Construction of deep-blue AIE luminogens with TPE and oxadiazole units

In this paper, two AIE-active luminogens (Oxa-pTPE and Oxa-mTPE) constructed from tetraphenylethene and oxadiazole units were successfully synthesized and their thermal, optical and electronic properties were investigated. By linking TPE to the oxadiazole core through meta-or para-position, the intramolecular conjugation is effectively controlled. Thanks to the intelligent molecular design and specific AIE feature, when fabricated as emissive layers in non-doped OLEDs, they exhibit blue or deep-blue emission with CIE coordinates of (0.17, 0.23) and (0.15, 0.12), and good efficiencies with ηC, max and ηP, max up to 1.52 cd A-1 and 0.84 Im W-1 , shedding some light on the construction of deep-blue AIE fluorophores.     

Synthesis,aggregation-induced emission and thermally activated delayed fluorescence properties of two new compounds based on phenylethene,carbazole and 9,9′,10,10′-tetraoxidethianthrene

In the text, two luminescent materials ECPPTT and ECDPTT, have been designed and synthesized by integrating tetraphenyl/triphenyl-ethene(TPE/TrPE), carbazole group and thianthrene-9,9,10,10-tetraoxide unit. ECPPTT and ECDPTT possess obvious AIE and TADF capabilities, and show good thermal stability in their thin film of 240 °C and 262 °C, respectively. Non-doped organic light emitting diodes(OLED) using ECPPTT and ECDPTT as emission layer are prepared and exhibit blue-green and green emission color with peaks at 494, 517 nm, respectively. The non-doped OLED based on ECPPTT provides good peak EL efficiencies of 3.437 cdA^-1 and 10090cdm^-2; while non-doped OLED fabricated with ECDPTT affords a maximum current efficiency and a maximum luminance of 2.478 cdA^-1 and 7561cdm^-2. These results have demonstrated the feasibility of combing AIE and TADF units to design new molecules.     

Coordination-Induced Emission from Tetraphenylethylene Units and Their Applications

Thanks to the potential of aggregation-induced emission (AIE) phenomena, improved stabilities, and the good selectivity and sensitivity of the chemical responses exhibited by the products, coordination-driven self-assembly with tetraphenylethylene (TPE) units has recently received much attention and has been widely investigated for application in chemical sensors, cell imaging agents, light-harvesting systems, and others. Several reviews have emerged on the topics of AIE chemistry and aggregation-induced emission luminogen (AIEgen)-based supramolecular assembles, however, there is still a distinct lack of full overviews of emission enhancement from the viewpoint of metal-coordination effects. Thus, this minireview offers recent advances that have been made in the design and application of TPE-based metallacycles, metallacages, metal-organic frameworks (MOFs) and coordination polymers (CPs).     

A fluorescent supramolecular crosslinked polymer gel formed by crown ether based host-guest interactions and aggregation induced emission

Based on the combination of B21C7/dialkylammonium salt host-guest interactions and tetraphenylethylene(TPE)-based aggregation-induced emission(AIE) effect, a fluorescent supramolecular crosslinked polymer gel was successfully prepared. Compared with the solution of TPE-containing small molecules, this gel exhibited remarkable fluorescence enhancement due to the AIE effect of TPE units. The "gelation induced fluorescence emission" phenomenon can be explained by the hindered intramolecular rotation of phenyl rings of TPE. Because of the reversibility and stimuli-responsiveness of the B21C7/dialkylammonium salt host-guest interactions, the transition between the fluorescent supramolecular crosslinked polymer gel and the disassembled sol with very weak fluorescence can be realized by adding p H and thermal stimuli. This novel material contributes to the development of supramolecular chemistry, polymer science and fluorescent materials and offers a new method to construct functional supramolecular materials.     

Investigating the effects of side chain length on the AIE properties of water-soluble TPE derivatives

The emissive properties of fluorophores in aggregated state are important for the development of bio-sensors or bio-imaging reagents. So three water-soluble TPE derivatives with different lengths of side chains have been synthesized and we investigated the effects of side chains on aggregation-induced emission (AIE) properties in the aggregated states. The results indicate that side chains on the fluorophores play a pivotal role in their emission in aggregated state mediated by heparin or solid state, because the coplanarity of these TPE derivatives was affected by side chains. The rates of radiative decay k_f and non-radiative decay k_nr have been obtained through the quantum yields and lifetime, and a larger k_f and smaller k_nr were present for compound TPE-C4N, suggesting that the aggregated TPE-C4N should posses the most remarkable fluorescent property.     

