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

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

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.

Experimental and Theoretical Studies on Effects of Structural Modification of Tin Nanoclusters for Third-Order Nonlinear Optical Properties.

Tin oxide based materials have attracted much attention as new sources for nonlinear optical (NLO) devices, while the electronic mechanism behind the structure and nonlinearity is still unclear. In this work, by precisely controlling different functionalization ligands, here a series of binuclear [(nBuSn)2(TEOA)2L2] (L = monocarboxylic acid ligand) complexes have been synthesized and characterized; we also adopted a new method to make the metal clusters and PMMA blend together for NLO testing. Importantly, the electronic structure, static third-order NLO properties, sum over states (SOS) have been studied by both experimental and density function theory (DFT) analysis. The effects for general NLO polarizability under various conditions, including different substitutions ligands and replacement of the metal cores, have been further investigated. The results indicate the static second hyperpolarizabilities (γ) is inversely proportional to the band gap decreases. Notably, the theory predicts that the third-order nonlinear coefficient will double through the synergistic effects of pull-push groups. The hole-electron analysis of the main excited states indicates the simultaneous introduction of pull-push electron groups into the system cause the excitation of the valence layer from LE to LLCT, which also leads to significant increase in the γ value of complex 13. This work demonstrates that an efficient adjustment for the intensity of NLO polarizability can be achieved by regulating the substitutions and the material structures, providing a new potential for the application of tin-oxo clusters in the field of nonlinear optics.

Combining a Titanium-Organic Cage and a Hydrogen-Bonded Organic Cage for Highly Effective Third-Order Nonlinear Optics.

Many metal-organic cages (MOCs) and a few hydrogen-bonded organic cages (HOCs) have been investigated, but little is reported about cooperative self-assembly of MOCs and HOCs. Herein, we describe an unprecedented MOC&HOC co-crystal composed of tetrahedral Ti4 L6 (L=embonate) cages and in-situ-generated [(NH3 )4 (TIPA)4 ] (TIPA=tris(4-(1H-1,2,4-triazol-1-yl)phenyl)amine) cages. Chiral transfer is observed from the enantiopure Ti4 L6 cage to enantiopure [(NH3 )4 (TIPA)4 ] cage. Two homochiral supramolecular frameworks with opposite handedness (PTC-235(Δ) and PTC-235(Λ)) are formed. Such MOC&HOC co-crystal features high stability in water and other solvents, affording single-crystal-to-single-crystal transformation to trap CH3 CN molecules and identify disordered NH4 + cations. A tablet pressing method is developed to test the third-order nonlinear optical property of KBr-based PTC-235 thin film. Such a thin film exhibits an excellent optical limiting effect.

Designable Al32 -Oxo Clusters with Hydrotalcite-like Structures: Snapshots of Boundary Hydrolysis and Optical Limiting.

The hydrolysis of earth-abundant AlIII has implications in mineral mimicry, geochemistry and environmental chemistry. Third-order nonlinear optical (NLO) materials are important in modern chemistry due to their extensive optical applications. The assembly of AlIII ions with π-conjugated carboxylate ligands is carried out and the hydrolysis and NLO properties of the resultant material are studied. A series of Al32 -oxo clusters with hydrotalcite-like cores and π-conjugated shells are isolated. X-ray diffraction revealed boundary hydrolysis occurs at the equatorially unsaturated coordination sites of AlIII ions. Charge distribution analysis and DFT calculations support the proposed boundary substitution. The Al32 -oxo clusters possess a significant reverse saturable absorption (RSA) response with a minimal normalized transmittance up to 29 %, indicating they are suitable candidates for optical limiting (OL) materials. This work elucidates the hydrolysis of AlIII and provides insight into layered materials that also have strong boundary activity at the edges or corners.

Self-Assembly of a Ti4(embonate)6 Cage toward Silver.

Herein we report a variety of supramolecular architectures that are self-assembled by the highly charged anionic Ti4L6 (L = embonate) cages and noble-metal Ag+ ions in the presence of the different ligands, including six Ti4L6-Ag(PPh3) cages in whose structures the Ti4L6 cage catches various in situ formed [Ag(PPh3)]+ moieties by a coordination bond and one cocrystal superstructure of a Ti4L6 cage with an in situ generated [Ag2(Ph2P(CH2)5PPh2)3]2+ cage via supramolecular interactions. In addition, the third-order nonlinear-optical properties of these compounds are investigated in detail.

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.

MOF-Templated Synthesis of Ultrasmall Photoluminescent Carbon-Nanodot Arrays for Optical Applications.

Arrays of ultrasmall and uniform carbon nanodots (CDs) are of pronounced interest for applications in optical devices. Herein, we describe a low-temperature calcination approach with rather inexpensive reactants. After glucose molecules had been loaded into the pores of metal-organic frameworks (MOFs), well-defined CD arrays were produced by heating to 200 °C. The size and spacing of the CDs could be controlled by the choice of templating MOF: HKUST-1, ZIF-8, or MIL-101. The sizes of the obtained CDs were approximately 1.5, 2.0, and 3.2 nm, which are close to the corresponding MOF pores sizes. The CD arrays exhibited interesting photophysical properties, including photoluminescence with tunable emission and pronounced nonlinear optical (NLO) effects. The NLO properties of the obtained CD arrays were significantly different from those of a CD suspension, thus indicating the existence of collective phenomena.

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.

Heterometallic Al6Zn12 nano-plate with π-conjugated ligand: synthesis and nonlinear absorption properties.

Presented herein is the synthesis, structure, and optical properties of the aluminum(III)-zinc(II) heterometallic compound AlOC-57. This compound was found to form a large unit cell (approximately sixteen thousand atoms) and a three-shell nano-plate structure. Based on the Z-scan patterns, the third-order nonlinear optical response of the heterometallic nano-plate was mainly attributed to its nonlinear absorption (reverse saturable absorption).

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.

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

The design and development of the supercapacitors containing metal oxides and carbon materials is very important for energy-storage devices in laboratory and industry. In this study, we report a helical carbon tube material derived from epitaxial Cu-MOF coating on textile by calcination treatment. The electrochemical performance obtained from the cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and cyclic stability measurements indicates that such a hybrid carbon material with a unique structure has a very high areal capacitance of 1812 mF cm-2 at a current density of 1 mA cm-2, and the material also has a good recyclability of 90% after 2000 cycles. This study combines the advantages of MOF- and cotton textile-derived carbon materials, and this study can serve as a guidance to improve the capacitance performance of supercapacitors.

Single molecule magnetic behaviour in lanthanide naphthalenesulfonate complexes.

The use of 2-naphthalenesulfonate (NAS) ligand in lanthanide chemistry afforded a family of isostructural mononuclear lanthanide complexes with the formula [Ln(NAS)2(H2O)6](NAS)·3H2O [Ln = Tb (1), Dy (2), Er (3), Yb (4)]. Crystallographic studies determined a square antiprismatic geometry (D4d) for the Ln centre and crystallization in an unprecedented chiral space group. The latter was further confirmed by the observation of Cotton effects in single crystal circular dichroism (CD) spectra. Static and dynamic magnetic measurements identified weak intermolecular dipolar interactions in 2, and such effects can be waived by dilution, which was noted by the detection of zero-field single molecule magnet (SMM) behaviour and hysteresis loop in a magnetically diluted sample (5). Compounds 2-4 exhibit SMM behaviours with energy barriers of 53, 32, and 45 K, respectively. To the best of our knowledge, these complexes are the first examples of pure 4f sulfonate-based SMMs.

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.