Encapsulation engineering of porous crystalline frameworks for delayed luminescence and circularly polarized luminescence.

Delayed luminescence (DF), including phosphorescence and thermally activated delayed fluorescence (TADF), and circularly polarized luminescence (CPL) exhibit common and broad application prospects in optoelectronic displays, biological imaging, and encryption. Thus, the combination of delayed luminescence and circularly polarized luminescence is attracting increasing attention. The encapsulation of guest emitters in various host matrices to form host-guest systems has been demonstrated to be an appealing strategy to further enhance and/or modulate their delayed luminescence and circularly polarized luminescence. Compared with conventional liquid crystals, polymers, and supramolecular matrices, porous crystalline frameworks (PCFs) including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), zeolites and hydrogen-bonded organic frameworks (HOFs) can not only overcome shortcomings such as flexibility and disorder but also achieve the ordered encapsulation of guests and long-term stability of chiral structures, providing new promising host platforms for the development of DF and CPL. In this review, we provide a comprehensive and critical summary of the recent progress in host-guest photochemistry via the encapsulation engineering of guest emitters in PCFs, particularly focusing on delayed luminescence and circularly polarized luminescence. Initially, the general principle of phosphorescence, TADF and CPL, the combination of DF and CPL, and energy transfer processes between host and guests are introduced. Subsequently, we comprehensively discuss the critical factors affecting the encapsulation engineering of guest emitters in PCFs, such as pore structures, the confinement effect, charge and energy transfer between the host and guest, conformational dynamics, and aggregation model of guest emitters. Thereafter, we summarize the effective methods for the preparation of host-guest systems, especially single-crystal-to-single-crystal (SC-SC) transformation and epitaxial growth, which are distinct from conventional methods based on amorphous materials. Then, the recent advancements in host-guest systems based on PCFs for delayed luminescence and circularly polarized luminescence are highlighted. Finally, we present our personal insights into the challenges and future opportunities in this promising field.

Triply Interlocked [2]catenanes: Rational Synthesis, Reversible Conversion Studies and Unprecedented Application in Photothermal Responsive Elastomer.

Triply interlocked [2]catenane complexes featuring two identical, mechanically interlocked units are extraordinarily rare chemical compounds, whose properties and applications remain open to detailed studies. Herein, we introduce the rational design of a new ligand precursor, L1, suitable for the synthesis of six triply interlocked [2]catenanes by coordination-driven self-assembly. The interlocked compounds can be reversibly converted into the corresponding simple triangular prism metallacage by addition of H2O or DMF solvents to their CH3OH solutions, thereby demonstrating the importance of π···π stacking and hydrogen bonding interactions in the formation of triply interlocked [2]catenanes. Moreover, extensive studies have been conducted to assess the remarkable photothermal conversion performance. Complex 6a, exhibiting outstanding photothermal conversion performance (conversion efficiency in solution : 31.82%), is used to prepare novel photoresponsive elastomer in combination with thermally activated liquid crystal elastomer. The resultant material displays robust response to near-infrared (NIR) laser and the capability of completely reforming the shape and reversible actuation, paving the way for the application of half-sandwich organometallic units in photo-responsive smart materials.

Realization of Single-Phase White-Light-Emitting Materials with Time-Evolution Ultralong Room-Temperature Phosphorescence by Coordination Assemblies.

Two Cd-based supramolecular coordination polymers, [Cd3(CzIP)3(DMF)2] (1) and [Cd2(CzIP)2(DMF)4] (2), were synthesized by using 5-(carbazol-9-yl) isophthalate (CzIP) as ligands. These two compounds exhibit multiple luminescence emissions; apart from fluorescence, time- and temperature-dependent ultralong phosphorescence (RTP) were also achieved under room conditions. Significantly, compound 1 has a long-lived afterglow of 0.93 s at 545 nm under ambient conditions. Compound 2 shows nearly pure white-light emission with CIE coordinates of (0.33, 0.33) via the dual emission of fluorescence and phosphorescence. It has come to our attention that it is the first example of a luminescent coordination polymer with single-phase white-light emission and color-evolution RTP. In addition, the long-lived RTP materials can be used in time-dependent anticounterfeiting and white-light-emitting diodes. Experimental and singlet and triplet state calculations indicate that both C-H···π interaction and inter- and intramolecular charge transfer interactions could be beneficial to the emission of ultralong RTP.

Tetraphenylethylene-Decorated Metal-Organic Frameworks as Energy-Transfer Platform for the Detection of Nitro-Antibiotics and White-Light Emission.

