Chao Zhuo

A Luminescent Metal–Organic Framework Thermometer with Intrinsic Dual Emission from Organic Lumophores

A new mixed-ligand metal-organic framework (MOF), ZnATZ-BTB, has been constructed as a luminescent ratiometric thermometer by making use of the intrinsic dual emission at cryogenic temperatures. Its twofold interpenetrated network promotes the Dexter energy transfer (DET) between the mixed organic lumophores. The temperature-dependent luminescent behavior arises from the thermal equilibrium between two separated excited states coupled by DET, which is confirmed by Boltzmann distribution fitting. The small excited-state energy gap allows ZnATZ-BTB to measure and visualize cryogenic temperatures (30-130 K) with significantly high relative sensitivity (up to 5.29% K(-1) at 30 K). Moreover, it is the first example of a ratiometric MOF thermometer the dual emitting sources of which are widely applicable mixed organic ligands, opening up new opportunities for designing such devices.

From Pair Quadruple- to Single-Stranded Helices to Lines in a Mixed Ligand System via Adjusting the N-Substituent of l-Glu

Utilizing the mixed-ligand strategy, a novel fourfold-interpenetrated 3D homochiral metal-organic framework (1) with rare pair quadruple-stranded helices was assembled from bpee (1,2-bis(4-pyridyl)ethylene) and NCG (N-carbamyl-l-glutamate). Changing the carbamyl substituent of NCG with benzoyl group (NBzG: N-benzoyl-l-glutamate), a non-interpenetrated 3D homochiral coordination polymer (2) composed of alternate right-handed and left-handed single helix was obtained. When p-tolylsulfonyl substituent was used instead, an interesting homochiral linear structure (3) was formed from mixed-ligand bpee and NTsG (N-p-tolylsulfonyl-l-glutamate), with all individual NTsG being lined up orderly. The steric hindrance of N-substituent of l-glu has a tremendous impact on the construction of these diverse frameworks. Complexes 1-3 display second harmonic generation (SHG) efficiencies, which are approximately 0.32, 0.45, and 0.55 times as much as that of KDP powder.

1D to 3D and Chiral to Noncentrosymmetric Metal–Organic Complexes Controlled by the Amount of DEF Solvent: Photoluminescent and NLO Properties

A mixture of 2D and 1D metal-organic complexes, [ZnL(H2O)2·G1·DEF·2H2O]n (1a: G1 = naphthalene-2,7-disulfonate; DEF = N,N-diethylformamide) and [ZnL(H2O)3·G1·DEF·2H2O]n (2), has been prepared from a hydrogenated Schiff base L and Zn(II) in a DEF-contained solvent system under mild conditions. The yields of 1a and 2 are equivalent; however, they can be tuned by varying the amount of DEF solvent. Increasing the use of DEF tends to form pure 1a, while decreasing it generates 2. Without DEF, another novel 3D four-connected CdSO4 (cds) framework [ZnL(H2O)2·G1·2H2O]n (3) composed of alternated right-handed and left-handed helical chains has been constructed. The amount of DEF solvent has a significant impact on the diverse coordination architectures of 1-3, which is rare in the preparation of metal-organic complexes. The photoluminescence of complexes 1-3 along with naphthalene-2,7-disulfonate has been investigated in the solid state. The luminescent emission of G1 was enhanced greatly after being confined into metal-organic networks. In addition, complexes 1-3 display second-harmonic generation efficiencies, which are approximately 0.58, 0.42, 0.32, and 0.52 times as much as that of potassium dihydrogen phosphate.

Strategies to construct homochiral metal–organic frameworks: ligands selection and practical techniques

The booming development of homochiral metal–organic frameworks (HMOFs) since the start of the 21st century has attracted considerable attention from the scientific community. With the features inherited from MOFs, HMOFs have great potential for application in gas storage, separation, sensing, catalysis, ferroelectric materials and nonlinear optics. Moreover, they show incomparable potential in enantioseparation and asymmetric catalysis, which are emergent technologies in modern chemical engineering. In this highlight, we summarize the classical ways to construct HMOFs based on the selection of ligands, as well as the practical techniques utilized. Moreover, the merits and demerits of each method are discussed along with the predictability of homochirality.

Syntheses, structures and luminescence properties of five coordination polymers based on designed 2,7-bis(4-benzoic acid)-N-(4-benzoic acid) carbazole

