Recent Advances in the Z/E Isomers of Tetraphenylethene Derivatives: Stereoselective Synthesis,AIE Mechanism,Photophysical Properties,and Application as Chemical Probes

Focused research on the Z/E isomers of tetraphenylethene (TPE) derivatives is scarce in comparison with the thousands of luminogens with AIE properties (AIEgens) that have been synthesized based on the TPE moiety. The similar chemical and physical properties of the Z/E isomers make them difficult to separate by using conventional chromatographic techniques. However, they can be isolated by introducing polar groups and the pure isomers exhibit very different photophysical properties, mechanochromism, and host–guest coordination, as well as assisting in deciphering the AIE mechanism. In this Minireview, we present an overview of the disagreement regarding the AIE mechanism between the restriction of intramolecular vibration and photoinduced Z/E isomerization. Then, we discuss the development of (Z)‐/(E)‐TPE derivatives, their use in host–guest detection, and their mechanoluminescence properties, with a focus on their photophysical characteristics. Finally, we explore the stereoselective synthesis of pure (Z)‐/(E)‐TPE derivatives.     

A Maleimide‐functionalized Tetraphenylethene for Measuring and Imaging Unfolded Proteins in Cells

Collapse of the protein homeostasis (proteostasis) can lead to accumulation and aggregation of unfolded proteins, which has been found to associate with a number of disease conditions including neurodegenerative diseases, diabetes and inflammation. Here we report a maleimide‐functionalized tetraphenylethene (TPE)‐derivatized fluorescent dye, TPE‐NMI, which shows fluorescence turn‐on property upon reacting with unfolded proteins in vitro and in live cells under proteostatic stress conditions. The level of unfolded proteins can be measured by flow cytometry and visualized with confocal microscopy.     

Synthesis of Luminescent Covalent–Organic Polymers for Detecting Nitroaromatic Explosives and Small Organic Molecules

Three porous luminescent covalent‐‐organic polymers (COPs) have been synthesized through self‐polycondensation of the monomers of tris(4‐bromophenyl)amine, 1,3,5‐tris(4‐bromophenyl)benzene, and 2,4,6‐tris‐(4‐bromo‐phenyl)‐[1,3,5]triazine by using Ni‐catalyzed Yamamoto reaction. All the COP materials possess not only high Brunauer–Emmett–Teller (BET) specific surface area of about 2000 m² g⁻¹, high hydrothermal stability, but also graphene‐like layer texture. Interestingly, COP‐3 and COP‐4 show very fast responses and high sensitivity to the nitroaromatic explosives, and also high selectivity for tracing picric acid (PA) and 2,4,6‐trinitrotoluene (TNT) at low concentration (<1 ppm). In short, the COPs may be a new kind of material for detecting explosives and small organic molecules.     

A Fluorescent Zirconium‐Based Metal‐Organic Framework for Selective Detection of Nitro Explosives and Metal Ions

In this work, a new porous Zr‐based metal‐organic framework (MOF ) with a large Brunner‐Emmet‐Teller (BET ) surface area was prepared by the solvothermal method using 4,4’‐(naphthalene‐1,4‐diyl)dibenzoic acid (NDDA ) as the organic ligand, and the luminescent detection performance was studied systematically. The experiments combing with computations indicate that the as‐synthesized material can sensitively and selectively detect nitro explosives and metal ions, especially for 2,4,6‐trinitrophenol (TNP ) and Fe³⁺, due to the possible electron transfer from inorganic moieties to organic moieties with naphthalene part. Interestingly, owing to its high porosity and large surface area, this Zr‐MOF showed quick luminescent response time (in 1 min) for TNP and Fe³⁺. The results obtained may provide useful information for the design of MOFs with the large permanent porosity in sensing applications for large molecules in the future.     

