Manipulation of the aggregation and deaggregation of tetraphenylethylene and silole fluorophores by amphiphiles: emission modulation and sensing applications

The preparation of hexaphenylsilole-based conjugated microporous polymer for fluorescence sensing o-nitrophenol

A first hexaphenylsilole-based conjugated microporous polymer, termed THPS, was prepared by a Friedel-Crafts arylation reaction of 1,1,2,3,4,5-hexabenylthirole with 2,4,6-trichloro-1,3,5-triazine catalyzed by anhydrous aluminium trichloride (AlCl3) in 1,2-dichloroethane. Its Brunauer-Emmett-Teller and Langmuir surface area reached up to 1579 and 2081 m2 g-1, and total pore volume and micropore pore volume were severally 0.8325 and 0.7322 cm3 g-1. THPS could fluorescence-sense o-nitrophenol with high sensitivity and selectivity. Its fluorescence quenching constant (KSV) and limits of detection (LODs) were severally 8.32 × 103 L mol-1 and 3.61 × 10-10 mol L-1. The fluorescence quenching of THPS by o-nitrophenol was originated from the combined action of both photo-induced electron transfer mechanism and resonance energy transfer mechanism.

Polyanionic Cyclodextrin-Induced Supramolecular Assembly of a Cationic Tetraphenylethylene Derivative with Aggregation-Induced Emission

The combination of supramolecular chemistry and aggregation-induced emission-based luminogens (AIEgens) has recently attracted tremendous attention because of its ability to offer large emission enhancement even in substantially dilute solutions. In this work, a new aggregation-induced emission (AIE)-based supramolecular assembly has been reported, which consists of a polyanionic cyclodextrin derivative and a tetracationic tetraphenylethylene (TPE) derivative. Ionic cyclodextrins have attracted significant attention in host-guest supramolecular chemistry and pharmaceutical industry. However, ionic derivatives of β-cyclodextrins have not been explored to establish noncovalent interactions-based aggregation assembly of the most popular class of AIEgens, i.e., tetraphenylethylene derivatives. The current report demonstrates AIE of a tetracationic methyl pyridinium derivative of tetraphenylethylene (TPy-TPE) induced by a polyanionic sulfated β-cyclodextrin (S-βCD). The AIE-based supramolecular assembly has been thoroughly investigated using steady-state fluorescence, ground-state absorbance, and time-resolved fluorescence measurements. Further, the response of the supramolecular assembly towards external stimuli, such as, ionic strength, pH, and temperature, has been investigated. In addition, the complexation behavior of the TPE derivative has also been compared with the native neutral β-cyclodextrin derivative, which delineates the important role of the negatively charged portal of S-βCD in inducing aggregation of the TPy-TPE. The stoichiometry of the complex has been found to be 3:1 for TPy-TPE:S-βCD, using Job's plot analysis. Finally, to get insights into the underlying interactions between the supramolecular assembly components, molecular docking calculations have been performed.

AIE materials for cancer cell detection, bioimaging and theranostics

AIE materials exhibit weakly emissive or non-emissive properties in dilute solutions while emit powerful fluorescence in the aggregated/solid state. Recently, AIE based materials have gained immense attention due to their multifunctional role in cancer cell detection, bioimaging and cancer theranostics. In this present book chapter, we will highlight recent advancements of AIE materials for different cancer theranostics applications.

Synthesis and Tetraphenylethylene-Based Aggregation-Induced Emission Probe for Rapid Detection of Nitroaromatic Compounds in Aqueous Media

