Tetraphenylethene Derivatives Research Articles

Polymorphous meso-Dicyanovinyl-Substituted Tetraphenylethylene Derivative Showing Distinguishing Two-Color Emission and Ultrahigh-Contrast Mechano-Responsive Luminescence Behavior

Polymorphous <i>meso</i>-Dicyanovinyl-Substituted Tetraphenylethylene Derivative Showing Distinguishing Two-Color Emission and Ultrahigh-Contrast Mechano-Responsive Luminescence Behavior

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.

Dual-emitting cellulose nanocrystal hybrid materials with circularly polarized luminescence for anti-counterfeiting labels

Cellulose nanocrystal (CNC) hybrid materials with numerous optical states have great potential as anti-counterfeiting labels and information encryption materials. However, it is challenging to construct multicolor emitting materials with tunable behaviors, which can dramatically enhance anti-counterfeiting abilities. Here, free-standing composite films with vivid multi-structural colors and dual-emitting fluorescence are successfully fabricated through a host-guest coassembly strategy. The lanthanide complex and an aggregation-induced emission molecule (tetraphenylethylene derivative, TPEC) are selected as luminescent guests, which are integrated into the chiral nematic structure of CNCs. The obtained photonic films display broadband reflection across the visible spectrum, which may be attributed to the chiral nematic domains with variations in the helical pitches and helical axis orientations. Under 254 nm excitation, the film exhibits bright red emission, while blue–green emission switching occurs under 365 nm excitation. The broad reflection band of the film covers both the green and red fluorescent emission centers, and right circularly polarized luminescence emission with different dissymmetry factors is produced due to the selective reflection of the left chiral nematic structure. A large glum value up to −0.21 at 600 nm was realized. Additionally, CNC-based materials with tailored shapes are further used in anti-counterfeit tags and decorative applications.

Chiral Supramolecular Multiblock Copolymerization Accompanying Chirality Transfer in Heterostructures via Living Chain Growth

AbstractWe report the unique synthesis of chiral supramolecular tri‐ and penta‐BCPs with controllable chirality using kinetically adjusted seeded supramolecular copolymerization in THF and DMSO (99 : 1, v/v). Tetraphenylethylene (d‐ and l‐TPE) derivatives bearing d‐ and l‐alanine side chains formed thermodynamically favored chiral products via a kinetically trapped in monomeric state with a long lag phase. In contrast, achiral TPE‐G containing glycine moieties did not form a supramolecular polymer owing to the energy barrier in its kinetically trapped state. We show that the copolymerization of the metastable states of TPE‐G not only enables the generation of supramolecular BCPs by the seeded living growth method, but also transfers chirality at the seed ends. This research demonstrates the generation of chiral supramolecular tri‐ and penta‐BCPs with B‐A‐B, A‐B‐A‐B‐A, and C‐B‐A‐B‐C block patterns accompanying chirality transfer via seeded living polymerization.

Chiral Supramolecular Multiblock Copolymerization Accompanying Chirality Transfer in Heterostructures via Living Chain Growth.

We report the unique synthesis of chiral supramolecular tri- and penta-BCPs with controllable chirality using kinetically adjusted seeded supramolecular copolymerization in THF and DMSO (99 : 1, v/v). Tetraphenylethylene (d- and l-TPE) derivatives bearing d- and l-alanine side chains formed thermodynamically favored chiral products via a kinetically trapped in monomeric state with a long lag phase. In contrast, achiral TPE-G containing glycine moieties did not form a supramolecular polymer owing to the energy barrier in its kinetically trapped state. We show that the copolymerization of the metastable states of TPE-G not only enables the generation of supramolecular BCPs by the seeded living growth method, but also transfers chirality at the seed ends. This research demonstrates the generation of chiral supramolecular tri- and penta-BCPs with B-A-B, A-B-A-B-A, and C-B-A-B-C block patterns accompanying chirality transfer via seeded living polymerization.

Aggregation-Induced Emission Luminogen-Encapsulated Fluorescent Hydrogels Enable Rapid and Sensitive Quantitative Detection of Mercury Ions.

