Metal Organic Framework Thin Films Research Articles

Recent Advances in Lanthanide Metal–Organic Framework Thin Films Based on Eu, Tb, Gd: Preparation and Application as Luminescent Sensors and Light-Emitting Devices

Lanthanide Metal–Organic Frameworks (LnMOFs), in recent years, have developed into an interesting subclass of MOFs. While the number of published papers, in particular, were dedicated to their synthesis and functional properties, along with the application mechanisms of MOFs, only a few of them have been focused on LnMOFs thin films independently. LnMOFs have become interesting thanks to their outstanding properties, for example, excellent structural flexibility, tunable pore size, surface area, functionality, and good chemical stability. Significant progress over the past two decades in the preparation of MOF films has been achieved, especially towards the development of green, or at least greener, synthesis approaches. We begin with insight into various types of MOFs and summarize recent achievements in the production of LnMOF films, along with various film preparation approaches. Afterward, we briefly discuss the applications of luminescence features of lanthanide ions in films and their potential as white-light source materials. We also covered films based on Eu, Tb, and Gd with particular accents on different design approaches. Moreover, specifically, luminescent features applied for sensing temperature, a variety of ions, gases, and biomolecules are highlighted. The review ends with a comprehensive conclusion about the state-of-art-potential of LnMOFs together with an outlook on the future of LnMOF films in future technologies.

Morphology-dependent optical properties of a 3D CH3NH3PbBr3 based metal − organic framework

More recently, Metal–Organic Frameworks (MOFs) have displayed extensive promise in the fields of energy storage, solar cells, catalysis, super capacitors, and optoelectronic devices. This work investigates the nonlinear thermo-optical responses of CH3NH3PbBr3 (MAPbBr3) and mix MAPbBr3 with UiO-66-NH2 (MAPbBr3 + MOF) thin films using the Z-scan technique with different incident power of laser ranging from 10 mW to 50 mW. The results show that the third-order nonlinear optical coefficients of MAPbBr3 + MOF thin films were improved obviously than MAPbBr3 thin films. Furthermore, nonlinear optical properties of MAPbBr3 + MOF thin film is evaluated to be improved from 12.5 × 10-8 to 38.2 × 10-8 by decreasing the input power of laser from 50 mW to 10 mW. This treatment repeated for MAPbBr3 thin film, as well. Considering Kubelka-Munk equation, energy gap) Eg for the MAPbBr3 and MAPbBr3 + MOF thin films deposited on glass film is calculated to be 2.565 and 2.530 eV. Due to analyze the optical characterization of the synthesized samples, optical reflection, transmission and absorption were studied. Kramers-Kronig relations and the reflectance data were used for calculation of complex refractive index and dielectric constant. The transverse and the longitudinal optical phonon modes of MAPbBr3 and MAPbBr3 + MOF thin films locate at about 548 and 598 nm, and 590 and 640 nm, respectively. This research opens a new window for wide scale optoelectronic devices in Q-switching for the generation of pulsed lasers including MAPbBr3 with UiO-66-NH2 by detecting the remarkable nonlinear optical characteristics in lower incident power.

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.

Electrochemical deposition of Pyrazine-Templated 2D Ru@MOFs nanosheets for sensitive electrochemiluminescent immunoassay of classical swine fever virus