Tetraphenylethylene (TPE) can be used to construct fluorescent probes with typical aggregation-induced emission (AIE) behavior for next-generation sensing applications. McMurry coupling and Suzuki cross coupling strategies provided the desired sensor thiophene-substituted tetraphenylethylene (THTPE). The synthesized TPE analogues were characterized by NMR spectroscopy and mass spectrometry. Maximum AIE of THTPE was observed in 90% water (H2O/THF) content due to extensive formation of aggregates. The AIE properties of THTPE have been utilized for facile detection of nitroaromatic compounds (NACs) (1.0 nM) through a fluorescence quenching mechanism. A paper strip adsorbed with the AIE-based THTPE fluorophore is developed for rapid and convenient detection of NAC-based analytes. Further, interaction of THTPE with analytes is also studied via Gaussian software at the DFT/B3LYP/6-31G(d) level of theory. Interaction energy, frontier molecular orbitals (FMOs), and non-covalent interaction (NCI) analyses are studied by using the same method. Computational results revealed that nitrobenzene (NB) has the strongest interaction while 1,3-dinitrobenzene (DNB) exhibits the least interaction with the sensor molecule. These computational results clearly demonstrate good agreement with experimental data.

Non-toxic near-infrared light-emitting diodes

Harnessing cost-efficient printable semiconductor materials as near-infrared (NIR) emitters in light-emitting diodes (LEDs) is extremely attractive for sensing and diagnostics, telecommunications, and biomedical sciences. However, the most efficient NIR LEDs suitable for printable electronics rely on emissive materials containing precious transition metal ions (such as platinum), which have triggered concerns about their poor biocompatibility and sustainability. Here, we review and highlight the latest progress in NIR LEDs based on non-toxic and low-cost functional materials suitable for solution-processing deposition. Different approaches to achieve NIR emission from organic and hybrid materials are discussed, with particular focus on fluorescent and exciplex-forming host-guest systems, thermally activated delayed fluorescent molecules, aggregation-induced emission fluorophores, as well as lead-free perovskites. Alternative strategies leveraging photonic microcavity effects and surface plasmon resonances to enhance the emission of such materials in the NIR are also presented. Finally, an outlook for critical challenges and opportunities of non-toxic NIR LEDs is provided.

Amphiphilic Diazapyrenes with Multiple Stimuli-Responsive Properties

A series of amphiphilic diazapyrenes exhibiting switchable fluorescence under the stimulus of mechanical force or water vapor are reported for the first time. Comprehensive studies of their photophysical properties in different states based on UV-Vis absorption, FL emission, FT-IR spectroscopy, and XRD analysis have revealed a stimuli-induced excimer-based sensing mechanism. The relationship between molecular structures and optical responsive properties of these diazapyrene derivatives is illustrated. Moreover, the unique fluorescent, stimuli-responsive behaviors of these diazapyrene compounds in the solid state are used to fabricate sensory films for successively and orthogonally sensing mechanical force and water vapor. In contrast to the well-established knowledge on the transformation between the pyrene monomer and excimer, our study offers valuable information about the unknown diazapyrene excimers and demonstrates their potential applications in biocompatible force sensors, data storage, and humidity sensors.

Enantiomeric selectivity of ruthenium (II) chiral complexes with antitumor activity, in vitro and in vivo

Different enantiomers of chiral drugs show distinctive activities. Here, a pair of chiral ruthenium Λ-[Ru(phen)₂(TPEPIP)]²⁺ (Λ-Ru), and Δ-[Ru(phen)₂(TPEPIP)]²⁺ (Δ-Ru) (phen = 1,10-phenanthroline; TPEPIP = 2-(4'-(1,2,2-triphenylvinyl)-[1,1'-biphenyl]-4-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) compounds have been prepared and characterized. Both have aggregation-induced emission characteristics, although Λ-Ru exhibits much higher activity, towards duplex DNA extracted from SGC-7901 cancer cells. In vitro experiments demonstrate that both Λ-Ru and Δ-Ru can induce the apoptosis of tumor cells with Λ-Ru showing greater activity than Δ-Ru. Λ-Ru aggregates in the cell nucleus of SGC-7901 within 5 h which shows that nucleic acids may be the effective target of Λ-Ru. In vivo experiments with nude mice showed that Λ-Ru can inhibit the growth and proliferation of a tumor, in tumor-bearing mice as well as targeting the tumor site, as demonstrated by fluorescence. These results demonstrate the dual-function of Λ-Ru, which could be used for real-time visualization of a chemotherapeutic agent.

