Conjugated Coordination Nanosheets with Molecular Rotors for Pseudocapacitors: Nanoarchitectonics and Enhanced Performance.

High-level pseudocapacitive materials require incorporations of significant redox regions into conductive and penetrable skeletons to enable the creation of devices capable of delivering high power for extended periods. Coordination nanosheets (CNs) are appealing materials for their high natural electrical conductivities, huge explicit surface regions, and semi-one-layered adjusted pore clusters. Thus, rational design of ligands and topological networks with desired electronic structure is required for the advancement in this field. Herein, we report three novel conjugated CNs (RV-10-M, M=Zn, Ni, and Co), by utilizing the full conjugation of the terpyridine-attached flexible tetraphenylethylene (TPE) units as the molecular rotors at the center. We prepare binder-free transparent nanosheets supported on Ni-foam with outstanding pseudocapacitive properties via a hydrothermal route followed by facile exfoliation. Among three CNs, the high surface area of RV-10-Co facilitates fast transport of ions and electrons and could achieve a high specific capacity of 670.8 C/g (1677 F/g) at 1 A/g current density. Besides, the corresponding flexible RV-10-Co possesses a maximum energy density of 37.26 Wh kg-1 at a power density of 171 W kg-1 and 70 % capacitance retention even after 1000 cycles.

Biomimetic Hydrogen-Bonded G ⋠C ⋠G ⋠C Quadruplex within a Tetraphenylethene-Based Octacationic Spirobicycle in Water.

In biological systems, nucleotide quadruplexes (such as G-quadruplexes) in DNA and RNA that are held together by multiple hydrogen bonds play a crucial functional role. The biomimetic formation of these hydrogen-bonded quadruplexes captured by artificial systems in water poses a significant challenge but can offer valuable insights into these complex functional structures. Herein, we report the formation of biomimetic hydrogen-bonded G ⋅ C ⋅ G ⋅ C quadruplex captured by a tetraphenylethene (TPE) based octacationic spirobicycle (1). The spirobicyclic compound possesses a three-dimensional (3D) crossing dual-cavity structure, which enables the encapsulation of four d(GpC) dinucleotide molecules, thereby realizing 1 : 4 host-guest complexation in water. The X-ray structure reveals that four d(GpC) molecules further form a two-layer G ⋅ C ⋅ G ⋅ C quadruplex with Watson-Crick hydrogen bonds, which are stabilized within the dual hydrophobic cavities of 1 through the cooperative non-covalent interactions of hydrogen bonds, CH⋅⋅⋅π interactions, and hydrophobic effect. Due to the dynamically-rotational propeller chirality of TPE units, 1 with adaptive chirality can further serve as a chiroptical sensor to exhibit opposite Cotton effects with mirror-image CD spectra for the pH-dependent hydrogen-bonded assemblies of d(GpC) including the Watson-Crick G ⋅ C ⋅ G ⋅ C (pH 9.22) and Hoogsteen G ⋅ C+ ⋅ G ⋅ C+ (pH 5.74) quartets through the host-guest chirality transfer in water.

Tetraphenylethene-Based cis/trans Isomers for Targeted Fluorescence Sensing and Biomedical Applications.

Molecular probes which can be modulated, functionalized and used to visualize the processes are highly desirable for understanding and manipulating biological systems. Geometric cis and trans isomers of tetraphenylethene (TPE) emerge as attractive candidates to fulfill these tasks thanks to the unique aggregation-induced emission properties, tailorable structures, and responsiveness to external stimuli. This minireview focuses on cis and trans isomers of TPE derivatives that are functionalized with molecular recognition units for fluorescence detection, bioimaging and cancer therapy. The effects of molecular geometry on fluorescence property, target binding ability and biological activity are summarized. The feasibility to in vitro and in vivo switch molecular configuration and thus bio-activity is discussed. Finally, the future development and challenges are discussed in view of TPE-based stereoisomers for targeted sensing and imaging-guided modulation of biological processes.

One-dimensional coordinated polymers of tetraphenylethene pyridine and copper-iodide for fluorescence detection of nitroaromatic explosives.