Electrochemical deposition technique for room-temperature fabrication of functionalized metal–organic frameworks (MOFs) have attracted increasing attention in many important applications. Herein, a sensitive electrochemiluminescent (ECL) immunosensor was fabricated for the determination of classical swine fever virus (CSFV) based on electrochemical synthesis and deposition of pyrazine-templated ruthenium (II)-MOFs (Pyz-Ru@MOFs) thin films on the electrode surface. In this protocol, the 2D Pyz-Ru@MOFs nanosheets were synthesized under green water phase condition from the carboxyl-rich tris(4,4′-dicarboxylic acid-2,2′-bipyridyl) ruthenium(II) (Ru(dcbpy)32+) as ECL luminophore and organic ligand to coordinate with zinc ions, and pyrazine as a structure-directing agent to control the formation of sheetlike structure. Due to packaging plenty of Ru(dcbpy)32+ molecules in the frameworks, the mesoporous thin films of Pyz-Ru@MOFs exhibited excellent ECL performance. Using this 2D Pyz-Ru@MOFs as a sensing platform, a “signal-off” ECL immunosensor was constructed for CSFV analysis, which displayed high sensitivity and good selectivity for CSFV detection in the range of 10 fg mL−1 –10 ng mL−1 with a detection limit of 5.4 fg mL−1. In addition, the prepared immunosensor was successfully utilized for the satisfactory detection of CSFV in serum samples, which has potential application in biological analysis and clinical diagnosis. This proposed woke also provided a simple and feasible electrochemical synthesis strategy to construct 2D luminescent MOFs immobilized ECL luminophores, offering significant inspiration to develop highly efficient ECL materials at room temperature with ECL sensing applications.

A Rational Strategy to Assemble Porphyrins and Phthalocyanins into Crystalline Arrays: The SURMOF Approach

Realizing molecular “Designer Solids” by programmed assembly of building units taken from libraries is a very appealing objective. Recently, metal-organic frameworks (MOFs), or porous coordination polymers (PCPs) have attracted a huge interest in this context. Here, we will focus on MOF-based electrochemical, photoelectro-chemical, photovoltaic, and sensor devices built using porphyrin- and phthalocyanine-containing linkers. Internal interfaces in MOF heterostructures are also of interest with regard to photon-upconversion and the fabrication of diodes.Since the fabrication of reliable and reproducible contacts to MOF-materials represent a major challenge, we have developed a layer-by-layer (lbl) deposition method to produce well-defined, highly oriented and monolithic MOF thin films on appropriately functionalized substrates. The resulting films are referred to as SURMOFs [1,2] and have very appealing properties in particular with regard to optical applications [3]. The fabrication of hetero-multilayers is rather straightforward with this lbl method. In this talk, we will describe the principles of SURMOF fabrication as well as the results of systematic investigations of electrical and photophysical properties exhibited by empty MOFs and after loading their pores with functional guests. Band structure effects occurring in crystalline porphyrin arrays assembled using the SURMOF approach will also be discussed. [5] We will close with discussing further applications [4] realized by loading MOFs with nanoparticles or quantum dots and by creating molecular solids lacking inversion symmetry for second harmonic generation (SHG).[5]In the last part of the presentation we will point out that SURMOFs are very well suited for unattended experimentation approaches. Using robot systems controlled by machine learning (ML) algorithms allows to efficiently optimize thin film properties (orientation, crystallinity, roughness). We will discuss this point in particular in connection with the fabrication of SURMOF-based sensor systems.

(Invited) Engineering Molecular Solids and Monolithic Thin Films from Chromophoric Building Blocks: Model Systems and Integration into Devices