The highly porous luminescent metal-organic frameworks (MOFs) can act as fluorescent probes for the detection of nitro compounds and can also serve as containers and energy transfer platforms to construct the host-guest systems. Herein, two new three-dimensional MOFs with high porosity were prepared successfully by the electron-rich tetrakis(4-pyridylphenyl)ethylene (tppe) as ligands. Compound 1 shows the high sensitivity and selectivity toward nitro-antibiotics in an aqueous media, particularly showing the best detection efficiency for furazolidone (FZD) among the reported luminescent sensors. The highly efficient fluorescence quenching toward FZD may be attributed to the electron and energy transfer. Compound 2 has naphthalene-2,7-dicarboxylic acid (2,7-npd) and tppe as dual linkers, and the energy transfer between 2,7-npd and tppe leads to the emission band in a large scale. It is worth noting that the single-phased white-light materials can be obtained by the in situ encapsulation of different concentration of sulforhodamine 101 (SR101) into compound 2 matrix.

Selective Sorption of Light Hydrocarbons on a Family of Metal-Organic Frameworks with Different Imidazolate Pillars.

Four isostructural pillared-layer metal-organic frameworks (as 1-ims series) are successfully synthesized via the charge-balance approach, where trigonal [Zn2(CO2)3] cluster-based cationic layers [Zn2(NH2-BTB)](+) (NH2-H3BTB = 1,3,5-(3-benzoic acid) aniline) are connected by a series of 2-substituted imidazolates. The 1-ims supply a systematic platform to explore the adsorption of light hydrocarbons. Especially, 1-ims shows good adsorption selectivity of C3/C1 and C2/C1, and the selectivities of C3H8/CH4 are all over 100 at room temperature. These results demonstrate that introduction of functional group plays a key role on tuning the channel and pore size as well as improving the adsorption selectivity.

Structural transformation and hysteretic sorption of light hydrocarbons in a flexible Zn-pyrazole-adenine framework.

A three-dimensional metal-organic framework (MOF) was synthesized by combining 4-pyrazolecarboxylic acid and adenine. This MOF exhibits reversible flexibility and breathing adsorption behaviors in response to light hydrocarbons, with high capacity. The flexibility of the structural transitions was studied on the molecular scale by obtaining the crystal structures at 303, 353 and 373 K. The bridging nitrogen atoms of the pyrazolate rings act as a "kneecap" around the M⋅⋅⋅M axis, which causes the rotation of ligands around the M⋅⋅⋅M axis in response to external stimulus, thus giving rise to the deformation of the framework structure.

Size-Dependent Enantioselective Adsorption of Racemic Molecules through Homochiral Metal-Organic Frameworks Embedding Helicity.

Homochiral metal-organic frameworks (HMOFs) are efficient materials for enantioselective adsorption. However, the combination of size selectivity and enantioselectivity is still a major challenge in the field of HMOFs. Herein, two enantiomorphic HMOFs built from predesigned proline-derived ligands are presented. Both of them show multiple homochiral features: they contain four different helical chains and three types of helical channels. Due to the size effect of the helical channels, each HMOF can enantioselectively adsorb methyl lactate with high ee. The results reveal a new approach toward size-dependent enantioselective separation of racemic compounds by using HMOFs built from inexpensive proline derivatives.

Anionic metal-organic framework for adsorption and separation of light hydrocarbons.

The reaction of nickel(II) sulfate with 4,4',4"-s-triazine-2,4,6-triyltribenzoate in dimethyl sulfoxide afforded a hexanuclear nickel(II)-based anionic 2-fold interpenetrated metal-organic framework exhibiting the ability to adsorb and separate light hydrocarbons and canted antiferromagnetism.

Highly selective sorption of small hydrocarbons and photocatalytic properties of three metal-organic frameworks based on tris(4-(1H-imidazol-1-yl)phenyl)amine ligand.

By employing a tris(4-(1H-imidazol-1-yl)phenyl)amine (Tipa) ligand, three new metal-organic frameworks, [Zn2(Tipa)(4,4'-bpdc)1.5(H2O)(NO3)]·2(DMF)·H2O (1; 4,4'-bpdc = 4,4'-biphenyldicarboxylate, DMF = N,N-dimenthylformamide), [Cd(Tipa)Cl2]·2(DMF)·H2O (2), and [Co(Tipa)Cl2(H2O)]·DMF·H2O (3), have been synthesized solvothermally. Compound 1 features a three-dimensional (3D) pillared-layer structure with low band gap and interesting photocatalytic properties. Compound 2 is a 2-fold interpenetrating (3,6)-connected porous framework, and it shows highly selective adsorption of C2H2, CO2, and C2H4 over CH4. Compound 3 with honeycomb-like layers exhibits unusual 2D + 2D→ 3D polycatenation (2D = two-dimensional). The luminescent properties for these compounds were also investigated.

Homochiral metal-organic frameworks with enantiopure proline units for the catalytic synthesis of ß-lactams.