荧蒽修饰的四苯基乙烯衍生物:分子合成、聚集增强荧光特性及其对苦味酸的高灵敏度检测

由于聚集体和固态发光量子效率高等优点,因此聚集诱导发光（AIE）材料成为光电功能材料研究领域的热点,拓展AIE分子体系始终是这一领域中的关键和基础的科学问题.通过Suzuki-Miyaura偶联这一条件较为温和的反应,将AIE生色团四苯基乙烯（TPE）与荧蒽直接共轭键接,制备得到单荧蒽和双荧蒽修饰的TPE衍生物TPE-FA与TPE-DFA,它们具有聚集增强荧光（AEE）行为,聚集体发射峰值波长分别在477和494 nm,固体薄膜的绝对荧光量子产率高达74.1%和40.4%.它们可以高灵敏地检测苦味酸,荧光猝灭常数大,检出限低于1 μg·g^-1.这两种AEE分子可望用于其它多硝基取代的芳香类吸电子分子的检测.     

AIE Polymers: Synthesis,Properties, and Biological Applications

Aggregation‐caused quenching (ACQ) is a general phenomenon that is faced by traditional fluorescent polymers. Aggregation‐induced emission (AIE) is exactly opposite to ACQ. AIE molecules are almost nonemissive in their molecularly dissolved state, but they can be induced to show high fluorescence in the aggregated or solid state. Incorporation of AIE phenomenon into polymer design has yielded various polymers with AIE characteristics. In this review, the recent progress of AIE polymers for biological applications is summarized.

     

Synthesis,photoluminescence, and electroluminescence characterization of double tetraphenylethene‐tethered BODIPY luminogens

Three double tetraphenylethene (TPE)‐tethered 4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indance (BODIPY) fluorophores, 35TPEBODP , 88TPEBODP , and 26TPEBODP , have been synthesized and characterized. The green 35TPEBODP with deep red fluorescence shows serious thermal decomposition in the purification process of sublimation, which prohibits its test for an organic light‐emitting diode (OLED) fabricated by the vacuum–thermal evaporation process. The tethered TPE is attached to BODIPY at three different positions, resulting in different photoluminescence (emission wavelength and quantum yield) and electroluminescence (EL). Different from TPE‐tethered BODIPY fluorophores reported in literature, none of the BODIPY fluorophores studied here exhibits aggregation‐induced emission (AIE), aggregation‐induced enhanced emission (AIEE), or twisted intramolecular charge transfer (TICT) characteristics. Although solution (10^?5 M THF) photoluminescence quantum yields (?s) are relatively high at 78%, 68%, and 86% for 35TPEBODP , 88TPEBODP , and 26TPEBODP , respectively, which are all higher than 41% of PhBODP (a non‐TPE‐tethered BODIPY), the ? is significantly decreased to 1–6% in 5 wt% dopant polystyrene thin film or as a solid powder, except for 13% of 26TPEBODP . Therefore, due to the low ? of dopant thin film or solid powder, either dopant or nondopant OLEDs exhibit inferior external quantum efficiency (EQE) and intensity of EL. The best OLED in this study is the 26TPEBODP device, and its EQE reaches 1.3%, and the highest EL intensity is approximately 1,600 cd/m².     

Graphenes Prepared by Hummers,Staudenmaier and Hofmann Methods for Analysis of TNT‐Based Nitroaromatic Explosives in Seawater

The detection of TNT and related nitroaromatic compounds in seawater is of great interest. Electrochemical techniques can be applied for detection purposes since nitroaromatic compounds contain easily reducible nitro groups. In this study, we investigate the performance of thermally reduced graphenes prepared by three different oxidative methods: Hummers, Staudenmaier and Hofmann methods with consequent thermal exfoliation. The Hofmann method‐based graphene was found to exhibit the highest sensitivity in detecting TNT electrochemically. Extended study on the detection of TNT in seawater using the graphene material provided significant improvements in the detection sensitivity. These findings will have profound impacts on the detection of nitroaromatic explosives in seawater.     