Fluorescence detection of fluorine ions in biological fluids based on aggregation-induced emission

Traditional chemical and biological sensors developed through aggregation-induced emission (AIE) are mainly based on “Turning on” pattern of fluorescence enhancement, which often has poor selectivity and can be easily interfered with by other substances. On this basis, an AIE-based tetraphenyl ethylene (TPE) derivative (TPE-COOH) was prepared in this study and aggregated by adding Al³⁺, so as to form the TPE-COOH/Al³⁺ polymer. TPE-COOH fluorescence was enhanced through AIE principle, thus realizing the “Turning on” state. F⁻ could bind to Al³⁺ after the addition of F⁻ ions which would result in the decomposition of TPE-COOH/Al³⁺ aggregate, dissolved state of TPE-COOH and gradual reduction of fluorescence intensity of the system, thus realizing “Turning off” state. Moreover, F⁻ ions in biological fluid were analyzed and detected through such AIE-based “Turning on-off” pattern. The linear range of this method for F⁻ detection was 3–12 μM and the detection limit was 0.9 μM.

Schematic diagram of fluorescence detection of F⁻ ions in biological fluids based on TPE-COOH/Al³⁺ polymer Aggregation-Induced Emission (AIE) “Turning on–off” mode.

Pyridinium-Substituted Tetraphenylethylenes Functionalized with Alkyl Chains as Autophagy Modulators for Cancer Therapy

Tuning autophagy in a controlled manner could facilitate cancer therapy but it remains challenging. Pyridinium-substituted tetraphenylethylene salts (PTPE 1-3), able to target mitochondria and disrupt autophagy after forming complexes with albumin, are reported. Mitochondrion affinity and autophagy-inducing activity are improved by prolonging the length of alkyl chains in PTPE 1-3. PTPE 1-3 demonstrate proautophagic activity and a mitophagy blockage effect. Failure of autophagosome-lysosome fusion in downstream autophagy flux results in cancer cell death. Moreover, fast formation of complexes of PTPE 1-3 with albumin in blood can facilitate biomimetic delivery and deep tumor penetration. Efficient tumor accumulation and effective tumor suppression are successfully demonstrated with in vitro and in vivo studies. PTPE 1-3 salts exhibit dual functionality: they target and image mitochondria because of aggregation-induced emission effects and they are promising for cancer therapy.

Coordination-driven self-assembly of discrete supramolecular double-metallacycles

This review comprehensively summarizes the recent advances in the coordination-driven self-assembly of discrete supramolecular double-metallacycles.

Tunable Aggregation-Induced Emission of Imidazole Hydrazones by pH and Anions

Aggregation-induced emission (AIE) materials have drawn great attention for applications as organic light-emitting diodes (OLED) and probes. The applications are, however, restricted by the complex syntheses and hydrophobic properties. Herein, a one-step synthesis of an AIE material based on imidazole hydrazone is assessed. Protonation of the imidazole-H leads to emission color change from yellow to green in the solid state. The emission color is recovered upon imidazole-H⁺ deprotonation. Moreover, the emission wavelength shifts from 532 to 572 nm by anion exchange. In addition, an enhanced emission (Φ_F up to 22.6 %) was obtained with the Br^- anion compared with NTf₂ ^- , SbCl₅ ^- , PF₆ ^- , and OTf^- anions. X-ray crystallography studies together with theoretical calculations show that the enhanced emission of hydrazone salts arises from strong hydrogen bonding between the hydrazone proton and the halide ion (Cl^- or Br^- ).

Identification of Potent Caspase-8 Inhibitors from a Library of Fluorescent Natural Products Screened by an AIEgen-Based Light-Up Probe

Fluorescent natural products are a rich source of drugs and chemical probes, but their innate fluorescence can interfere with fluorescence-based screening assays. Caspase-8 is a key player in apoptosis, its inhibition having been found to be beneficial for treatment of inflammatory and neurodegenerative diseases. Small-molecular inhibitors of caspase-8 remain sparsely reported, however. In this study, we firstly developed a light-up probe based on an AIEgen and capable of targeting caspase-8. This fluorescent dye has a Stokes shift of 200 nm, which could allow the innate fluorescence signals of natural products to be avoided. On screening a library of 86 fluorescent natural products, we found for the first time that gossypol showed potent inhibition of caspase-8 in vitro and in situ. This unique light-up probe, coupled with colored natural products, could represent an efficient approach to hit discovery for druggable targets.