Functioning devices exploiting the properties of organic chromophores, e.g. in the context of photovoltaics, organic electronics, light-emitting devices, and photodetectors, often rely on the assembly of the molecules into appropriate solids and their interfacing to electrodes. In this context, recently the MOF-based approach [1] is receiving increasing attention. In this case, the organic chromophores (anthracene, pentacene, naphthalene-diimides, perylene-diimides, porphyrins, phthalocyanines, ...) are equipped with at least two coupling units so as to yield ditopic linkers suited for the coupling to metal- or metal-oxo nodes, thus yielding metal-organic frameworks (MOFs). Although the standard form of MOFs, powders, are not well suited for the integration of the arrayed chromophores into devices, in the past decade a number of methods able to yield high quality, monolithic MOF thin films deposited on a variety of substrates have been developed. Sophisticated fabrication methods, including layer-by-layer approaches yield films of impressive optical quality.[2]Optical absorption properties of condensed chromophores are often strongly affected by inter-molecular interactions. The periodic structure of MOFs provides the basis for a rational design of such assemblies, and e.g. J-aggregates have been first simulated and then realized experimentally.[3] In addition, band-structure effects like indirect band gaps can be realized in such periodic arrangements.[4] Finally, the implementation of chiral linkers allows to realize chiroptical phenomena, including the emission of circular polarized light and helicity-sensitive photodetectors.[5]Lbl architectures also allow the fabrication of heterostructures with built-in interfaces,[6] with interesting application e.g. in the context of photon up-conversion. A particularly attractive option is to exploit the porous nature of the MOFs in connection with the lbl method. An interesting example is the loading of C60 into the pores of SURMOFs and the subsequent integration into devices, e.g. in the context of photoconductivity [7] or organic diodes.[8] In the context of nonlinear optical properties, using sophisticated assembly strategies were recently used to fabricate non-centrosymmetric SURMOFs with built-in electric fields and large SHG activity.[9]In this presentation we well present selected successful examples of integrating organic chromophores into SURMOFs and the subsequent fabrication of functioning devices. We will in particular highlight the close interaction with theory. Such an advanced in-silico conquering of chemical spaces is mandatory, since the number of known MOFs (> 100.000) is so large that experimental trial-and-error approaches are highly inefficient.

Exploring the Impact of Successive Redox Events in Thin Films of Metal-Organic Frameworks: An Absorptiometric Approach.

Metal-organic frameworks (MOFs) featuring redox activity are highly appealing for electrocatalytic or charge accumulation applications. An important aspect in this field is the ability to address as many redox centers as possible in the material by an efficient diffusion of charges. Herein, we investigate for the first time the charge diffusion processes occurring upon two sequential one-electron reductions in an MOF thin film. Two pyrazolate-zinc(II)-based MOFs including highly electro-deficient perylene diimide (PDI) ligands were grown on conducting substrates, affording thin films with double n-type electrochromic properties as characterized by spectroelectrochemical analysis. In depth electrochemical and chronoabsorptiometric investigations were carried out to probe the charge diffusion in the MOF layers and highlighted significant differences in terms of diffusion kinetics and material stability between the first and second successive reduction of the redox-active PDI linkers. Our results show that MOFs based on multiredox centers are more sensitive to encumbrance-related issues than their monoredox analogues in the context of electrochemical applications, an observation that further underlines the fundamental aspect of careful pore dimensions toward efficient and fast ion diffusion.

Interfacial Engineering of Two-Dimensional Metal–Organic Framework Thin Films for Biomimetic Photoadaptative Sensors

Interfacial Engineering of Two-Dimensional Metal–Organic Framework Thin Films for Biomimetic Photoadaptative Sensors

Impact of Surface Functionalization and Deposition Method on Cu-BDC surMOF Formation, Morphology, Crystallinity, and Stability.

For direct integration into device architectures, surface-anchored metal-organic framework (surMOF) thin films are attractive systems for a wide variety of electronic, photonic, sensing, and gas storage applications. This research systematically investigates the effect of deposition method and surface functionalization on the film formation of a copper paddle-wheel-based surMOF. Solution-phase layer-by-layer (LBL) immersion and LBL spray deposition methods are employed to deposit copper benzene-1,4-dicarboxylate (Cu-BDC) on gold substrates functionalized with carboxyl- and hydroxyl-terminated alkanethiol self-assembled monolayers (SAMs). A difference in crystal orientation is observed by atomic force microscopy and X-ray diffractometry based on surface functionalization for films deposited by the LBL immersion method but not for spray-deposited films. Cu-BDC crystallites with a strong preferred orientation perpendicular to the substrate were observed for the films deposited by the LBL immersion method on carboxyl-terminated SAMs. These crystals could be removed upon testing adhesive properties, whereas all other Cu-BDC surMOF film structures demonstrated excellent adhesive properties. Additionally, film stability upon exposure to water or heat was investigated. Ellipsometric data provide insight into film formation elucidating 7 and 14 Å average thicknesses per deposition cycle for films deposited by the immersion method on 11-mercapto-1-undecanol (MUD) and 16-mercaptohexadecanoic acid (MHDA), respectively. In contrast, the films deposited by the spray method are thicker with the same average thickness per deposition cycle (21 Å) for both SAMs. While the spray method takes less time to grow thicker films, it produces similar crystallite structures, regardless of the surface functionalization. This research is fundamental to understanding the impact of deposition method and surface functionalization on surMOF film growth and to provide strategies for the preparation of high-quality surMOFs.