Thermally Stable 3,6‐Dinitropyrazolo[4,3‐c]pyrazole‐based Energetic Materials

3,6‐Dinitropyrazolo[4,3‐c]pyrazole was prepared using an efficient modified process. With selected cations, ten nitrogen‐rich energetic salts and three metal salts were synthesized in high yield based on the 3,6‐dinitropyrazolo[4,3‐c]pyrazolate anion. These compounds were fully characterized by IR and multinuclear NMR spectroscopies, as well as elemental analyses. The structures of the neutral compounds 4 and its salt 16 were confirmed by single‐crystal X‐ray diffraction showing extensive hydrogen‐bonding interactions. The neutral pyrazole precursor and its salts are remarkably thermally stable. Based on the calculated heats of formation and measured densities, detonation pressures (22.5–35.4 GPa) and velocities (7948–9005 m s^?1) were determined, and they compare favorably with those of TNT and RDX. Their impact and friction sensitivities range from 12 to >40 J and 80 to 360 N, respectively. These properties make them competitive as insensitive and thermally stable high‐energy density materials.     

Graphene Nanoribbons from Tetraphenylethene‐Based Polymeric Precursor: Chemical Synthesis and Application in Thin‐Film Field‐Effect Transistor

Graphene nanoribbons (GNRs) with a non‐zero bandgap are regarded as a promising candidate for the fabrication of electronic devices. In this study, large‐scale solution synthesis of narrow GNRs was firstly achieved by the intramolecular cyclodehydrogenation of kinked tetraphenylethene (TPE) polymer precursors prepared by A₂B₂‐type Suzuki‐Miyaura polymerization. After the cyclization reaction, the nanoribbons have a better conjugation than the twisted polymer precursor, resulting in obvious red shift in UV/vis absorption and photoluminescence (PL) spectra. The efficient formation of conjugated nanoribbons was also investigated by Raman, FTIR spectroscopy, and microscopic studies. Furthermore, such structurally well‐defined GNRs have been successfully developed for top‐gated field‐effect transistor (FET) by directly solution processing. The AFM images show that the prepared‐GNRs thin films form crystalline fibrillar intercalating networks, which can effectively facilitate the charge transport. These FET devices with ion‐gel gate dielectrics exhibit low‐voltage operation (<5 V) with excellent mobility up to 0.41 cm²·V^?1·s^?1 and an on‐off ratio of 3×10⁴, thus opening up new opportunities for flexible GNRs‐based electronic devices.     

Chromo‐Fluorogenic Detection of Nitroaromatic Explosives by Using Silica Mesoporous Supports Gated with Tetrathiafulvalene Derivatives

Three new hybrid gated mesoporous materials ( SN₃‐1 , SNH₂‐2 , and SN₃‐3 ) loaded with the dye [Ru(bipy)₃]²⁺ (bipy=bipyridine) and capped with different tetrathiafulvalene (TTF) derivatives (having different sizes and shapes and incorporating different numbers of sulfur atoms) have been prepared. The materials SN₃‐1 and SN₃‐3 are functionalized on their external surfaces with the TTF derivatives 1 and 3 , respectively, which were attached by employing the “click” chemistry reaction, whereas SNH₂‐2 incorporates the TTF derivative 2 , which was anchored to the solid through an amidation reaction. The final gated materials have been characterized by standard techniques. Suspensions of these solids in acetonitrile showed “zero release”, most likely because of the formation of dense TTF networks around the pore outlets. The release of the entrapped [Ru(bipy)₃]²⁺ dye from SN₃‐1 , SNH₂‐2 , and SN₃‐3 was studied in the presence of selected explosives (Tetryl, TNT, TNB, DNT, RDX, PETN, PA, and TATP). SNH₂‐2 showed a fairly selective response to Tetryl, whereas for SN₃‐1 and SN₃‐3 dye release was found to occur with Tetryl, TNT, and TNB. The uncapping process in the three materials can be ascribed to the formation of charge‐transfer complexes between the electron‐donating TTF units and the electron‐accepting nitroaromatic explosives. Finally, solids SNH₂‐2 and SN₃‐1 have been tested for Tetryl detection in soil with good results, pointing toward a possible use of these or similar hybrid capped materials as probes for the selective chromo‐fluorogenic detection of nitroaromatic explosives.     