Herein we report five porous luminescent coordination polymers (CPs), namely, [Zn3(L27)2(DMA)6(H2O)4]n (TCZ-001), [Zn3(L27)2(DMA)6(CH3CH2OH)2]n (TCZ-002), [Zn3(L27)2(DMA)6(CH3OH)]n (TCZ-003), [Cd3(L27)2(DMA)6(H2O)2]n (TCZ-004), and [Cd9(L27)6DMA13(4,4′-BPY)2(OH)2(H2O)13.5]n (TCZ-005) [H3L27 = 2,7-bis(4-benzoic acid)-N-(4-benzoic acid) carbazole, DMA = N,N-dimethylacetamide, 4,4′-BPY = 4,4′-bipyridine, TCZ = “T”-shape carbazole-based polymers, L27 = fully deprotonated H3L273− ligand]. All of the five CPs were assembled from a novel luminescent carbazole-based ligand. X-ray crystallography showed that TCZ-001 is a 3-connected one-dimensional (1D) chain structure with a {42·6} topology. TCZ-002 possesses a 3,6-connected three-dimensional (3D) framework with a point symbol of {42·6}2{44·62·87·102}. TCZ-003 displays a 3,6-connected two-dimensional 2D network with a Schlafli symbol of {411·64}·{43}2, which is a new topology. TCZ-004 features a 3,6-connected 2D net with a {43}2·{46·66·83} topology. In TCZ-005, the structure can be classified into two groups: one of the two groups is a 3-connected 1D chain structure with a {42·6} topology, similar to TCZ-001; the other one possesses a 3,3,3,4-connected network with a Schlafli symbol of {42·63·8}{42·6}3. The structure of TCZ-005 could be described as an SP 1-periodic net (4,4)(0,2) in the 1D_2D.ttd database. TCZ-001, TCZ-003 and TCZ-004 show a remarkable response to the Ni2+ concentration in DMA, H2O or EtOH. Some of Zn2+ ions were replaced by Ni2+ ions and the rate of the transmetalation depended on the concentration of Ni2+ ions. Also, changing part of the metal node would transform the colour of emitted light. Additionally, the colour of the luminescence displays a linear correlation with the Ni2+ concentration range from 0.005 to 0.35 M (mol L−1). Besides selective sensing of Ni2+, TCZ-004 can also be utilized to detect Eu3+ in DMA solution. Thus, several potential sensory probe materials for Ni2+ and Eu3+ detection in DMA solution have been obtained.

Synthesis, structure, characterization, and multifunctional properties of a family of rare earth organic frameworks

A series of isomorphic 3D layered rare earth hydroxide (LREH) frameworks RE3(OH)7(1,5-NDS) (RE = Y (1), Gd (2), Er (3), Yb (4); 1,5-NDS = 1,5-naphthalenedisulfonate) has been synthesized under hydrothermal conditions. The crystal structures, thermal stabilities, photoluminescence, and magnetic properties of these compounds have been investigated. The results demonstrate that the compounds are highly stable even at 351 °C and emit strong purple fluorescence, whose colour can be tuned by the coordinated rare earth ions. Their magnetic susceptibilities have also been measured, leading the compounds to be promising multifunctional materials.

Confinement of an electron-capturing unit within an electron-donating framework for X-ray detection

A novel X-ray-induced photochromic metal–organic complex (cMOC-3) was constructed by confining an electron-capturing unit within the cavity of an electron-donating framework. Photochromic transformation from pale yellow to blue under X-ray irradiation was reversible, and recovered by thermal treatment. These phenomena can be attributed to metal-assisted ligand to ligand charge transfer (LLCT) between the electron-deficient unit and the electron-donating framework. Additionally, such a charge transfer process is responsible for switchable fluorescence regulated by X-ray irradiation with high photo-fatigue resistance. The X-ray-induced photochromism and fluorescence modulation opens a new avenue for developing convenient and quick-responsive smart optical materials for X-ray detection.

Intercalation of Varied Sulfonates into a Layered MOC: Confinement-Caused Tunable Luminescence and Novel Properties†

The pores/channels of porous 3D metal-organic frameworks (MOFs) have been widely applied to incorporate gas, solvent, or organic molecules. On the contrary, the utilization of the interlamellar void of layered metal-organic complexes (MOCs) remains underappreciated, although it is more flexible and available to accommodate molecules with different sizes. In this work, diverse sulfonates have been intercalated purposely into an identical layered MOC, which constructed various novel intercalation compounds possessing fluorescent, white-light emitting, photochromic, homochiral, or nonlinear optical (NLO) properties. With the help of single-crystal X-ray diffraction, their structures and the mutual interactions between the MOC host and the sulfonate guests were characterized. The properties of the guest molecules were tuned and meanwhile some new performances were generated after confining them into the interlayer region. Such a hybrid approach provides an efficient strategy to design and prepare multifunctional materials.

Homochiral Metal–Organic Frameworks with Tunable Nanoscale Channel Array and Their Enantioseparation Performance against Chiral Diols

Enantioseparation is an integral process in the pharmaceutical industry, considering the ever-increasing demand for chiral medicine products. As a new material, porous metal-organic frameworks (MOFs) have shown their potential application in this field because their structures are easy to adjust and control. Though chiral recognition between racemic substrates and frameworks has made preliminary progress, discussions of their size-matching effects are rare. Herein with the help of channel-tunable homochiral MOFs (HMOFs), diols of different sizes have been separated in good enantiomeric excess (ee%). In addition, the ee% reaches 67.4% for the first time for diols as large as 1,1,2-triphenyl-1,2-ethanediol, which turns out to be the most effective value so far.

Porous metal–organic frameworks based on 3,6-bis(4-benzoic acid)-N-(4-benzoic acid)carbazole for HPLC separation of small organic molecules

Porous metal–organic frameworks (MOFs) with an extensive range of pore sizes have great potential for efficient separation of small organic molecules. Herein, we report a new stable porous metal–organic framework {Cu3L2(4,4′-BPD)[NH(CH3)2]·7DMA·12H2O}n (YCZ-1), which was fabricated from a Cu-paddlewheel metal node and a new linker, namely 3,6-bis(4-benzoic acid)-N-(4-benzoic acid) carbazole (H3L). YCZ-1 possesses a doubly interpenetrated 3,5,6-connected three-dimensional (3D) framework with a Schlafli symbol of {512·83}·{52·8}4·{56·84}2, which is a new topology. The crystalline size of YCZ-1 could be controlled by adding different doses of dimethylamine, which would also be generated from DMA dissociated during the solvothermal reaction. Meanwhile, with excellent structural stability and outstanding surface area, the crystalline material YCZ-1 could be utilized as a stationary phase for high performance liquid chromatography (HPLC) separations during the separation of small organic molecules.