Halogen-Bonded Organic Frameworks (XOFs) Based on N⋯Br+⋯N Bonds: Robust Organic Networks Constructed by Fragile Bonds.

Organic frameworks face a trade-off between the framework stability and the bonds dynamics, which necessitates the development of innovative linkages that enable stable frameworks without hindering efficient synthesis. While iodine(I)-based halogen-bonded organic frameworks (XOFs) have been developed, constructing XOFs based on bromine(I) is desirable yet challenging due to the high sensitivity of bromine(I) species. Here, we present the inaugural construction of stable bromine(I)-bridged two-dimensional (2D) halogen-bonded organic frameworks, XOF(Br)-TPy-BF4/OTf, based on sensitive [N…Br…N]+ halogen bonds. The formation of XOF(Br)-TPy-BF4/OTf was monitored by 1H NMR, XPS, IR, SEM, TEM, HR-TEM, SEAD. Their framework structures were established by the results from PXRD, theoretical simulations and SAXS. More importantly, XOF(Br) exhibited stable two-dimensional framework structures in various organic solvents and aqueous media, even over a wide pH range (pH 3-12), while the corresponding modelcompounds BrPy2BF4/OTf decomposed quickly even in the presence of minimal water. Furthermore, the influence of the counterions were investigated by replacing BF4 with OTf, which obviously improved the stability of XOF(Br). This characteristic enabled XOF(Br) to serve as efficient oxidizing reagents in aqueous environments, contrasting with the sensitivity of BrPy2BF4/OTf, which performed well only in organic media. This study opens new avenues for the development and application of multifunctional XOFs.

Construction of Halogen-Bonded Organic Frameworks (XOFs) as Novel Efficient Iodinating Agents.

The structural diversity and the various applications of organic frameworks have attracted much attention in recent years. Recently, halogen-bonded organic frameworks (XOFs) became a novel member of these materials, thereby facilitating the exploration of the interesting structures as well as functions. Here we present two types of [N···I+···N] connected XOFs (XOF-TPy and XOF-TPEB) with two tridentate ligands as building blocks. XOF-TPy and XOF-TPEB were characterized by 1H NMR, UV-vis, X-ray photoelectron spectroscopy (XPS), IR, SEM, and HR-TEM. Two-dimensional (2D) structural models were established based on powder X-ray diffraction (PXRD) data and theoretical simulations. Further experiment showed that these XOFs were excellent iodinating agents for the substituted arylboronic acids with either the electron-donating or electron-withdrawing groups upon heating without any catalyst. This research not only brings further understanding to the XOFs but also extends the applications of XOFs.

Halogen-Bonded Organic Framework (XOF) Based on Iodonium-Bridged N⋠⋠⋠I+ ⋠⋠⋠N Interactions: A Type of Diphase Periodic Organic Network.

Due to the fascinating structures and wide applications, porous materials with open frameworks have attracted more and more attentions. Herein, a novel two-dimensional (2D) halogen-bonded organic framework (XOF-TPPE) was successfully designed and fabricated by iodonium-bridged N⋅⋅⋅I+ ⋅⋅⋅N interactions between pyridyl groups and I+ for the first time. The formation of XOF-TPPE and its linear analogue was monitored by 1 H NMR, UV-Vis, X-ray photoelectron spectroscopy (XPS), IR, SEM, TEM, HRTEM and selected-area electron diffraction (SAED). The structural model of XOF-TPPE was established based on powder X-ray diffraction (PXRD) data and theoretical simulations. Significantly, synchrotron small-angle X-ray scattering (SAXS), DLS and UV-Vis spectroscopy experiments suggested that XOF-TPPE still maintains a stable 2D framework structure in solutions. This research opens up a novel avenue for the development of organic frameworks materials, and may bring new promising applications for the field of porous materials.

Pillararene-based AIEgens: research progress and appealing applications.

As a photophysical phenomenon, aggregation-induced emission (AIE) was proposed by Tang in 2001. Due to their excellent fluorescence emission performance, AIEgens and AIE-based fluorescence materials have shown great application potential in a wide range of science fields. Hence, exploring new AIEgens and construction of novel AIE materials are especially vital. In addition, as a new class of macrocyclic hosts, pillararenes have shown excellent performance in supramolecular chemistry. Interestingly, pillararenes also exhibited fairly bright application prospects in the AIE area: firstly, some research studies suggested that pillararenes could serve as a novel AIEgen with considerable fluorescence emission in the aggregated state; moreover, they could also participate in the construction of AIE materials and have potential application in various areas. In this review, we summarised the recent development of pillararene-based AIE materials from the following aspects: pillararenes as novel AIEgens, the TPE functionalized pillararene-based AIE materials, the pillararene-based AIE materials constructed by supramolecular assembly, and the functionalized pseudo-pillararene-based AIE materials. It is hoped that this feature article will attract increasing attention and pave a new way for the development and application of pillar[n]arene-based AIE materials in more fields.