Porphyrin-Based MOF Thin Film on Transparent Conducting Oxide: Investigation of Growth, Porosity and Photoelectrochemical Properties.

Synthesizing metal-organic frameworks (MOFs) composites with a controlled morphology is an important requirement to access materials of desired patterning and composition. Since the last decade, MOF growth from sacrificial metal oxide layer is increasingly developed as it represents an efficient pathway to functionalize a large number of substrates. In this study, porphyrin-based Al-PMOF thin films were grown on conductive transparent oxide substrates from sacrificial layers of ALD-deposited alumina oxide. The control of the solvent composition and the number of atomic layer deposition (ALD) cycles allow us to tune the crystallinity, morphology and thickness of the produced thin films. Photophysical studies evidence that Al-PMOF thin films present light absorption and emission properties governed by the porphyrinic linker, without any quenching upon increasing the film thickness. Al-PMOF thin films obtained through this methodology present a remarkably high optical quality both in terms of transparency and coverage. The porosity of the samples is demonstrated by ellipsometry and used for Zn(II) insertion inside the MOF thin film. The multifunctional transparent, porous and luminescent thin film grown on fluorine-doped tin oxide (FTO) is used as an electrode capable of photoinduced charge separation upon simulated sunlight irradiation.

The Influence of Water in the Vapor‐Assisted Conversion Synthesis of UiO‐67 MOF Thin Films

AbstractWater is known to play an important role for the crystallization and stability of Zr‐based metal‐organic frameworks (MOFs). This work investigates its effect on the vapor‐assisted conversion (VAC) synthesis of UiO‐67 MOF thin films on Au‐coated Si substrates. We demonstrate the equilibration processes taking place during the VAC procedure, confirming the gradual equilibration of all solutions upon heating. The presence of water affects the vapor phase composition but does not significantly impact the acetic acid equilibration rate. However, the preparation of UiO‐67 thin films by VAC is highly sensitive to the water content in the reaction. Some water is required for the formation of the zirconium clusters, but excessive water in the reaction vial yields poorly crystalline materials. Atmospheric water that is taken up by the vapor source can be sufficient to reduce crystallinity dramatically. This complication can be partially overcome by increasing the amount of acetic acid in the vapor source.

Metal-Organic Framework Thin Films as Ideal Matrices for Azide Photolysis in Vacuum.

Studies on reactions in solutions are often hampered by solvent effects. In addition, detailed investigation on kinetics is limited to the small temperature regime where the solvent is liquid. Here, we report the in situ spectroscopic observation of UV-induced photochemical reactions of aryl azides within a crystalline matrix in vacuum. The matrices are formed by attaching the reactive moieties to ditopic linkers, which are then assembled to yield metal-organic frameworks (MOFs) and surface-mounted MOFs (SURMOFs). These porous, crystalline frameworks are then used as model systems to study azide-related chemical processes under ultrahigh vacuum (UHV) conditions, where solvent effects can be safely excluded and in a large temperature regime. Infrared reflection absorption spectroscopy (IRRAS) allowed us to monitor the photoreaction of azide in SURMOFs precisely. The in situ IRRAS data, in conjunction with XRD, MS, and XPS, reveal that illumination with UV light first leads to forming a nitrene intermediate. In the second step, an intramolecular rearrangement occurs, yielding an indoloindole derivative. These findings unveil a novel pathway for precisely studying azide-related chemical transformations. Reference experiments carried out for solvent-loaded SURMOFs reveal a huge diversity of other reaction schemes, thus highlighting the need for model systems studied under UHV conditions.