A water-soluble AIE-gen for organic-solvent-free detection and wash-free imaging of Al3+ ions and subsequent sensing of F− ions and DNA tracking

A water-soluble TPE-based AIEgen (TPE-diBuS) was developed for organic-solvent-free detection of Al³⁺ ions and its wash-free cell imaging. The TPE-diBuS-Al ensemble was used for the detection of F⁻ ions and DNA tracking.

Benzothiazole-Based AIEgen with Tunable Excited-State Intramolecular Proton Transfer and Restricted Intramolecular Rotation Processes for Highly Sensitive Physiological pH Sensing

In this work, a benzothiazole-based aggregation-induced emission luminogen (AIEgen) of 2-(5-(4-carboxyphenyl)-2-hydroxyphenyl)benzothiazole (3) was designed and synthesized, which exhibited multifluorescence emissions in different dispersed or aggregated states based on tunable excited-state intramolecular proton transfer (ESIPT) and restricted intramolecular rotation (RIR) processes. 3 was successfully used as a ratiometric fluorescent chemosensor for the detection of pH, which exhibited reversible acid/base-switched yellow/cyan emission transition. More importantly, the pH jump of 3 was very precipitous from 7.0 to 8.0 with a midpoint of 7.5, which was well matched with the physiological pH. This feature makes 3 very suitable for the highly sensitive detection of pH fluctuation in biosamples and neutral water samples. 3 was also successfully used as a ratiometric fluorescence chemosensor for the detection of acidic and basic organic vapors in test papers.

Unveiling the Different Emission Behavior of Polytriazoles Constructed from Pyrazine-Based AIE Monomers by Click Polymerization

Polymers with aggregation-induced emission (AIE) characteristics have aroused tremendous interest because of their potential applications in large-area flexible display and luminescent self-assembling, and as stimuli-responsive and porous materials. However, the design of AIE-active polymers is always not as easy as that of small molecules because their properties are hard to predict. In some cases, the polymers prepared from the AIE-active monomers show the aggregation-caused quenching (ACQ) instead of AIE effect. To understand the structure-property relationship of the polymers constructed from the AIE monomers, in this paper, two pyrazine-containing AIE monomers were utilized to construct luminescent polymers by click polymerization. The photophysical property investigation indicates that the polytriazole containing tetraphenylpyrazine units is AIE-active, whereas that bearing 2,3-dicyano-5,6-diphenylpyrazine units suffers from the ACQ effect. Through systematical investigation, the cause for such difference was unveiled. Thus, this work provides a useful guidance for further design of AIE-active polymers.

Multicolor monitoring of cellular organelles by single wavelength excitation to visualize the mitophagy process

Two AIEgens are designed for tracking mitochondria and lysosomes with different emission colors using single wavelength excitation to visualize the mitophagy process.

Multiplexed cellular organelle imaging using single wavelength excitation is highly desirable for unravelling cellular functions but remains challenging. This requires the design of organelle specific fluorophores with distinct emission but similar absorption. Herein, we present two unique aggregation-induced emission (AIE) probes to track mitochondria and lysosomes simultaneously with emission colors that can be distinguished from that of the nucleus stain Hoechst 33342 upon single wavelength excitation. Compared to conventional organelle stains, the two AIE probes have larger Stokes shifts and higher photostability, which endow them with the capability to monitor bioprocesses, such as mitophagy with strong and sustained fluorescent signals. Moreover, both probes can also stain intracellular organelles in zebrafish larvae with good cell-penetrating capabilities, showing their great potential to monitor bioprocesses in vivo.