Transparency and AIE tunable supramolecular polymer hydrogel acts as TEA-HCl vapor controlled smart optical material.

Stimuli-responsive optical materials attract lots of attention due to their broad applications. Herein, a novel smart stimuli-responsive supramolecular polymer was successfully constructed using a simple tripodal quaternary ammonium-based gelator (TH). The TH self-assembles into a supramolecular polymer hydrogel (TH-G) and shows aggregation-induced emission (AIE) properties. Interestingly, the transparency and fluorescence of the TH-G xerogel film (TH-GF) could be reversibly regulated by use of triethylamine (TEA) and hydrochloric acid (HCl) vapor. When alternately fumed with TEA and HCl vapor, the optical transmittance of the TH-GF was changed from 8.9% to 92.7%. Meanwhile, the fluorescence of the TH-G shows an "ON/OFF" switch. The reversible switching of the transparency and the fluorescence of the TH-GF is attributed to the assembly and disassembly of the supramolecular polymer TH-G. Based on these stimuli-response properties, the TH-GF could act as an optical material and shows potential applications as smart windows or fluorescent display material controlled by TEA and HCl vapor.

A novel AIE-based supramolecular polymer gel serves as an ultrasensitive detection and efficient separation material for multiple heavy metal ions.

Recently, ultrasensitive stimuli-responsive materials have received extensive attention due to their high sensitivity and wide applications. Herein, we report a novel approach to design ultrasensitive responsive materials by rationally introducing the aggregation-induced emission (AIE) effect into supramolecular polymer gels. According to this approach, by rationally introducing self-assembly moieties and a fluorophore, the obtained gelator DNS can act as an AIEgen; it showed strong AIE after aggregating into the supramolecular polymer gel GDNS. More interestingly, because the aggregation of DNS led to amplification of the detective signal, the AIE-based supramolecular polymer gel GDNS could ultrasensitively detect the heavy metal ions Hg2+, Cu2+, and Fe3+ by a signal amplification mechanism; the lowest detection limits reached 10-11 M. In addition, the xerogel of GDNS could adsorb and separate Hg2+, Cu2+, and Fe3+ from aqueous solution with favourable adsorption properties, and the adsorption rates ranged from 94.70% to 99.37%. Furthermore, the gel GDNS could act as a convenient test kit for Hg2+, Cu2+, and Fe3+ as well as a smart fluorescent display material.

A novel bis-component AIE smart gel with high selectivity and sensitivity to detect CN-, Fe3+ and H2PO4.

A novel bis-component AIE-gel TG was facilely constructed from two "easy-to-synthesize" tripodal gelators by a simple host-guest self-assembly process. Interestingly, the TG shows strong aggregation-induced emission (AIE) and could be used for highly efficient and sensitive detection and separation of ions (CN-, Fe3+ and H2PO4-). The LODs (limits of lowest detection) of TG for CN-, Fe3+ and H2PO4- are in the range of 4.93 × 10-9-7.80 × 10-8 M. Meanwhile, the xerogel of TG could adsorb and separate Fe3+ from aqueous solutions, and the adsorption rate is 96%. In addition, a thin film based on the TG could act as a convenient test kit for the detection of CN- and Fe3+. What is more, the TG-Fe film could not only be used as an erasable secure fluorescent display material, but also as a convenient reversible H2PO4- test kit.

Rationally introduce AIE into chemosensor: A novel and efficient way to achieving ultrasensitive multi-guest sensing.

Recently, ultrasensitive detection and multi-guest sensing have received extensive attention due to their high sensitivity and efficiency. Herein, we report a novel approach to achieve ultrasensitive detection of multi-analyte. This approach is concluded as "rationally introduce Aggregation-Induced Emission (AIE) into chemosensor". According to this approach, by rationally introducing self-assembly moiety, the obtained chemosensor DNS could serve as a novel AIEgen and show strong AIE in DMSO/H2O (water fraction 80%) binary solution. Interestingly, a simple fluorescent sensor array based on the DNS has been developed. This sensor array could selectively sense Fe3+, Al3+, H2PO4- and L-Arg in water solution. More importantly, this sensor array shows ultrasensitive detection for Fe3+, Al3+ and L-Arg. The LODs of the sensor array for Fe3+, Al3+ and L-Arg are in the range of 3.54×10-9M to 9.42×10-9M. Moreover, H2PO4- could realize the reversible detection of Fe3+ in the DMSO/H2O (water fraction 80%) solution. Meanwhile, DNS-based test papers and thin films were prepared, which could serve as test kits for convenient detection Fe3+, Al3+, and L-Arg in water. In addition, they could also act as efficient erasable fluorescent display materials.

Anion induced supramolecular polymerization: a novel approach for the ultrasensitive detection and separation of F.

A novel approach for the ultrasensitive detection and separation of F- has been successfully developed. F- could induce a tripodal naphthalene imide sensor (TNA) to result in supramolecular polymerization, leading to strong AIEE. The TNA could act as an excellent recyclable material for F- detection and separation.