Hg2+ contamination in sewage can accumulate in the human body through the food chains and cause health problems. Herein, a novel aggregation-induced emission luminogen (AIEgen)-encapsulated hydrogel probe for ultrasensitive detection of Hg2+ was developed by integrating hydrophobic AIEgens into hydrophilic hydrogels. The working mechanism of the multi-fluorophore AIEgens (TPE-RB) is based on the dark through-bond energy transfer strategy, by which the energy of the dark tetraphenylethene (TPE) derivative is completely transferred to the rhodamine-B derivative (RB), thus resulting in intense photoluminescent intensity. The spatial networks of the supporting hydrogels further provide fixing sites for the hydrophobic AIEgens to enlarge accessible reaction surface for hydrosoluble Hg2+, as well create a confined reaction space to facilitate the interaction between the AIEgens and the Hg2+. In addition, the abundant hydrogen bonds of hydrogels further promote the Hg2+ adsorption, which significantly improves the sensitivity. The integrated TPE-RB-encapsulated hydrogels (TR hydrogels) present excellent specificity, accuracy and precision in Hg2+ detection in real-world water samples, with a 4-fold higher sensitivity compared to that of pure AIEgen probes. The as-developed TR hydrogel-based chemosensor holds promising potential as a robust, fast and effective bifunctional platform for the sensitive detection of Hg2+.

Tetraphenylethene-based macrocycles: Visualized monitoring the hydrolysis of silicon-oxygen bond and their tunable luminescent properties

The preparation of silicone material is generally carried out by hydrolytic condensation, and various methods have been tried so far to study the kinetics of silicon-oxygen bond hydrolysis. However, the process and kinetics of silicon-oxygen bond hydrolysis cannot be efficiently monitored in real-time due to the limitations of traditional testing methods. In the present study, we have successfully designed and synthesized a series of circular tetraphenylethylene (TPE) derivatives connected with different lengths of the siloxanes chain. As the chain length gets longer, the restriction on phenyl rotation in TPE derivatives becomes weaker, which induced fluorescence quenching gradually at the molecular level. Hence, it provides the most direct and convincing evidence for the effect of chain lengths in the popular restricted intramolecular rotation (RIR) mechanism with aggregation-induced emission (AIE) phenomenon. The strong fluorescent molecule was used to monitor the kinetics of silicon-oxygen bond hydrolysis in real-time successfully by the AIE method with the RIR mechanism. The high sensitivity and efficiency of fluorescence provide an unparalleled “visualization” window for real-time monitoring of the kinetic control of Si-O bond hydrolysis. Furthermore, the half-life and reaction kinetic data of Si-O bond-breaking reaction by different pH are obtained to provide a reference for scientists and engineers not only in fundamental research but also in industrial production. Finally, the aggregation-induced color-tunable emission was obtained with the different aggregation forms of molecules, exhibiting a promising potential for intelligent luminescent materials.

Emission‐Tunable Nanofluorophores through Self‐assembly of Amphiphilic Block Copolymers: toward Application in Cell Imaging

Comprehensive SummaryNanofluorophores based on aggregation‐induced emission (AIE) dyes have recently received considerable attention because of their unique optical properties and biocompatibility. In this work, we report an emission‐tunable nanofluorophore constructed by the self‐assembly of an amphiphilic block copolymer (denoted by PTN). The diblock copolymer was synthesized by RAFT polymerization. A polyethylene glycol‐based trithiocarbonate was employed as the macromolecular chain transfer agent, and a near‐infrared emitting tetraphenylethylene derivative with a vinyl terminal group was designed as the monomer. The block copolymers self‐assembled in an aqueous solution to form nanospheres, which showed near‐infrared emission at approximately 720 nm with a significant Stokes shift of approximately 260 nm. Furthermore, nanofluorophores have excellent biocompatibility, photostability, and pH‐independent emission‐tunable properties, and were successfully applied to label HeLa cells for fluorescence imaging.

Facile Hydrogels of AIEgens Applied as Reusable Sensors for In Situ and Early Warning of Metallic Corrosion

Early detection of metallic corrosion is one considerable method to reduce imperceptible disasters nowadays. Fluorescent coatings with high sensitivity and long lifetimes for use in the early detection of metallic corrosion are in high demand, but they are presently difficult to prepare. Inspired by the chameleon's skin, which is capable of switching its color in different atmospheres sensitively and reversibly, we proposed herein a facile and universal all-in-one strategy of combining the fluorescent sensitivity and dynamic hydrogen bonds in a hydrogel to develop a reusable corrosion detection tape to cover metal surfaces. The fluorescent hydrogel tape was constructed using free radical copolymerization of monomers [hydroxyethyl methylacrylate (HEMA) and tetraphenylethene derivatives (TPEPy)]. Due to the aggregation-induced emission (AIE) behavior of TPEPy, the poly(HEMA-co-TPEPy) hydrogel is capable of monitoring the traces of corrosion via the release of ferric ions with a concentration as low as 10-5 M. Moreover, due to the dynamic hydrogen bonds of hydroxyethyl groups in hydrogel networks, the fluorescent hydrogel tape exhibited good adhesion and well reusability for over 10 applications to effectively warn against early corrosion of stainless steel. This non-destructive and reversible method of early corrosion detection can provide valuable signals when maintenance is needed before the metal suffers serious damage.