Proton conductive thin films of metal-organic framework for impedance detection of formic acid

The development of a highly efficient sensor capable of detecting formic acid is crucial for monitoring air quality and determining the leakage because of the strong corrosivity and pungency. In this work, we present the superiority of a proton conductive metal-organic framework (MOF) thin film as a sensing material for highly efficient detection of formic acid at room temperature. Specifically, MOF-801, a zirconium-based MOF, exhibits exceptional chemical stability and inherent proton conduction, along with a significant surface area and high porosity. Through the solvothermal synthetic method, highly uniform and densely packed thin films of MOF-801 are successfully fabricated on glass substrates. The resulting sensor, based on MOF-801 thin films, displays exceptional sensitivity, selectivity, and durability for detecting formic acid at room temperature, outperforming both other MOFs based sensors and the traditional metal-oxide-based sensors that operate at high temperatures.

Cerium-based metal–organic framework-conducting polymer nanocomposites for supercapacitors

Nanocomposites consisting of a cerium-based metal–organic framework (Ce-MOF-808) and a conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), are synthesized by performing the pulse electrodeposition of PEDOT within the Ce-MOF-808 thin films. Ratios between MOF and PEDOT in the composites are tunable by simply adjusting the charge density used for electropolymerization, and the crystallinity, morphology, and elemental distributions of the resulting nanocomposites are characterized. Electrochemical behaviors and capacitive performances of the pristine MOF, pristine PEDOT thin films, and composite thin films are investigated with the use of the neutral sodium sulfate aqueous electrolytes. The reversible electrochemical reactivity of the highly porous Ce-MOF-808 provides a pseudocapacitance, and the electronically conducting PEDOT can not only offer a remarkable double-layer capacitance but also facilitate the electronic conduction between the redox-active cerium sites present in the MOF. As a result, the composite can outperform both the pristine MOF and pristine electrodeposited PEDOT as the active materials for supercapacitors. Findings here suggest that the highly porous and redox-active cerium-based MOF thin films are capable to enhance the capacitive performances of the electrodeposited PEDOT thin films.

MOF-Assimilated High-Sensitive Organic Field-Effect Transistors for Rapid Detection of a Chemical Warfare Agent.

The selective and rapid detection of trace amounts of highly toxic chemical warfare agents has become imperative for efficiently using military and civilian defense. Metal-organic frameworks (MOFs) are a class of inorganic-organic hybrid porous material that could be potential next-generation toxic gas sensors. However, the growth of a MOF thin film for efficiently utilizing the material properties for fabricating electronic devices has been challenging. Herein, we report a new approach to efficiently integrate MOF as a receptor through diffusion-induced ingress into the grain boundaries of the pentacene semiconducting film in the place of the most adaptive chemical functionalization method for sensor fabrication. We used bilayer conducting channel-based organic field-effect transistors (OFETs) as a sensing platform comprising CPO-27-Ni as the sensing layer, coated on the pentacene layer, showed a strong response toward sensing of diethyl sulfide, which is one of the stimulants of bis (2-chloroethyl) sulfide, a highly toxic sulfur mustard (HD). Using OFET as a sensing platform, these sensors can be a potential candidate for trace amounts of sulfur mustard detection below 10 ppm in real time as wearable devices for onsite uses.

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.