Spermine-directed supramolecular self-assembly of water-soluble AIE-active tetraphenylethylene: nanobelt, nanosheet, globular and nanotubular structures

Tetrasulfonate-tetraphenylethylene (Su-TPE) is non-emissive in water and upon addition of a good solvent such as THF (f_THF = 95%) it displays strong fluorescence emission with a quantum yield of 6.33%.

Self-agglomerated crystalline needles harnessing ESIPT and AIEE features for the ‘turn-on’ fluorescence detection of Al3+ ions

We report the synthesis of probe 2 for the fluorescence “turn-on” detection of Al³⁺ ions in CH₃OH.

Macrocycles and cages based on tetraphenylethylene with aggregation-induced emission effect

Syntheses, photophysical properties and applications of macrocycles and cages based on tetraphenylethylene with aggregation-induced emission (AIE) effect.

A sensitive fluorescent probe for alkaline phosphatase and an activity assay based on the aggregation-induced emission effect

A sensitive fluorescent probe (TPEQN-P) was designed and synthesized for detecting alkaline phosphatase and monitoring its enzymatic activity based on the specific aggregation-induced emission effect.

Label-free fluorescence turn-on aptasensor for prostate-specific antigen sensing based on aggregation-induced emission-silica nanospheres

Fluorescent light-up probes based on aggregation-induced emission (AIE)-active molecules have recently attracted great research interest due to the intelligent fluorescence activation mechanism and high sensitivity. In this work, an AIE-silica nanosphere (SiO₂ NP)-based label-free fluorescent aptasensor for the sensitive "turn-on" detection of prostate-specific antigen (PSA) is reported for the first time. The positively charged amino-functionalized SiO₂ NPs were used as efficient nanocapturer to electrostatically adsorb single-stranded PSA aptamer (PA) to form SiO₂ NP-PA nanocomposite as well as adsorb negatively charged tetraphenylethylene derivative 3 (TPE3) to form AIE-SiO₂ NP nanocomposite. The binding of the aptamer to the target PSA could induce a rigid aptamer conformation, resulting in the release of the PA away from the surface of SiO₂ NPs. This made the AIE molecules TPE3 aggregate on the SiO₂ NP surface and emit high fluorescence. With the advantages of simple design and rapid responses, the proposed aptasensor showed high sensitivity and selectivity for PSA with a detection limit of 0.5 ng/mL. The aptasensor was further applied in human serum samples with satisfactory results. Given its versatility, high selectivity, and sensitivity, the proposed method could be extended to other targets by varying the recognition probes. Graphical abstract An AIE-SiO₂ NP-based label-free fluorescent aptasensor for the sensitive "turn-on" detection of PSA is reported for the first time.

Aggregation Induced Emission Fluorogens Light Cells via Microtubules: Accessing the Mechanisms of Intracellular Trafficking of Ionic Substances

Understanding the enrichment and intracellular trafficking of substances is centrally important to the biological systems. Here, employing an amphiphilic molecule (denoted by TPE-11) bearing tetraphenylethene moiety, known for aggregation induced emission property, we demonstrated its localization shifting in Hela cells after prolonged incubation. Through a set of delicately designed experiments, we found that one type of cytoskeleton, i.e., microtubule, is responsible for the intracellular transportation regardless of the sources of fluorogens, via endocytosis pathways or not. As the polymerization of microtubules was blocked, the TPE-11 fluorogens were hindered to move to the inner cytoplasm, but scattered in the cells. On the contrary, blocking the polymerization of microfilament has no such effect. We assume that the dynamic polymerization of microtubules should be responsible to the transportation of TPE-11. More importantly, we found that the interaction between TPE-11 and microtubule proteins also happens during process of polymerization in vitro. The intracellular trafficking of TPE-11 by microtubules may be generalized to other amphiphilic molecules as well as endocytosis pathway, and serves as references in designing functional molecules involved in the intracellular transportation.