Synthesis of selenium bridged metallacycles via oxidative addition of diaryl diselenide across Re-Re bond: Novel one-pot reaction approach

One-pot synthesis of novel M₂E₂L₂ type metallacycles [L(CO)₃Re(μ-SeR)₂Re(CO)₃L] (1-5) was accomplished by oxidative addition of diaryl diselenide to low-valent transition metal carbonyl with monodentate pyridine ligands. In metallacycles 1-5, where L = pyridine ligand, R = C₆H₅, CH₂C₆H₅, the pyridyl groups bonded to metal centres invariably adopted cis conformation due to π-π interaction whereas, in compounds 1a and 2a, the pyridyl ligands were oriented in trans conformation. When bulky phenyl groups are introduced at para position of pyridyl rings, as in case of metallacycle 3, the steric hindrance disrupts the soft interaction and resulted into the expansion of space in between two phenylpyridyl groups and created a void. The Metallacycles 1-5 have been characterised by elemental analysis, NMR, IR, absorption and emission spectroscopic techniques. Molecular structures of 1, 1a, 2, 2a, 3 and 4 were determined by single crystal X-ray diffraction analysis and the structural studies of 1, 2, 3 and 4 revealed that the pyridyl groups attached to the metal centres exhibited cis conformation, while 1a, 2a displayed trans conformation.     

A new fluorescent sensor for the detection of pyrophosphate based on a tetraphenylethylene moiety

We have developed a new fluorescent sensor 1-2Zn based on a tetraphenylethylene (TPE) moiety for the detection of PPi. This TPE-based chemosensor showed ‘turn-on’ fluorescence emission according to the concentration of PPi. The fluorescence enhancement upon binding of PPi to 1-2Zn resulted from the restriction of intramolecular rotation of phenyl rings in 1-2Zn.     

Constructing a Nonfluorescent Conformation of AIEgen: A Tetraphenylethene Embedded in the Calix[4]arene's Skeleton

Two novel 1,1‐diphenylmethylidene decorated calix[4]arenes, ( Calix‐DPE(OCH₃)₄ and Calix‐DPE(OH)₄ ), were designed and prepared. The tetraphenylethene (TPE) unit is embedded in the calix[4]arenes skeleton, so the conformation of tetraphenylethene unit is significantly affected by the conformation of calix[4]arene. Unlike the Calix‐DPE(OCH₃)₄ , the Calix‐DPE(OH)₄ does not show the aggregation‐induced emission (AIE) phenomena in solution or the crystal state because of the presence of intramolecular hydrogen bonding, which leads to a cone conformation for the calix[4]arene skeleton in which the embedded phenyl rings of the TPE have to take an almost perpendicular configuration to the C=C bond. This result provides direct evidence that the maximal cross‐chromophore π‐conjugation within the tetraphenylethene is one of the prerequisites of switching on its AIE. This offers the possibility of switching the emission of TPE by conformation changes.     

Fluorescent Bioprobes: Structural Matching in the Docking Processes of Aggregation‐Induced Emission Fluorogens on DNA Surfaces

Whereas most conventional DNA probes are flat disklike aromatic molecules, we explored the possibility of developing quadruplex sensors with nonplanar conformations, in particular, the propeller‐shaped tetraphenylethene (TPE) salts with aggregation‐induced emission (AIE) characteristics. 1,1,2,2‐Tetrakis[4‐(2‐triethylammonioethoxy)phenyl]ethene tetrabromide (TPE‐ 1 ) was found to show a specific affinity to a particular quadruplex structure formed by a human telomeric DNA strand in the presence of K⁺ ions, as indicated by the enhanced and bathochromically shifted emission of the AIE fluorogen. Steady‐state and time‐resolved spectral analyses revealed that the specific binding stems from a structural matching between the AIE fluorogen and the DNA strand in the folding process. Computational modeling suggests that the AIE molecule docks on the grooves of the quadruplex surface with the aid of electrostatic attraction. The binding preference of TPE‐ 1 enables it to serve as a bioprobe for direct monitoring of cation‐driven conformational transitions between the quadruplexes of various conformations, a job unachievable by the traditional G‐quadruplex biosensors. Methyl thiazolyl tetrazolium (MTT) assays reveal that TPE‐ 1 is cytocompatible, posing no toxicity to living cells.     

A functional conjugated hyperbranched polymer derived from tetraphenylethene and oxadiazole moieties: Synthesis by one-pot “a4+b2+c2” polymerization and applicaion as explosive chemosensor and pled

A new conjugated hyperbranched polymer (hb-TFO) containing tetraphenylethylene (TPE) units, a famous aggregation-induced emission (AIE) active group, as the core, was synthesized successfully with modest yield via one-pot Suzuki polymerization reaction. Thanks to the introduction of TPE moieties, hb-TFO exhibited aggregation-enhanced emission (AEE) property, and could work as explosive chemosensor with high sensitivity. The polymeric light-emitting diode (PLED) device was fabricated to investigate its electroluminescent property, and hb-TFO demonstrated a maximum luminance efficiency of 0.22 cd/A and a maximum brightness of 545 cd/m² at 15.9 V.     