AIE Fluorescent Gelators with Thermo‐, Mechano‐, and Vapochromic Properties

A series of aggregation‐induced emission (AIE) fluorescent gelators (TPE‐C_n‐Chol) were synthesized by attaching tetraphenylethylene (TPE) to cholesterol through an alkyl chain. The properties of the gel, nano‐/microaggregate, and condensed phases were studied carefully. TPE‐C_n‐Chol molecules form AIE fluorescent gels in acetone and in DMF. Their fluorescence can be reversibly switched between the “on” and “off” states by a gel–sol phase transition upon thermal treatment. The AIE properties of aggregated nano‐/microstructures in acetone/water mixtures with different water fractions were studied by using fluorescence spectrometry and scanning electron microscopy (SEM). In different acetone/water mixtures, the TPE‐C_n‐Chol molecules formed different nano‐/microaggregates, such as rodlike crystallites and spherical nanoparticles that showed different fluorescence colors. Finally, the condensed phase behavior of TPE‐C_n‐Chol was studied by using polarizing microscopy (POM), differential scanning calorimetry (DSC), fluorescence spectrometry, fluorescence optical microscopy, and wide‐angle X ray scattering (WAXS). The clover‐shaped TPE unit introduced into the rodlike cholesterol mesogen inhibits not only the formation of a liquid‐crystal phase but also recrystallization upon cooling from the isotropic liquid phase. Very interestingly, TPE‐C_n‐Chol molecules in the condensed state change their fluorescence color under external stimuli, such as melting, grinding, and solvent fuming. The phase transition is the origin of these thermo‐, mechano‐, and vapochromic properties. These findings offer a simple and interesting platform for the creation of multistimuli‐responsive fluorescent sensors.     

A High Contrast Tri‐state Fluorescent Switch: Properties and Applications

A high contrast tri‐state fluorescent switch (FSPTPE) with both emission color change and on/off switching is achieved in a single molecular system by fusing the aggregation‐induced emissive tetraphenylethene (TPE) with a molecular switch of spiropyran (SP). In contrast to most of the reported solid‐state fluorescent switches, FSPTPE only exists in the amorphous phase in the ring‐closed form owing to its highly asymmetric molecular geometry and weak intermolecular interactions, which leads to its grinding‐inert stable cyan emission in the solid state. Such an amorphous phase facilitates the fast response of FSPTPE to acidic gases and induces the structural transition from the ring‐closed form to ring‐open form, accompanied with the “Off” state of the fluorescence. The structural transition leads to a planar molecular conformation and high dipole moment, which further results in strong intermolecular interactions and good crystallinity, so when the acid is added together with a solvent, both the ring‐opening reaction and re‐crystallization can be triggered to result in an orange emissive state. The reversible control between any two of the three states (cyan/orange/dark) can be achieved with acid/base or mechanical force/solvent treatment. Because of the stable initial state and high color contrast (Δλ=120 nm for cyan/orange switch, dark state Φ_F<0.01 %), the fluorescent switch is very promising for applications such as displays, chemical or mechanical sensing, and anti‐counterfeiting.     

iCVD Cyclic Polysiloxane and Polysilazane as Nanoscale Thin‐Film Electrolyte: Synthesis and Properties

A group of crosslinked cyclic siloxane (Si O) and silazane (Si N) polymers are synthesized via solvent‐free initiated chemical vapor deposition (iCVD). Notably, this is the first report of cyclic polysilazanes synthesized via the gas‐phase iCVD method. The deposited nanoscale thin films are thermally stable and chemically inert. By iCVD, they can uniformly and conformally cover nonplanar surfaces having complex geometry. Although polysiloxanes are traditionally utilized as dielectric materials and insulators, our research shows these cyclic organosilicon polymers can conduct lithium ions (Li⁺) at room temperature. The conformal coating and the room temperature ionic conductivity make these cyclic organosilicon polymers attractive for use as thin‐film electrolytes in solid‐state batteries. Also, their synthesis process and properties have been systemically studied and discussed.