Different Stepwise Growth Mechanism of AIE-Active Tetraphenylethylene-Functionalized Metal-Organic Frameworks on Au(111) and Cu(111) Surfaces.

Fabricating tetraphenylethylene (TPE)-functionalized metal-organic frameworks (MOFs) with aggregation- induced emission on surfaces and understanding the growth mechanism have not yet been pursued. Herein, MOFs constructed via the Ullmann-type reaction of a C2-symmetry TPE derivative (p-BrTBE) on Au(111) and Cu(111) surfaces were thoroughly investigated using scanning tunneling microscopy. On a Au(111) surface, p-BrTBE molecules formed the self-assembled pattern at 298 K. Stepwise annealing led to a progressive evolution process, in which the stepwise debromination reaction led to organometallic intermediates, and surface-stabilized radicals and metal-organic networks were formed. By contrast, the relatively ordered MOFs were obtained by replacing the underlying substrate with the more catalytically active Cu(111) at 298 K. Density functional theory calculations demonstrated that the formation of different networks on Au(111) and Cu(111) was determined by the different conformations of the TBE unit on the different substrates due to the different adsorption energy.

Construction of aggregation-induced emission monolayer at the air/water interface

Construction of aggregation-induced emission monolayer at the air/water interface Kohei Iritani, Department of Applied Chemistry, School of Engineering, Tokyo University of Technology. Organic fluorescent materials using a molecule with aggregation-induced emission (AIE) effect have intense interest due to their potential utilities such as flexible display devices and photovoltaics. For the applications to two-dimensional devices, we purposed the construction of a monolayer formed by a tetraphenylethylene (TPE) derivative as an AIE molecule at the air/water interface. To this end, we synthesized amphiphilic TPE derivatives. We found that the TPE derivative formed a thin film with blue- green emission on the water surface. Moreover, from AFM observations, we confirmed that the transferred film had monolayer thickness.

Fluorescence Turn-on of Tetraphenylethylene Derivative by Transfer from Cyclodextrin to Liposomes, HeLa Cells, and E. coli.

Herein, trimethyl-β-cyclodextrin (TMe-β-CDx) and γ-cyclodextrin (γ-CDx) could dissolve a tetraphenylethylene derivative (TPE-OH4 ) in water through high-speed vibration milling. The fluorescence intensity of the TMe-β-CDx-TPE-OH4 complex was much higher than that of the γ-CDx-TPE-OH4 complex, as the rotation of the central C=C double bond of TPE-OH4 after photoactivation was inhibited in a smaller TMe-β-CDx cavity in comparison with the γ-CDx cavity. In contrast, the fluorescence intensity of the γ-CDx-TPE-OH4 complex was very weak; nevertheless, it increased after the addition of liposomes due to the transfer of TPE-OH4 from the γ-CDx cavity to the lipid membrane as a "turn-on" phenomenon. Furthermore, to apply temperature sensor, it was demonstrated that the fluorescence intensity in the liposomes depended on the phase-transition temperature. By using the fluorescence turn-on phenomenon, TPE-OH4 could detect the presence of HeLa cells and E. coli by fluorescence.

Deciphering the ultrafast dynamics of a new tetraphenylethylene derivative in solutions: charge separation, phenyl ring rotation and CC bond twisting.

Tetraphenylethylene (TPE) derivatives are one of the fundamental units for developing aggregation induced emission (AIE) scaffolds. However, the underlying mechanisms implicated in the relaxation of the excited TPE remain a topic of ongoing discussion, while the effect of bulky substituents on its photobehaviour is still under scrutiny. Here, we report a detailed study of the photophysical properties of a new symmetrical and bulky TPE derivative with terphenyl groups (TTECOOBu) in solvents of different polarities and viscosities. Using femto- to nanosecond (fs-ns) time-resolved absorption and emission techniques, we elucidated the role of the phenyl group rotations and core ethylene bond twisting in its behaviour. We demonstrate that TTECOOBu in DCM solutions undergoes a 600 fs charge separation along the ethylene bond leading to a resonance structure with a lifetime of ∼1 ns. The latter relaxes via two consecutive events: a twisting of the ethylene bond (∼ 9 ps) and a rotation of the phenyl rings (∼ 30 ps) leading to conformationally-relaxed species with a largely Stokes-shifted emission (∼ 12 500 cm-1). The formation of the red-emitting species clearly depends on the solvent viscosity and rigidity of the medium. Contrary to the photobehavior in the highly viscous triacetin or rigid polymer matrix of PMMA, a reversible mechanism was observed in DCM and DMF solutions. These results provide new findings on the ultrafast mechanisms of excited TPE derivatives and should help in the development of new molecular rotors with interesting AIE properties for photonic applications.

