsorption/separation. However, the mechanism between chirality and enantio-adsorption/separation is very significant in homochiral porous materials; in particular, the understanding of the relationship between crystalline orientations and chiral behavior is a challenging but important mechanism. In this work, homochiral porous crystalline metal organic framework (MOF) materials were grown on hydroxyl- and carboxyl-functionalized substrates, resulting in homochiral porous thin films with different orientations. The enantioselectivity and adsorption rates in two different oriented homochiral porous thin films were studied by using gas-phase quartz crystal microbalance (QCM) experiment of chiral probe molecules. The different mass uptake and time constant showed that the chiral behavior can be obviously influenced by the crystalline orientations on the same homochiral porous thin films. This study will not only offer a good model to understand the mechanism of chiral behavior in homochiral porous materials but also provide guidance for developing new homochiral-oriented porous thin films with high enantioselectivity or enantioseparation.

Chiral chemistry of metal-camphorate frameworks

This critical review presents the various synthetic approaches and chiral chemistry of metal-camphorate frameworks (MCamFs), which are homochiral metal-organic frameworks (MOFs) constructed from a camphorate ligand. The interest in this unique subset of homochiral MOFs is derived from the many interesting chiral features for both materials and life sciences, such as asymmetrical synthesis or crystallization, homochiral structural design, chiral induction, absolute helical control and ligand handedness. Additionally, we discuss the potential applications of homochiral MCamFs. This review will be of interest to researchers attempting to design other homochiral MOFs and those engaged in the extension of MOFs for applications such as chiral recognition, enantiomer separation, asymmetric catalysis, nonlinear sensors and devices.

Enantioselective adsorption in homochiral metal-organic frameworks: the pore size influence

Uptake experiments in thin films of isoreticular chiral MOFs of type Cu2(Dcam)2(L) with identical stereogenic centers but different pore dimensions show that the enantioselectivity is significantly influenced by the pore size. The highest selectivity was found for medium pore sizes, roughly corresponding to the extension of the chiral guest molecule, limonene.

Chiral Porous Metacrystals: Employing Liquid-Phase Epitaxy to Assemble Enantiopure Metal-Organic Nanoclusters into Molecular Framework Pores

We describe the fabrication of hybrid yet well-ordered porous nanoparticle (NP) arrays with full three-dimensional periodicity by embedding nanometer-sized metal-organic clusters (MOCs) into metal-organic frameworks (MOFs). Although conventional NP@MOF encapsulation procedures failed for these fairly large (1.66 nm diameter) NPs, we achieved maximum loading efficiency (one NP per pore) by using a modified liquid phase epitaxy (LPE) layer-by-layer approach to grow and load the MOF. The preformed NPs, homochiral Ti4(OH)4(R/S-BINOL)6 clusters (Ti-MOC, BINOL = 1,1'-bi-2-naphthol), formed a regular lattice inside the pores of an achiral HKUST-1 (or Cu3(BTC)2, BTC = 1,3,5-benzenetricarboxylate) MOF thin film. Exposure to the different enantiomers of methyl lactate revealed that the NP@MOF metacrystal is quite efficient regarding enantiomer recognition and separation. The approach presented here is also suited for other MOF types and expected to provide a substantial stimulus for the fabrication of metacrystals, crystalline solids made from nanoparticles instead of atoms.