The spatial arrangement of molecules plays a crucial role in determining the macroscopic properties of functional materials. Coordinated polymers (CPs) formed by self-assembly of organic isomeric ligands and metals offer unique performance characteristics. In this study, we present the investigation of a one-dimensional CP, named CIT-E, composed of tetraphenylethene pyridine derivative (TPE-2by-2-E) ligands and copper iodide. The resulting CP exhibits a one-dimensional bead chain structure with exceptional thermal and chemical stability. By leveraging the competitive absorption between CIT-E and the explosive analog 2,4-dinitroaniline, we achieve detection of the explosive through changes in the absorption intensity of the excitation light source and subsequent fluorescence response. The CP demonstrates high selectivity and anti-interference ability in detecting 2,4-dinitroaniline in aqueous solution, with a detection linear range of 0.1 to 300 µM and a detection limit of 0.05 µM, surpassing the national third-level emission standard. These findings highlight the potential of CP CIT-E as a promising material for the detection of explosive nitroaromatic compounds.

Tetraphenylethene Derivatives Bearing Alkylammonium Substituents: Synthesis, Chemical Properties, and Application as BSA, Telomere DNA, and Hydroxyl Radical Sensors.

Tetraphenylethene derivatives (TPEs) are used as luminescence probes for the detection of metal ions and biomolecules. These sensors function by monitoring the increase in the photoluminescence (PL) intensity of the TPEs resulting from aggregation-induced emission (AIE) upon interaction with the analytes. The AIE behavior of the sensors was investigated by measuring their PL. In this study, PL, PL lifetime, and confocal laser scanning microscopy measurements were carried out as part of our in-depth investigation of AIE behavior of TPEs for the detection of biomolecules and radical species. We used 1,1,2,2-tetrakis(4-((trimethylammonium)alkoxy)phenyl)tetraphenylethene tetrabromide (TPE-C(m)N+Me3Br-, m = 2, 4, and 6, where m denotes the number of methylene groups in the alkyl chain) and TPE-C(m)N+Me3TCNQ-• (TCNQ-• is the 7,7',8,8'-tetracyanoquinodimethane anion radical) as luminescent probes for the detection of bovine serum albumin (BSA), DNA, and the hydroxyl radical (•OH) generated from Fenton's reagent. The sensing performance of TPE-C(m)N+Me3Br- for BSA and DNA was found to depend on the length of the alkyl chains (m). UV-vis and PL measurements revealed that the responses of TPE-C(m)N+Me3Br- and TPE-C(4)N+TCNQ-• to Fenton's reagent depended on the solvent. The electrochemical properties of the TPE derivatives prepared in this study were additionally investigated via cyclic voltammetry.

Controlling the Fluorescence Performance of AIE Polymers by Controlling the Polymer Microstructure.

Aggregation-induced emission (AIE) polymers with expected emission wavelength/color and fluorescence efficiency are valuable in applications. However, most AIE polymers exhibit irregular emission wavelength/color changes compared to the original AIE monomers. Here, we report the synthesis of AIE polymers with unchanged emission wavelength by ring-opening (co)polymerizations of 4-(triphenylethenyl)phenoxymethyloxirane (TPEO) and other epoxides or phthalic anhydride. The chemical structures/physical properties of all (co)polymers were characterized by NMR, SEC, MALDI-TOF, and DSC. The co-polyether microstructures were revealed by calculating the reactivity ratios and visualized by Monte Carlo simulation. The photoluminescence quantum yields of all the (co)polymers were determined in the solid state. We systematically correlated the fluorescence performance with molecular weights, crystallinity, monomer compositions, glass transition temperatures, side lengths, and flexibility/rigidity.

Tuning Proapoptotic Activity of a Phosphoric-Acid-Tethered Tetraphenylethene by Visible-Light-Triggered Isomerization and Switchable Protein Interactions for Cancer Therapy.

We herein report a phosphoric-acid-substituted tetraphenylethene (T-P) capable of adapting its geometric configuration and biological activity to the microenvironment upon light irradiation for apoptosis modulation. Different from most ultraviolet-responsive isomerization, T-P undergoes cis-trans isomerization under visible light irradiation, which is biocompatible and thus photo-modulation is possible in living biosystems. By using alkaline phosphatase (ALP) and albumin as dual targets, T-P isomers display different protein binding selectivity, cancer-cell internalization efficiency and apoptosis-inducing ability. The proapoptotic activity was found to be kinetically controlled by the enzymatic reaction with ALP and regulated by co-existing albumin. Motivated by these findings, two-way modulation of proapoptotic effect and on-demand boosting anticancer efficacy were realized in vitro and in vivo using light and endogenous proteins as multiple non-invasive switching stimuli.