Layer-by-Layer Grafting Dye on Chiral MOF Thin Films for Circularly Polarized Luminescence

Metal-organic frameworks with chiral feature (chirMOFs) are attracting great attention on circularly polarized luminescence (CPL). However, developing new efficient strategy to achieve or improve CPL properties is an urgent task. Herein, new chiral MOF thin films prepared by liquid-phase epitaxial layer by layer (lbl) growth method (SUR-chirMOF) are composed of D- or L-camphorate (D/Lcam) and aminopyrazine (Pr-NH2) by using liquid phase epitaxial layer by layer (lbl) method. The resulted Zn2(D/Lcam)2Pr-NH2 SURchirMOF shows strong chirality and luminescence but weak CPL emission at 390 nm. After lbl modifying a dye molecule FluoresceinIsothiocyanate (FITC), the chiroptical Zn2(D/Lcam)2Pr-NH-FITC SURchirMOFs with ~7 times CPL signal improvement and ~3 times glum value amplification are obtained. This work provides a new strategy to develop chiral MOF thin films for CPL improvement using lbl grafting approach.

In Situ Synchrotron X-ray Scattering Investigation of Cathodic ZIF-8 Deposition on Graphite Using 3D-Printed Cells

Electrochemical approaches provide unique means to fabricate thin films of metal-organic frameworks (MOFs). However, the kinetics of electrochemical MOF deposition has not been quantitatively investigated so far. In this study, we report the first in situ measurements of electrochemical MOF growth using transmission synchrotron X-ray scattering. Electrochemical cells based on poly(lactic acid) with two windows were fabricated using fused-deposition modeling. The resulting three-dimensional (3D)-printed cells, the surface of which was coated with paraffin wax to prevent solvent percolation through the polymer material, were used to monitor the cathodic growth of zeolitic imidazolate framework-8 (ZIF-8) on graphite in a methanol solution containing ZnCl2 and 2-methylimidazole (Hmim) at different cathodic potentials. The resulting time-resolved X-ray diffraction data showed a gradual increase in crystal size with negligible changes in crystal orientation during the cathodic ZIF-8 deposition. More importantly, the time-resolved data provided a means to quantitatively assess the kinetics of the cathodic ZIF-8 growth using the Gualtieri model, revealing that the cathodic potential and Hmim concentration affected crystal growth kinetics but not nucleation kinetics. These ZIF-8 samples exhibited changes in X-ray diffraction patterns after being washed with methanol and dried in air, indicating that in situ measurements are essential to investigate mechanisms behind MOF electrodeposition.

Epitaxial Single-Domain Cu-BTC Metal-Organic Framework Thin Films and Foils by Electrochemical Conversion of Cuprous Oxide.

Metal-organic frameworks (MOFs) are an important class of crystalline porous materials with extensive chemical and structural merits. However, the fabrication of MOF thin films oriented along all crystallographic axes to achieve well-aligned nanopores and nanochannels with uniform apertures remains a challenge. Here, we achieved highly crystalline single-domain MOF thin films with the [111] out-of-plane orientation by electrochemical conversion of cuprous oxide. Copper(II)-benzene-1,3,5-tricarboxylate, Cu3(BTC)2 (referred to as Cu-BTC), is a well-known metal-organic open framework material with a cubic crystal system. Epitaxial Cu-BTC(111) thin films were manufactured by electrochemical oxidation of Cu2O(111) films electrodeposited on single-crystal Au(111). The Cu-BTC(111) shows an in-plane antiparallel relationship with the precursor Cu2O(111) with a -0.91% coincidence site lattice mismatch. A plausible mechanism was proposed for the electrochemical conversion of Cu2O into Cu-BTC, indicating formation of intermediate CuO, growth of Cu-BTC islands, and termination with coalesce into a dense film with a limiting thickness of about 740 nm. The Faradaic efficiency for the electrochemical conversion was 63%. In addition, epitaxial Cu-BTC(111) foils were fabricated by epitaxial lift-off following the electrochemical etching of residual Cu2O underneath the Cu-BTC. It was also demonstrated that Cu-BTC(111) films with two in-plane domains and textured Cu-BTC(111) films can be achieved on a large scale using electrodeposited Au/Si and Au-coated glass as low-cost substrates.

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.