Haoran Li

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.

A series of d10 coordination polymers constructed with a rigid tripodal imidazole ligand and varied polycarboxylates: syntheses, structures and luminescence properties

Five novel Zn(II)/Cd(II) coordination polymers, [Zn2(tib)(L1)(μ2-OH)(HCOO)·2H2O]n (1), [Cd2(tib)2(L1)(NO3)2·2H2O·4DMF]n (2), [Cd2(tib)2(L2)(NO3)2·2H2O·4DMF]n (3), [Cd(tib)(L3)·H2O·2DMF]n (4) and [Cd3(tib)4(L4)·5/2NO3·1/2OH·3DMF]n (5) (tib = 1,3,5-tris(1-imidazolyl)benzene, H2L1 = terephthalic acid, H2L2 = isophthalic acid, H2L3 = 1,4-naphthalenedicarboxylic acid, H3L4 = (1α,3α,5α)-1,3,5-cyclohexanetricarboxylic acid, DMF = N,N-dimethylformamide), have been synthesized under solvothermal conditions. In compound 1, two-dimensional (2D) Zn-tib layers are pillared by L1 to afford a (3,5)-connected three-dimensional (3D) framework with topology (63)(69·8). Compound 2 displays a 2D + 2D → 2D interpenetrated bi-layer array based on a 2D (3,4) network. Compound 3 is characterized as an infinite one-dimensional (1D) chain structure, which is further extended into a 3D supramolecular architecture via weak π⋯π stacking interactions. Compound 4 possesses a 3D 2-fold interpenetrated architecture with the Schlafli symbol (42·65·83)(42·6). Compound 5 features a fascinating petal shaped (3,5)-connected network with a (42·6·84·103)3(42·6)3(83)2 topology which until now has never been documented. In this series of compounds, the diversity of the structures is tuned by the coordination geometries of the metal ions and the nature of the varied co-ligands. Furthermore, the luminescence properties of compounds 1–5 at room temperature have also been studied in detail.

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.

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.

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.

Doped polyaniline-hybridized tungsten oxide nanocrystals as hole injection layers for efficient organic light-emitting diodes

Solution-processed tungsten oxide nanocrystals (WO3 NCs) hybridized with a conductive polymer, polyaniline:poly(styrene sulfonate) (PANI:PSS), are introduced as a hole injection layer (HIL) in organic light-emitting diodes (OLEDs). These devices exhibited much higher current efficiency (CE) and power efficiency (PE) compared to regular devices without HILs and devices using pristine WO3 NCs as HILs. This enhanced device performance is mainly attributed to the facilitated hole injection due to the improvement in the energy level alignment at the interface between the ITO anode and the organic semiconductor layer. Besides, PANI:PSS can efficiently reduce surface defects and enhance the film-forming properties of WO3 NCs without affecting the device conductivity. These results suggest that PANI:PSS–WO3 could be a promising candidate for charge injection layers in optoelectronic devices.

CCDC 1527834: Experimental Crystal Structure Determination

Related Article: Haoran Li, Tianlu Sheng, Zhenzhen Xue, Xiaoquan Zhu, Shengmin Hu, Yuehong Wen, Ruibiao Fu, Chao Zhuo, Xintao Wu|2017|CrystEngComm|19|2106|doi:10.1039/C7CE00202E