A Fluorescent Cage for Supramolecular Sensing of 3-Nitrotyrosine in Human Blood Serum.

3-Nitrotyrosine (NT) is generated by the action of peroxynitrite and other reactive nitrogen species (RNS), and as a consequence it is accumulated in inflammation-associated conditions. This is particularly relevant in kidney disease, where NT concentration in blood is considerably high. Therefore, NT is a crucial biomarker of renal damage, although it has been underestimated in clinical diagnosis due to the lack of an appropriate sensing method. Herein we report the first fluorescent supramolecular sensor for such a relevant compound: Fluorescence by rotational restriction of tetraphenylethenes (TPE) in a covalent cage is selectively quenched in human blood serum by 3-nitrotyrosine (NT) that binds to the cage with high affinity, allowing a limit of detection within the reported physiological concentrations of NT in chronic kidney disease.

Anti-cancer adjuvant drug screening via epithelial-mesenchymal transition-related aptamer probe.

Epithelial-mesenchymal transition (EMT) is implicated in the pathological processes of cancer metastasis and drug resistance. Anti-cancer drugs may also potentially lead to EMT, resulting in their reduced therapeutic effect. Therefore, the combination of these anti-cancer drugs with anti-EMT agents has been promoted in clinic. Screening anti-EMT drugs and evaluation of EMT process are highly dependent on EMT biomarkers on cell membrane. At present, the detection of EMT biomarker is mainly by Western blot method, which is time-consuming and complicated. In this work, for effectively screening anti-EMT drugs by evaluation of the EMT process, a type of aptamer probe based on aggregation-induced emission (AIE) was designed. The aptamer SYL3C was employed to target the EMT biomarker EpCAM on cell membrane. Two fluorophores, FAM and tetraphenylethene (TPE, an AIE dye), were modified at the two ends of SYL3C, respectively. This aptamer probe (TPE-SYL3C-FAM) can monitor the EpCAM expression, which can be recovered by anti-EMT drugs. By observation of the change in TPE emission intensity, the anti-EMT effect of drugs can be evaluated. The FAM emission was used as internal reference to reduce environmental interferences. This probe can be potentially used to screen anti-EMT agents as anti-cancer adjuvant drugs with high throughput.

Adaptive Chirality of an Achiral Cucurbit[8]uril-Based Supramolecular Organic Framework for Chirality Induction in Water.

Chiral framework materials have been developed for many applications including chiral recognition, chiral separation, asymmetric catalysis, and chiroptical materials. Herein, we report that an achiral cucurbit[8]uril-based supramolecular organic framework (SOF-1) with the dynamic rotational conformation of tetraphenylethene units can exhibit adaptive chirality to produce M-SOF-1 or P-SOF-1 with mirror-image circular dichroism (CD) with gabs ≈±10-4 and circularly polarized luminescence (CPL) with glum ≈±10-4 induced by L-/D-phenylalanine in water, respectively. The chirality induction in CD (gabs ≈-10-4 ) and CPL (glum ≈-10-4 ) of P-SOF-1 from achiral SOF-1 can be presented by using a small amount of adenosine-5'-triphosphate disodium (ATP) or adenosine-5'-diphosphate disodium (ADP) (only 0.4 equiv) in water. Furthermore, the adaptive chirality of SOF-1 can be used to determine dipeptide sequences (e.g., Phe-Ala and Ala-Phe) and distinguish polypeptides/proteins (e.g., somatostatin and human insulin) with characteristic CD spectra. Therefore, achiral SOF-1 as an ideal chiroptical platform with adaptive chirality may be applied to determine the enantiopurity of amino acids (e.g., L-/D-phenylalanine), develop aqueous CPL materials, and distinguish biological chiral macromolecules (e.g., peptides/proteins) via chirality induction in water.

Microlasers from AIE-Active BODIPY Derivative.

Organic microlasers have attracted much attention due to their unique features such as high mechanical flexibility, facile doping of gain materials, high optical quality, simplicity and low-cost fabrication. However, organic gain materials usually suffer from aggregation-caused quenching (ACQ), preventing further advances of organic microlasers. Here, a new type of microlaser from aggregation-induced emission (AIE) material is successfully demonstrated. By introducing a typical noncrystalline AIE material, a high quality microlaser is obtained via a surface tension-induced self-assembly approach. Distinct from conventional organic microlasers, the organic luminescent material used here is initially nonluminescent but can shine after aggregation under optical pumping. Further investigations demonstrate that AIE-based microlasers exhibit advantages to enable much higher doping concentrations, which provides an alternative way to improved lasing performance including dramatically reduced threshold and favorable lasing stability. It is believed that these results could provide a promising way to extend the content of microlasers and open a new avenue to enable applications ranging from chemical sensing to biology.