Opposite ESIPT characteristic of two AIE-active isomers with different linkage sites

In this work, we report two isomers composed of 1-phenyl-1H-phenanthro[9,10-d]imidazole (PI), hydroxyl and tetraphenylethylene (TPE), abbreviated as m-PITPE and p-PITPE. It is found that they exhibit similar aggregation-induced emission (AIE) behavior but totally different excited-state intramolecular proton transfer (ESIPT) characteristic, as a result of the different linkage sites of PI on TPE moiety. Theoretical calculations and their different experimental responses to F^? demonstrate that only the para-linkage isomer displays ESIPT. In m-PITPE with meta-linkage, the electron cloud distribution only locates at the TPE part in the singlet excited (S₁) states, which results in the localized excited state without ESIPT characteristic.     

Novel Functional Conjugative Hyperbranched Polymers with Aggregation‐Induced Emission: Synthesis Through One‐Pot “A2+B4” Polymerization and Application as Explosive Chemsensors and PLEDs

With the aim to develop new tetraphenylethylene (TPE)‐based conjugated hyperbranched polymer, TPE units, one famous aggregation‐induced emission (AIE) active group, are utilized to construct hyperbranched polymers with three other aromatic blocks, through an “A₂+B₄” approach by using one‐pot Suzuki polycondensation reaction. These three hyperbranched polymers exhibit interesting AIEE behavior and act as explosive chemsensors with high sensitivity both in the nanoparticles and solid states. This is the first report of the AIE activity of the TPE‐based conjugated hyperbranched polymers. Their corresponding PLED devices also demonstrate good performance.     

A Strategy for Dramatically Enhancing the Selectivity of Molecules Showing Aggregation‐Induced Emission towards Biomacromolecules with the Aid of Graphene Oxide

By intelligently utilizing the different interacting strengths between different moieties according to the displacement method, general biosensors with aggregation‐induced emission (AIE) characteristics for biomacromolecules without selectivity were converted to excellent, highly selective probes for one specific biomacromolecule with the aid of graphene oxide (GO) in an aqueous medium. Importantly, thanks to the different interactions between the AIE molecule and biomacromolecules, just by simply changing the AIE molecule the sensing system could detect different types of biomacromolecules, thereby providing a new approach to the development of AIE‐based sensors with high selectivity and sensitivity. More specifically, the complex of A₂HPS?HCl—a derivative of hexaphenylsilone (HPS) functionalized by two amino (A₂) groups (N(CH₂CH₃)₃)—and GO only gives an “off–on” response to DNA, with a detection limit of 2.3 μg mL^?1 toward DNA‐CT (calf thymus); interestingly, the complex of TPE‐N₂C₄ (1,2‐bis{4‐[4‐(N,N,N‐triethylammonium)butoxy]phenyl}‐1,2‐diphenylethene dibromide) and GO could only detect the presence of bovine serum albumin (BSA), whereas other biomacromolecules, including DNA, RNA, and even other proteins have very little influence.     

Efficient enhancement of fluorescence emission via TPE functionalized cationic pillar[5]arene-based host–guest recognition-mediated supramolecular self-assembly

A tetraphenylethene (TPE) functionalized cationic pillar[5]arene (CWP5-TPE) was successfully synthesized, and the intramolecular rotation of the TPE motif was restricted via cationic pillar[5]arene-based host–guest recognition-mediated supramolecular self-assembly in water, resulting in the efficient enhancement of fluorescence emission based on the aggregation induced emission (AIE) mechanism. CWP5-TPE self-assembled into nanoribbons while the host–guest inclusion complex formed into supramolecular amphiphile nanoparticles in water.     

Crystal structure of 1,3-diphenyladamantane and trans-1,4-diphenylcyclohexane: torsion angles about C-Ph bonds in α,ω-diphenyl(alicyclic hydrocarbon)

The orientation of the two phenyl rings in α,ω-diphenylalkanes with rigid carbon skeletons is investigated through characterization of the crystal and molecular structures of 1,3-diphenyladamantane (1) and trans-1,4-diphenylcyclohexane (2). The two phenyl rings in 1 have different conformations about the C-Ph bonds, with torsion angles between the phenyl ring and the C1-C2-C3 plane of 0.65 and 71.7°. A hydrogen atom at the meta-position of one of the phenyl rings contact intermolecularly with a tertiary hydrogen atom at C5 of adamantane within the sum of van der Waals radii. Due to the helical conformation, the short CH?HC contacts (2.231 Å) construct supramolecular triple helical strands. In contrast to 1, the phenyl rings in 2 have identical configurations, with equatorial position and bisected conformation as expected from density functional calculations. The molecular packing of 2 exhibits a herringbone pattern of (aromatic)C-H?π contacts.     