     

A Fluorescent Sensor for Highly Selective Detection of Nitroaromatic Explosives Based on a 2D,Extremely Stable,Metal–Organic Framework

A 2D, extremely stable, metal–organic framework (MOF), NENU‐503 , was successfully constructed. It displays highly selective and recyclable properties in detection of nitroaromatic explosives as a fluorescent sensor. This is the first MOF that can distinguish between nitroaromatic molecules with different numbers of ?NO₂ groups.     

Preparation and Properties of the Emulsions of the Polysiloxane Material Modified with Tertiary Amino Side Chain

A series of the polysiloxane materials modified with tertiary amino groups were synthesized. FTIR, ¹H NMR were used to characterize the polysiloxane structure. The emulsions of the modified polysiloxanes are prepared. Some surface properties of the polysiloxane materials with tertiary amino groups as resins were discussed. The results show that the polysiloxane materials modified with tertiary amino side chains had good flexibility and the repellency to water. With increasing the amino value of the polysiloxanes, the flexibility of the fabrics treated with the emulsion was improved. After the samples treated with the polysiloxanes, the thermal yellowing of the polysiloxane had emerged. The whiteness of fabrics treated with the polysiloxane decreased. The K/S of the yellow fabrics treated with the modified polysiloxanes had not obvious change, the K/S of the red and blue fabrics treated with the modified polysiloxanes slightly decreased. The shapes of the reflectance spectra curves of the dyed fabrics treated without and with the modified polysiloxanes had not noticeable change.     

Synthesis and Duplex‐Stabilizing Properties of Fluorinated N‐Methanocarbathymidine Analogues Locked in the C3′‐endo Conformation

The efficient synthesis, antiviral activity, and duplex‐stabilizing properties of both isomers of the 2′‐fluoro analogue of Northern methanocarbathymidine (N‐MCT), 2 and 3 , are reported. We show that 2′‐F incorporation on the N‐MCT scaffold has a strong stabilizing effect on duplex thermal stability.     

Simple Biosensor with High Selectivity and Sensitivity: Thiol‐Specific Biomolecular Probing and Intracellular Imaging by AIE Fluorogen on a TLC Plate through a Thiol–Ene Click Mechanism

A handy, specific, sensitive bioprobe has been developed. Tetraphenylethene (TPE) was functionalized by a maleimide (MI) group, giving a TPE‐MI adduct that was nonemissive in both solution and the solid state. It was readily transformed into a fluorogen showing an aggregation‐induced emission (AIE) property by the click addition of thiol to its MI pendant. The click reaction and the AIE effect enabled TPE‐MI to function as a thiol‐specific bioprobe in the solid state. Thus, the spot of TPE‐MI on a TLC plate became emissive when it had been exposed to L ‐cysteine, an amino acid containing a thiol group, but remained nonemissive when exposed to other amino acids that lack free thiol units. The thiol‐activated emission was rapid and strong, readily detected by the naked eye at an analyte concentration as low as approximately 1 ppb, thanks to the “lighting up” nature of the bioprobing process. Similarly, the emission of TPE‐MI was turned on only by the proteins containing free thiol units, such as glutathione. Clear fluorescence images were taken when living cells were stained by using TPE‐MI as a visualization agent, affording a facile fluorescent maker for mapping the distribution of thiol species in cellular systems.