Dual-targeted peptide-conjugated multifunctional fluorescent probe with AIEgen for efficient nucleus-specific imaging and long-term tracing of cancer cells

Precisely targeted transportation of a long-term tracing regent to a nucleus with low toxicity is one of the most challenging concerns in revealing cancer cell behaviors. Here, we report a dual-targeted peptide-conjugated multifunctional fluorescent probe (cNGR-CPP-NLS-RGD-PyTPE, TCNTP) with aggregation-induced emission (AIE) characteristic, for efficient nucleus-specific imaging and long-term and low-toxicity tracing of cancer cells. TCNTP mainly consists of two components: one is a functionalized combinatorial peptide (TCNT) containing two targeted peptides (cNGR and RGD), a cell-penetrating peptide (CPP) and a nuclear localization signal (NLS), which can specifically bind to a cell surface and effectively enter into the nucleus; the other one is an AIE-active tetraphenylethene derivative (PyTPE, a typical AIEgen) as fluorescence imaging reagent. In the presence of aminopeptidase N (CD13) and integrin αvβ3, TCNTP can specifically bind to both of them using cNGR and RGD, respectively, lighting up its yellow fluorescence. Because it contains CPP, TCNTP can be effectively integrated into the cytoplasm, and then be delivered into the nucleus with the help of NLS. TCNTP exhibited strong fluorescence in the nucleus of CD13 and integrin αvβ3 overexpression cells due to the specific targeting ability, efficient transport capacity and AIE characteristic in a more crowded space. Furthermore, TCNTP can be applied for long-term tracing in living cells, scarcely affecting normal cells with negligible toxicity in more than ten passages.

Modulating aggregation-induced emission via a non-conjugated linkage of fluorophores to tetraphenylethenes

A fluorophore (DNS or NBD) is attached to tetraphenylethene via a non-conjugated bridge, endowing the resulting aggregates with distinct emission properties.

Synthesis of platinum(ii) complex end functionalized star polymers: luminescence enhancements and unimolecular micelles in solvents of weakened quality

Platinum(ii) complex end functionalized star polymers have been synthesized by reacting K₂PtCl₄ with star ligands ended with 2,6-bis(benzimidazol-2′-yl)pyridine. They show luminescence enhancements and form unimolecular micelles in solvents of weakened quality.

Introductory lecture: recent research progress on aggregation-induced emission

Since the discovery of the aggregation-induced emission (AIE) phenomenon in 2001, research on AIE molecules has drawn much attention, and this area has been expanding tremendously. This brief review will focus on recent advances in the science and application of AIE molecules, including new mechanistic understanding, new AIE molecules for sensing and imaging, stimuli-responsive AIE molecules and applications of AIE molecules for OLEDs. Moreover, this review will give a perspective on the possible opportunities and challenges that exist in the future for this area.

A highly selective fluorescence turn-on detection of ClO−with 1-methyl-1,2-dihydropyridine-2-thione unit modified tetraphenylethylene

A novel fluorescent probe for ClO⁻is developed by the combination of a new ClO⁻responsive unit and the aggregation induced-emission feature of tetraphenylethylene.

Emissive nanoparticles from pyridinium-substituted tetraphenylethylene salts: imaging and selective cytotoxicity towards cancer cells in vitro and in vivo by varying counter anions

Chemotherapeutics specifically targeting cancer cells without damaging healthy cells is the long-awaited goal of cancer treatment. In this paper, a series of nanoparticles (NanoTPES 1-4) assembled from pyridinium-substituted tetraphenylethylene salts were synthesized and investigated both in vitro and in vivo for this purpose. By changing the counter anions, NanoTPES 1-4 exhibit tunable emission colors, sizes and surface charges. NanoTPES 2 and 3 with tetraphenyl borate and tetra(4-chlorophenyl) borate as the respective anions selectively imaged and targeted mitochondria in cancer cells. Accordingly, these two nanoparticles specifically kill cancer cells with minimal effect on normal cells. Such selective cytotoxicity was attributed to the change of membrane potential and inhibition of ATP synthesis in the mitochondria of cancer cells. Furthermore, both NanoTPES 2 and 3 exhibited efficient tumor accumulation and tumor growth inhibition in vivo, with negligible systemic toxicity.