Two enantiopure organic ligands integrating flexible proline units and rigid isophthalate units have been rationally designed and employed for the construction of four homochiral porous metal-organic frameworks (MOFs), respectively. One pair of these MOFs is used as heterogeneous catalysts to construct ß-lactam derivatives by oxidative coupling reactions.

Hierarchical chiral MOFs with the induced chirality of AIE ligands exhibiting non-reciprocal CPL.

Two pairs of chiral MOFs with hierarchical chiral structures were constructed through assembly of achiral AIE-type multidentate linkers and chiral camphoric acid. Non-reciprocal circularly polarized luminescence (CPL) can be observed on the macroscopic due to the coexistence of optical anisotropic and chiroptical nature. This study provides a new perspective to recognize and construct chiral crystalline materials.

Porous ctn-type boron imidazolate framework for gas storage and separation.

BIFing it up: The assembly between triangular HB(mim)3 units and tetrahedral Zn centers (see graphic) leads to the formation of a ctn-type BIF material with high porosity for gas storage and separation (mim = 2-methylimidazolate).

Pillar-Layer Chiral MOFs as a Crystalline Platform for Circularly Polarized Luminescence and Single-Phase White-Light Emission.

The construction of circularly polarized luminescence (CPL) materials with high porosity and high rigidity is still challenging. Herein, we propose a chiral reticular chemistry strategy to prepare the homochiral porous metal-organic frameworks (MOFs) as CPL-active materials. Two pairs of enantiomeric MOFs are synthesized through the self-assembly of chiral D/L-cam (DL-camphorates) and achiral fluorescent ligand TPB (1,2,4,5-tetra(pyridin-4-yl)benzene). The glum values of Cd-CMOF-D and Cd-CMOF-L were up to 0.010 and 0.009; the high glum values could be compared to those of the partially pure multicomponent self-assembly systems obtained by the complicated process. We further trace the generation and transfer of the hierarchical chirality from chiral molecule to 3D framework, demonstrating that the CPL was dominated by the original molecular chirality rather than the global chirality of the hierarchical structure. Moreover, the single-phase white-light materials with nearly ideal CIE coordinates (0.33, 0.33) were constructed through the introduction of dye emitters into Zn-CMOF (Zn-based chiral MOF). This work provided not only an insightful view of the chirality transfer and disappearance mechanism but also an efficient method for the preparation of the highly porous CPL materials.

Multicolor-tunable room-temperature afterglow and circularly polarized luminescence in chirality-induced coordination assemblies.

Dynamic long-lived multicolor room temperature afterglow and circularly polarized luminescence (CPL) are promising for optoelectronic applications, but integration of these functions into a single-phase chiroptical material is still a difficult and meaningful challenge. Here, a nitrogen-doped benzimidazole molecule 1H-1,2,3-triazolopyridine (Trzpy) showing pure organic room-temperature phosphorescence (RTP) acted as a linker, and then, we propose a chirality-induced coordination assembly strategy to prepare homochiral crystal materials. Two homochiral coordination polymers DCF-10 and LCF-10 not only exhibit multicolor-tunable RTP, the color changed from green to orange under various excitation wavelengths, but also show remarkable excitation-dependent circularly polarized luminescence (CPL), and the dissymmetry factors of CPL in DCF-10 and LCF-10 are 1.8 × 10-3 and 2.4 × 10-3, respectively. Experimental and theoretical studies demonstrated that molecular atmospheres with different aggregation degrees give rise to multiple emission centers for the generation of multicolor-tunable emission. The multicolor-tunable photophysical properties endowed LCF-10 with a huge advantage for multi-level anti-counterfeiting. This work opens up new perspectives for the development and application of color-tunable RTP and CPL.

Neutral ligand TIPA-based two 2D metal-organic frameworks: ultrahigh selectivity of C2H2/CH4 and efficient sensing and sorption of Cr(vi ).

One neutral tripodal semi-rigidity ligand tri(4-imidazolylphenyl)amine (TIPA) with excellent hole-transfer nature, was selected as a linker to construct MOFs. Two two-dimensional (2D) microporous metal-organic frameworks (MOFs) were synthesized solvothermally: [Ni(TIPA)(COO-)2(H2O)]·2(DMF)2(H2O) (1) and [Cd(TIPA)2(ClO4-)2]·(DMF)3(H2O) (2). Compound 1 incorporated carboxylic groups into the channel and exhibited the high capacity of light hydrocarbons as well as the remarkable selectivity of C2H2/CH4. The value is in excess of 100 at room temperature, which is the highest value reported to date. Compound 2, as a cationic framework with high water stability, was not only applied as a sensor, displaying the ultrahigh sensitivity against Cr2O72- with a detection limit as low as 8 ppb, but also possessed excellent Cr(vi) sorption with good repeatability in aqueous solution. This study provides an efficient strategy to design cationic MOFs for the selective separation of light hydrocarbons and the sensing and trapping of toxic chromate for the purification of water.