Photocyclization reaction and related photodynamics in the photoproducts of a tetraphenylethylene derivative with bulky substituents: unexpected solvent viscosity effect.

Tetraphenylethylene (TPE) derivatives are ones of the most versatile building blocks showing aggregation-induced emission (AIE). However, their applications are limited by the photophysical and photochemical processes that occur in their excited state. Herein, we report a detailed study of the photochemical behaviour of a new TPE derivative with bulky terphenyl groups (TTECOOBu) in solvents of different viscosities and in a PMMA film. UV light irradiation shows an efficient photocyclization reaction, which produces a 9,10-diphenylphenanthrene (DPP) derivative photoproduct. The emission spectra of the irradiated samples show intermediate (∼420 nm) and final (∼380 nm) species. The photocyclization events are more efficient in environments of higher viscosities or rigidity. We show that in a photoirradiated PMMA film containing TTECOOBu, it is possible to etch a message for more than 1 year. The kinetics is dictated by the motions of the phenyl rings and is faster when their motions are precluded or inhibited. We also elucidated the femto- to millisecond photodynamics of the intermediate and final photoproducts and provide a full picture of their relaxation, with the latter in ∼1 ns at S1 and ∼1 μs at T1. We also demonstrate that the kinetics of the bulky TTECOOBu is much slower than that of the TPE core. Our results also show that both photoevents are not reversible contrary to the case of TPE kinetics. We believe that these results will shed more light on the photochemical behaviour of TPE derivatives and should help in the development of novel TPE-based materials with improved photostability and photo-properties.

Regulating the luminescence of tetraphenylethene (TPE)-based lanthanide nanoparticles in the presence of organic amines/acids

Single ligand (TPE derivatives) and dual ligand (TPE derivatives and ABM)-modified EuVO4 nanoparticles show distinct luminescent responses to aniline and citric acid, respectively.

Self-assembled super-small AIEgen nanoprobe for highly sensitive and selective detection of protamine and trypsin.

Amphiphilic aggregation-induced emission (AIE) molecules show superior potential for fabricating novel ultrasmall nanoprobes. Here, an anionic dipyridyl tetraphenylethene (TPE) derivative is rationally designed and a super-small self-assembled AIEgen nanoprobe (TPE-2Py-SO3NaNPs, ca. 2.48 nm) is thus conveniently constructed for the supersensitive detection of protamine and trypsin. In HEPES/DMSO solution (8 : 2, v/v, pH = 7.4), negatively charged TPE-2Py-SO3NaNPs exhibited an AIE effect in the presence of positively charged protamine, presenting a fluorescence enhancement at 498 nm together with a large Stokes shift of 150 nm and a low detection limit of 8.0 ng mL-1. In addition, the in situ formed TPE-2Py-SO3Na/protamine nanocomposite can be dissociated by trypsin due to the highly selective degradation of protamine via enzymatic hydrolysis, achieving a detection limit for trypsin as low as 5.0 ng mL-1.

An AIE active fluorescence sensor for measuring Fe3+ in aqueous media and an iron deficiency anemia drug.

In this study, a new tetraphenylethene derivative bearing triazole and pyridine moieties (TPE-TAP) was synthesized using click chemistry. The fluorescence sensing properties of TPE-TAP were investigated in almost 100% aqueous media. For this purpose, first of all, structural characterization of the newly synthesized compound TPE-TAP was performed by NMR and HRMS analyses. Then, the optical behavior of TPE-TAP was investigated in different ratios of a THF-water mixture (0-98%). The obtained results showed that the best fluorescence for TPE-TAP was observed in the presence of 98% water in the medium. Then, the ion selectivity of TPE-TAP was determined using 19 different cations in the THF-water medium (2 : 98 v/v%). It was observed that among the cations studied, only Fe3+ quenched the fluorescence of TPE-TAP. The detection limit and binding constant values of TPE-TAP for Fe3+ were calculated as 1.3 μM and 26.65 M-2, respectively, from the graph results of the decrease in the fluorescence intensity of TPE-TAP in the presence of Fe3+ at different concentrations. In addition, the study investigating the selectivity of TPE-TAP in the presence of 18 cations other than Fe3+ showed that none of the studied cations interfered with Fe3+. Practical application of TPE-TAP was also carried out using a commercial iron drug. All results showed that TPE-TAP is a fluorometric sensor highly selective, sensitive, and suitable for practical application for Fe3+ ions in aqueous medium.