Detection of DNA methyltransferase activity using template-free DNA polymerization amplification based on aggregation-induced emission.

A sensitive and selective fluorescence assay for DNA methyltransferase (MTase) activity detection was designed based on aggregation-induced emission (AIE) and target initiated template-free DNA polymerization. Quaternized tetraphenylethene salt was synthesized as the AIE probe, which binds to single-stranded DNA by electrostatic interaction. A hairpin probe was designed with a specific sequence for DNA MTase. In the presence of DNA MTase, the methylation reaction initiated DNA polymerization with terminal deoxynucleotidyl transferase (TdT), which activated the fluorescence intensity through AIE. The designed DNA sensor displayed a linear response to concentrations of DNA adenine methyltransferase (Dam) MTase from 0.5 U·mL-1 to 100 U mL-1, with a limit of detection of 0.16 U mL-1. The assay was also effective for detection of DNA MTase activity in human serum and for showing the inhibitory effect of 5-fluorouracil on Dam MTase.

Spatiotemporal Dynamics of Aggregation-Induced Emission Enhancement Controlled by Optical Manipulation.

We present spatiotemporal control of aggregation-induced emission enhancement (AIEE) of a protonated tetraphenylethene derivative by optical manipulation. A single submicrometer-sized aggregate is initially confined by laser irradiation when its fluorescence is hardly detectable. The continuous irradiation of the formed aggregate leads to sudden and rapid growth, resulting in bright yellow fluorescence emission. The fluorescence intensity at the peak wavelength of 540 nm is tremendously enhanced with growth, meaning that AIEE is activated by optical manipulation. Amazingly, the switching on/off of the activation of AIEE is arbitrarily controlled by alternating the laser power. This result means that optical manipulation increases the local concentration, which overcomes the electrostatic repulsion between the protonated molecules, namely, optical manipulation changes the aggregate structure. The dynamics and mechanism in AIEE controlled by optical manipulation will be discussed from the viewpoint of molecular conformation and association depending on the laser power.

Self-Assembly and Fluorescence of Tetracationic Liquid Crystalline Tetraphenylethene.

A series of tetraguanidinium tetraphenylethene (TPE) arylsulfonates with different chain lengths was prepared via ionic self-assembly of tetraguanidinium TPE chloride and the respective methyl arylsulfonates. Liquid crystalline properties were studied by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. Tetraguanidinium TPE arylsulfonates with chain lengths of C8 -C12 displayed hexagonal columnar mesophases over a broad temperature range, while derivatives with longer chains showed oblique columnar phases. In solution all compounds displayed aggregation-induced emission behaviour. Temperature-dependent luminescence spectra of the bulk phase of the tetraguanidinium TPE arylsulfonate with C14 side chains revealed a strong luminescence both in the solid state and the oblique columnar mesophase. The emission behaviour was rationalized by a unique combination of restriction of intramolecular rotation of the TPE core, Coulomb interaction between the guanidinium cations and π-π interactions of the anionic arylsulfonate moieties.

Spectroscopic and Theoretical Characterization of Through-Space Conjugation of Foldamers with a Tetraphenylethene Hinge.

Through-space conjugation is an important noncovalent interaction in artificial materials and biomacromolecules. Establishing relationships between geometry and property is of high significance to provide deeper insights into this phenomenon. In this work, we have focused on the through-space conjugation in a new class of foldamers with a folded tetraphenylethene core. We have studied its impact on the photophysical properties through experimental measurements and theoretical calculations. It is found that the through-space conjugation makes significant contributions to the short-wavelength absorption in these foldamers. Moreover, these foldamers exhibit aggregation-enhanced emission (AEE) and apparent blue shifts in their emission spectra on going from solution to aggregates. The structural changes are smaller in the aggregated state than those in the isolated state during the excited-state relaxation process, which results in lower re-organization energies. This accounts for the blueshifted and enhanced emissions in the aggregates.

A Novel Water-Soluble Fluorescence Probe with Wash-Free Cellular Imaging Capacity Based on AIE Characteristics.