Aggregation‐Induced Emission Characteristics of o‐Carborane‐Functionalized Tetraphenylethylene Luminogens: The Influence of Carborane Cages on Photoluminescence

Tetraphenylethylene (TPE)–carborane hybrids are constructed, and the impact of carborane substituents on the aggregation‐induced emission (AIE) characteristics of TPE‐cores has been investigated. When altering the 2‐R‐group on the carborane unit with ‐H, ‐CH₃ or phenyl group, the luminescent quantum yield of the corresponding TPE derivatives can be manipulated from 0.18 to 0.63 in the solid state. The emission color exhibits an obvious 100 nm shift (from blue to yellow).     

Hexaphenylbenzene‐Based, π‐Conjugated Snowflake‐Shaped Luminophores: Tunable Aggregation‐Induced Emission Effect and Piezofluorochromism

In this work, two rigid, multiple tetraphenylethene (TPE)‐substituted, π‐conjugated, snowflake‐shaped luminophores BT and BPT were facilely synthesized by using a 6‐fold Suzuki coupling reaction. These molecules are constructed based on the nonplanar structure of propeller‐shaped hexaphenylbenzene (HPB) or benzene as core groups and TPE as end groups. As a result, they reserve the intrinsic aggregation‐induced emission (AIE) property of the TPE moiety. Meanwhile, both fluorescence quantum yield and piezochromic behavior in the solid state can be tuned or switched by inserting the phenyl bridges through changing the twisting conformation. The more extended structure BPT showed a much stronger AIE effect and higher Φ_F,f in the solid state in comparison with that of BT. Furthermore, an excellent optical waveguide application of these molecules was achieved. However, the revisable piezofluorochromic behavior has only appeared when BT was ground using a pestle and treated with solvent.     

Zinc (II) and AIEgens: The “Clip Approach” for a Novel Fluorophore Family. A Review

Aggregation-induced emission (AIE) compounds display a photophysical phenomenon in which the aggregate state exhibits stronger emission than the isolated units. The common term of “AIEgens” was coined to describe compounds undergoing the AIE effect. Due to the recent interest in AIEgens, the search for novel hybrid organic–inorganic compounds with unique luminescence properties in the aggregate phase is a relevant goal. In this perspective, the abundant, inexpensive, and nontoxic d¹⁰ zinc cation offers unique opportunities for building AIE active fluorophores, sensing probes, and bioimaging tools. Considering the novelty of the topic, relevant examples collected in the last 5 years (2016–2021) through scientific production can be considered fully representative of the state-of-the-art. Starting from the simple phenomenological approach and considering different typological and chemical units and structures, we focused on zinc-based AIEgens offering synthetic novelty, research completeness, and relevant applications. A special section was devoted to Zn(II)-based AIEgens for living cell imaging as the novel technological frontier in biology and medicine.     

Self-assembly of emissive metallocycles with tetraphenylethylene,BODIPY and terpyridine in one system

ABSTRACT

Tetraphenylethylene (TPE) related (supra)molecules have been intensively investigated due to their aggregation-induced emission (AIE) effect based on the restriction of intramolecular rotation (RIR). Meanwhile, boron-dipyrromethene (BODIPY) tends to emit intense fluorescence with high quantum yields. Herein, we combined TPE, BODIPY and terpyridine (TPY) into one system to study the emissive behaviour of organic building block as well as a self-assembled metallo-supramolecule. The TPY and BODIPY substituents with bulky sizes provide strong hindrance to restrict the rotation of the phenyl groups on TPE, leading to enhancement of emissive properties in both solution and aggregation states. Furthermore, the BODIPY-TPE-TPY ligand (L) was assembled with Zn (II) through coordination-driven self-assembly to form a cyclic dimer (D) with typical AIE characteristics.     

Designing a highly stable coordination-driven metallacycle for imaging-guided photodynamic cancer theranostics

Coordination-driven self-assembly features good predictability and directionality in the construction of discrete metallacycles and metallacages with well-defined sizes and shapes, but their medicinal application has been limited by their low stability and solubility. Herein, we have designed and synthesized a highly stable coordination-driven metallacycle with desired functionality derived from a perylene-diimide ligand via a spontaneous deprotonation self-assembly process. Brilliant chemical stability and singlet oxygen production ability of this emissive octanuclear organopalladium macrocycle make it a good candidate toward biological studies. After cellular uptake by endocytosis, the metallacycle exhibits potent fluorescence cell imaging properties and cancer photodynamic therapeutic ability through enhancing ROS production, with high biocompatibility and safety. This study not only provides a rational design strategy for highly stable luminescent organopalladium metallacycles, but also sheds light on their application in imaging-guided photodynamic cancer therapy.

A highly-luminescent metallacycle with chemical stability and singlet oxygen production ability were obtained by a spontaneous deprotonation self-assembly process, which exhibits application potential in imaging-guided photodynamic cancer therapy.