On the Molecular Form of Amyloid Marker, Auramine O, in Human Insulin Fibrils

Designing extrinsic fluorescence sensors for amyloid fibrils is a very active and important area of research. Recently, an ultrafast molecule rotor dye, Auramine O (AuO), has been projected as a fluorescent amyloid marker. It has been claimed that AuO scores better than the most extensively utilized gold-standard amyloid probe, Thioflavin-T (ThT). This advantage arises from the fact that AuO, in addition to its usual emission band (∼500 nm), also displays a large red-shifted emission band (∼560 nm), exclusively in the presence of human insulin fibril medium and not in the native protein or buffer media. On the contrary, for ThT, the emission maximum (∼490 nm) largely remains unchanged while going from protein to fibril. This otherwise unknown large red-shifted emission band of AuO, observed in the presence of human insulin fibrils, was tentatively attributed to a species formed upon fast proton dissociation from excited AuO. It was proposed that because of the long excited-state lifetime (∼1.8 ns) of AuO upon association with human insulin fibrils, this fast proton dissociation from excited AuO could be observed, which is otherwise not observed in buffer or native protein media, owing to its very short excited-state lifetime (∼1 ps). Herein, we show that despite the long excited-state lifetime of AuO in other fibrillar media (human serum albumin and lysozyme), the new red-shifted emission band at 560 nm is not observed, thus possibly suggesting a different origin of the red-shifted emission band of AuO in human insulin fibril medium. We convincingly show that this red-shifted band of AuO (∼560 nm) could be observed under conditions that promote dye aggregation, such as a premicellar concentration of surfactants and polyelectrolytes. These AuO aggregates display strong emission wavelength dependence of transient decay traces, similar to that for AuO in human insulin fibril medium. Detailed time-resolved emission spectral (TRES) measurements suggest that the AuO/premicellar surfactant and AuO/human insulin fibril system share similar features, such as a dynamic red-shift in TRES and an isoemissive point in the time-resolved area-normalized emission spectra, suggesting that the characteristic red-shifted emission band of AuO in human insulin fibril medium may arise from AuO aggregates.

Tuning the Solid State Emission of the Carbazole and Cyano-Substituted Tetraphenylethylene by Co-Crystallization with Solvents

Solid state emissive materials with high quantum yields and tunable emissions are desirable for various applications. A new TPE derivative (1) with two carbazole moieties and two cyano groups is reported, which shows typical aggregation induced emission behavior. Four crystals 1a, 1b, 1c, and 1d are obtained after crystallization from N,N-dimethylformamid (DMF), trichloromethane (CHCl₃ ), tetrahydrofuran (THF), and dichloromethane (CH₂ Cl₂ ), respectively. Crystal structural analyses reveal that (i) molecules of 1 co-crystallize with DMF, CHCl₃ , THF, and CH₂ Cl₂ in 1a, 1b, 1c, and 1d, respectively, and (ii) conformations of 1 are different within 1a, 1b, 1c, and 1d, and compound 1 within crystal 1a adopts the most twisting conformation. Crystalline solids 1a, 1b, 1c, and 1d exhibit high emission quantum yields up to 0.65, but their emission colors are varied from blue to green. In comparison, the amorphous solid of 1 is yellow-emissive with emission maximum at 542 nm. Moreover, the blue- or green-emissive crystalline solids and the yellow-emissive amorphous solid can be inter-converted by the grinding of crystalline solids and exposure of the amorphous solid to vapors of appropriate solvents. It is also demonstrated that microrods of 1a, 1b, and 1d show typical optical waveguiding behavior.

Biocompatible Red Fluorescent Organic Nanoparticles with Tunable Size and Aggregation-Induced Emission for Evaluation of Blood-Brain Barrier Damage

Detection of damage to the blood-brain barrier (BBB) is important for the diagnosis of brain diseases and therapeutic drug evaluation. The widely used probe, Evans blue, suffers from low specificity and high toxicity in vivo. It is shown that organic nanoparticles with tuneable size, good biocompatibility, and aggregation-induced emission characteristics offer high detection specificity to detect BBB damage via a photothrombotic ischemia rat model.