A potential real-time imaging water-soluble fluorescent polymer (P3) is facilely prepared via one-pot method. For P3, tetraphenylethene unit serves as the fluorescent unit, poly(acryloyl ethylene diamine) (a kind of polyelectrolyte) with specific degree of polymerization acts as water-soluble part. 1 H-NMR, gel permeation chromatography (GPC), UV-vis spectroscopy, photoluminescence (PL), and confocal laser scanning microscopy are undertaken to characterize the structure and property of P3. The results of wash-free cellular imaging show that the signal-to-noise ratio is high as the concentration of P3 is 50 µg mL-1 . In addition, the pH-responsive and Cd2+ -responsive are also investigated in this paper. The results coming from pH-responsive show that P3 solution displays significant fluorescence under near neutral. And the result from the cellular imaging shows that intracellular fluorescence intensity enhances with the augment of concentration of Cd2+ , which reveals that P3 can give a hint to resolve the dilemma of traditional fluorescent dyes used as living cellular fluorescent probe.

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.

Polysiloxane-Modified Tetraphenylethene: Synthesis, AIE Properties, and Sensor for Detecting Explosives.

Polysiloxane-modified tetraphenylethene (PTPESi) is successfully synthesized by attaching tetraphenylethene (TPE) units onto methylvinyldiethoxylsiloxane and subsequent polycondensation. Introducing polysiloxane into TPE has minimal effect on the photophysical properties and aggregation-induced emission behavior of TPE. The highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) energy levels of PTPESi are located mainly on the tetraphenylethene moieties. The fluorescence intensity and the half width of the emission peak of PTPESi before and after annealing at 120 °C for 12 h are nearly the same, indicating high thermal stability and morphological stability. In addition, use of PTPESi film as a sensor toward the vapor-phase detection of explosives is also studied and it displays quite high fluorescence quenching efficiency and good reversibility.

Tetraphenylethene Derivatives with Different Numbers of Positively Charged Side Arms have Different Multimeric G-Quadruplex Recognition Specificity.

Some G-rich sequences in the human genome have the potential to fold into a multimeric G-quadruplex (G4) structure and the formation of telomeric multimeric G4 has been demonstrated. Searching for highly specific multimeric G4 ligands is important for structure probing and for study of the function of G-rich gene sequences, as well as for the design of novel anticancer drugs. We found different numbers of positively charged side-arm substituents confer tetraphenylethene (TPE) derivatives with different multimeric G4 recognition specificity. 1,2-Bis{4-[(trimethylammonium)butoxy]phenyl}-1,2-tetraphenylethene dibromide (DATPE), which contains two side arms and gives a fluorescence response to only multimeric G4, has a low level of cytotoxicity and little or no effect on multimeric G4 conformation or stability. These features make DATPE a promising fluorescent probe for detection of multimeric G4 specifically in biological samples or in vivo. 1,1,2,2-Tetrakis{4-[(trimethylammonium)butoxy]phenyl}tetraphenylethene tetrabromide (QATPE), which contains four side arms, has a lower level of specificity for multimeric G4 recognition compared to DATPE but its binding affinity to multimeric G4 is higher compared to other structural DNAs. Its high multimeric G4-binding affinity, excellent multimeric G4-stabilizing ability, and the promotion of parallel G4 formation make QATPE a good candidate for novel anticancer drugs targeting multimeric G4 specifically, especially telomeric multimeric G4. This work provides information that might aid the design of specific multimeric G4 probes and the development of novel anticancer drugs.

Restriction of intramolecular motions: the general mechanism behind aggregation-induced emission.

Aggregation-induced emission (AIE) has been harnessed in many systems through the principle of restriction of intramolecular rotations (RIR) based on mechanistic understanding from archetypal AIE molecules such as tetraphenylethene (TPE). However, as the family of AIE-active molecules grows, the RIR model cannot fully explain some AIE phenomena. Here, we report a broadening of the AIE mechanism through analysis of 10,10',11,11'-tetrahydro-5,5'-bidibenzo[a,d][7]annulenylidene (THBDBA), and 5,5'-bidibenzo[a,d][7]annulenylidene (BDBA). Analyses of the computational QM/MM model reveal that the novel mechanism behind the AIE of THBDBA and BDBA is the restriction of intramolecular vibration (RIV). A more generalized mechanistic understanding of AIE results by combining RIR and RIV into the principle of restriction of intramolecular motions (RIM).