Molecular engineering to enhance the reactive oxygen species generation of AIEgens and exploration of their versatile applications.

Fluorescent dyes with aggregation-induced emission (AIE) characteristics have shown potential applications in the fields of biological imaging, photodynamic therapy and photothermal therapy, in which photosensitizers (PSs) play a crucial role. However, how to design high-quality PSs with high reactive oxygen species (ROS) generation efficiency remains unclear. In this contribution, an effective molecular design strategy to improve the ROS generation efficiency of AIE PSs was proposed. A series of tetraphenylethylene derivatives containing the pyridine ring or pyridinium with different substituents were designed and synthesized. All the molecules were weakly emissive when molecularly dissolved in solution but displayed intense emission upon aggregation, demonstrating a phenomenon of AIE characteristic. Pyridinium molecules could be used as visualization agents to specifically stain the mitochondria in living cells, while most of the molecules failed to generate ROS upon white light irradiation. In contrast, TPE-Pys-BP containing benzophenone produced ˙OH and 1O2 efficiently in the presence of light due to its large spin-orbit coupling constant to promote efficient intersystem crossing. Such a property allowed TPE-Pys-BP to serve as a PS to kill cancer cells using photodynamic therapy. TPE-Pys-BP also exhibited mechanochromic luminescence (ML), and its emission could be reversibly switched between two distinct colors through repeated grinding and fuming processes. A security paper was fabricated using the ML properties of TPE-Pys-BP.

Multifunctional Fluorescent Materials with Reversible Mechanochromism and Distinct Photochromism

AbstractIt is extremely significant and desirable to integrate the fascinating mechanochromism and photochromism in one simple molecule. Herein, two intriguing cyanostilbene‐containing triphenylamine (TPA)/tetraphenylethylene (TPE) derivatives (Z‐TPA‐MB and Z‐TPE‐MB) are elaborately designed, which not only display excellent aggregation‐induced emission (AIE) properties with high solid‐state fluorescence quantum yields (60.9% and 63.8%) but also exhibit reversible and high contrast mechanochromism and distinct photochromism. The powders of Z‐TPA‐MB and Z‐TPE‐MB both exhibit large red‐shift under mechanical stimulation based on the highly twisted conformation and the resulting loose packing mode, accompanied by significant changes in apparent and fluorescent colors. Meanwhile, their solid‐state fluorescence can be reversibly switched between crystalline and amorphous structures through alternating grinding and solvent fuming, exhibiting good fatigue resistance. In addition, the molecules also exhibit distinct dual‐mode photochromic behaviors owing to the presence of cyanostilbene moieties: under 420/365 nm light irradiation, the fluorescence of which decreases in solution owing to the photo‐isomerization, while decreases and blue‐shifts in the aggregated state owing to the photodimerization reactions. The reversible, tractable, and high‐contrast mechanochromism and distinct photochromism of the cyanostilbene‐containing molecules endow them with excellent application prospects in the field of rewritable papers and photo‐patterning.

9,9-Bis[4-(N-aryl)phenyl]methylidene-xanthylidene Derivatives Displaying Mechano-, Crystallo-, and Thermochromism.

Tetraphenylethylene (TPE) derivatives bearing a xanthene moiety are of interest because they have novel optical properties. 9,9-Bis[4-(N,N-diphenylamino)phenyl] and 9,9-bis[4-(9-carbazolyl)-phenyl]methylidene-xanthylidenes 3 and 4 were synthesized using Suzuki-Miyaura coupling of 9,9-dibromomethylidene-xanthylidene with the corresponding boronic acids. Diphenylamino derivative 3 exhibits mechanochromism and mechanofluorochromism (MC and MFC) reflected in absorption and fluorescence color changes. In contrast, carbazolyl derivative 4 displays thermo- and crystallo-chromism in addition to MC and MFC in the solid state. Powder X-ray diffraction and single crystal X-ray crystallographic analysis reveal that the solid state photophysical properties of these substances are governed by conformational changes rather by the creation of planar π-conjugation extended geometries.