Dual-Emission SG7@MOF Sensor via SC-SC Transformation: Enhancing the Formation of Excimer Emission and the Range and Sensitivity of Detection.

In this study, a water stable metal-organic framework FIR-53 is applied as a single-crystal container for anion exchange. The exceptional chemical stability and low crystallographic symmetry of FIR-53 makes it possible to determine anionic guests. Through ion exchange and single-crystal to single-crystal (SC-SC) transformation, 8-hydroxypyrene-1,3,6-trisulfonate (SG7, solvent green 7, ion form as SG73-) is introduced into the pores of FIR-53 to obtain SG7@FIR-53. Because of the spatial confinement and partition effect, SG7@FIR-53 shows the bright exciter emission of SG7 ions. Interestingly, the composite SG7@FIR-53 exhibits a sensitive fluorescence quenching response against Cr2O72- and MnO4- in aqueous solution. Especially, the detection limit toward MnO4- is as low as 0.12 ppb, which is the smallest value to date. Moreover, the prepared SG7@FIR-53 film also displays a broad response to nitro explosives in vapor/aqueous phase. Compared with the results of FIR-53, the range and sensitivity were greatly improved.

Spatial confinement of a cationic MOF: a SC-SC approach for high capacity Cr(vi)-oxyanion capture in aqueous solution.

A water-stable cationic MOF could be used as a single crystal container to capture Cr(vi)-oxyanions via ion exchange with high capacity and selectivity. It is the first report that demonstrates that CrO42- ions could be traced and confirmed via a single-crystal to single-crystal (SC-SC) pattern.

Engineering design toward exploring the functional group substitution in 1D channels of Zn-organic frameworks upon nitro explosives and antibiotics detection.

Three isostructural metal-organic frameworks denoted as Zn(L)(aip)·(H2O) (1), Zn(L)(ip)·(DMF)(H2O)1.5 (2), and Zn(L)(HBTC)·(H2O)2 (3) with functional groups -NH2, -H and -COOH, respectively, decorated on the 1D channels have been rationally designed with the purpose of exploring the influence of electron transfer from organic ligands in the 1D channels on the sensing of nitro explosives and antibiotics. These three compounds exhibit strong fluorescence in water, and they can be applied to detect the presence of explosives or antibiotics by means of fluorescence quenching in aqueous solution, whereas in terms of special explosives or antibiotics at the same concentration, 3 demonstrates a more superior quenching efficiency than 1 and 2. More importantly, it has been found that the difference in the sensing performances of these compounds is closely related to the interaction between the functional groups and guest molecules via electron and energy transfer from MOFs to explosives and antibiotics.

Synthesis of Hierarchical Sisal-Like V2O5 with Exposed Stable {001} Facets as Long Life Cathode Materials for Advanced Lithium-Ion Batteries.

Vanadium pentoxide (V2O5) is considered a promising cathode material for advanced lithium-ion batteries owing to its high specific capacity and low cost. However, the application of V2O5-based electrodes has been hindered because of their inferior conductivity, cycling stability, and power performance. Herein, hierarchical sisal-like V2O5 microstructures consisting of primary one-dimensional (1D) nanobelts with [001] facets orientation growth and rich oxygen vacancies are synthesized through a facile hydrothermal process using polyoxyethylene-20-cetyl-ether as the surface control agent, followed by calcination. The primary 1D nanobelt shortens the transfer path of electrons and ions, and the stable {001} facets could reduce the side reaction at the interface of electrode/electrolyte, simultaneously. Moreover, the formation of low valence state vanadium would generate the oxygen vacancies to facilitate lithium-ion diffusion. As a result, the sisal-like V2O5 manifests excellent electrochemical performances, including high specific capacity (297 mA h g-1 at a current of 0.1 C) and robust cycling performance (capacity fading 0.06% per cycle). This work develops a controllable method to craft the hierarchical sisal-like V2O5 microstructures with excellent high rate and long-term cyclic stability.

A stable zinc-4-carboxypyrazole framework with high uptake and selectivity of light hydrocarbons.

A special organic ligand, 4-carboxypyrazole (4-cpz), is chosen to synthesize a highly stable metal-organic framework (MOF) for selective sorption of light hydrocarbons. The new MOF, (H(3)O)[Zn(3)(OH)(4-cpz)3]·2(DEF)·H(2)O (FIR-51, DEF = N,N-diethylformamide), was synthesized solvothermally and shows unusual chemical stability. This compound exhibits high storage capacity for light hydrocarbons and high selectivity for C3 and C2 over methane at 273 and 294 K.