Research on aggregation-induced emission (AIE) has become increasingly popular recently and various AIE luminogens (AIEgens) have been developed based on tetraphenylethene, hexaphenylsilole, distyrylanthracene, tetraphenylpyrazine, etc. However, facile tuning of the AIEgen emissions in a wide range remains challenging. Herein, a novel series of AIEgens is reported, based on imidazole-cored molecular rotors, with facile synthesis and emission colors covering the whole visible spectrum. Moreover, these imidazole derivatives exhibit biological functions unique among the AIEgens, including mitochondria-specific imaging and antifungal activity. Benefiting from the easy preparation and the tunable emission, the imidazole derivatives are expected to not only diversify the family of AIEgens but also enrich their biological applications.

Anionic surfactants are widely used in daily life and industries, but their residues can cause serious damage to the environment. The current detection methods for anionic surfactants suffer from various limitations and a new detection strategy is highly desirable. Based on 2-(2-hydroxyphenyl)benzothiazole fluorogen with aggregation-induced emission characteristics, we have developed a fluorescent probe HBT-C₁₈ for selective and sensitive detection of anionic surfactants. By in situ formation of catanionic aggregates or micelles with anionic surfactants, the emission intensity of the HBT-C₁₈ probe can increase with increasing keto/enol emission ratio through restriction of intramolecular motion and excited-state intramolecular proton-transfer mechanisms. The probe can also be used for wash-free imaging of bacteria enveloped by a negatively charged outer membrane. The results of this study provide a new strategy for sensitive detection of anionic surfactants and wash-free bacterial imaging.

Integrated systems that offer traceable cancer therapy are highly desirable for personalized medicine. Herein, a probe is reported that is composed of a red-emissive photosensitizer (PS) with aggregation-induced emission characteristics and a built-in apoptosis sensor with activatable green emission for targeted cancer cell ablation and real-time monitoring of PS activation and therapeutic response. The probe is nonemissive in aqueous media and can be selectively uptaken by α_vβ₃ integrin overexpressed cancer cells. Cleavage of the probe by intracellular glutathione leads to release of the apoptosis sensor and red fluorescence turn-on to report the PS activation. Upon light irradiation, the PS can generate reactive oxygen species to induce cell apoptosis and activate caspase-3/-7, which will cleave the apoptosis sensor to yield intense green fluorescence. Both the red and green emission can be obtained through a single wavelength excitation, which makes the probe very convenient for therapeutic protocol development.

Multimodal imaging provides complimentary information that is advantageous in studying both cellular and molecular mechanisms in vivo, which has tremendous potential in pre-clinical research and clinical translational imaging. It is desirable to design probes for multimodal imaging that can be administered minimally but provides multifaceted information. Herein, we demonstrate the complementary dual functional ability of a nanoconstruct for molecular imaging in both photoacoustic (PA) and surface-enhanced Raman scattering (SERS) biosensing simultaneously in tandem. To realize this, a group of NIR active organic molecules are designed and synthesized that possess both SERS and PA activity. Nanoconstructs realized by anchoring such molecules onto gold nanoparticles are demonstrated for targeting cancer biomarkers in vivo while providing complimentary information about biodistribution and targeting efficiency. In future, such nanoconstructs could play a major role in identifying surgical margins and also for disease monitoring in translational medicine.

Targeted delivery of drugs toward mitochondria of specific cancer cells dramatically improves therapy efficiencies especially for photodynamic therapy (PDT), as reactive oxygen species (ROS) are short in lifetime and small in radius of action. Different from chemical modification, nanotechnology has been serving as a simple and nonchemical approach to deliver drugs to cells of interest or specific organelles, such as mitochondria, but there have been limited examples of dual-targeted delivery for both cells and mitochondria. Here, cellular and mitochondrial dual-targeted organic dots for image-guided PDT are reported based on a fluorogen with aggregation-induced emission (AIEgen) characteristics. The AIEgen possesses enhanced red fluorescence and efficient ROS production in aggregated states. The AIE dot surfaces are functionalized with folate and triphenylphosphine, which can selectively internalize into folate-receptor (FR) positive cancer cells, and subsequently accumulate at mitochondria. The direct ROS generation at mitochondria sites is found to depolarize mitochondrial membrane, affect cell migration, and lead to cell apoptosis and death with enhanced PDT effects as compared to ROS generated randomly in cytoplasm. This report demonstrates a simple and general nanocarrier approach for cellular and mitochondrial dual-targeted PDT, which opens new opportunities for dual-targeted delivery and therapy.

Intracellular viscosity is a crucial parameter that indicates the functioning of cells. In this work, we demonstrate the utility of TPE-Cy, a cell-permeable dye with aggregation-induced emission (AIE) property, in mapping the viscosity inside live cells. Owing to the AIE characteristics, both the fluorescence intensity and lifetime of this dye are increased along with an increase in viscosity. Fluorescence lifetime imaging of live cells stained with TPE-Cy reveals that the lifetime in lipid droplets is much shorter than that from the general cytoplasmic region. The loose packing of the lipids in a lipid droplet results in low viscosity and thus shorter lifetime of TPE-Cy in this region. It demonstrates that the AIE dye could provide good resolution in intracellular viscosity sensing. This is also the first work in which AIE molecules are applied in fluorescence lifetime imaging and intracellular viscosity sensing.

We present a nitrogen-containing polycyclic aromatic hydrocarbon (N-PAH), namely 12-methoxy-9-(4-methoxyphenyl)-5,8-diphenyl-4-(pyridin-4-yl)pyreno[1,10,9-h,i,j]isoquinoline (c-TPE-ON), which exhibits high quantum-yield emission both in solution (blue) and in the solid state (yellow). This molecule was unexpectedly obtained by a three-fold, highly regioselective photocyclodehydrogenation of a tetraphenylethylene-derived AIEgen. Based on manifold approaches involving UV/Vis, photoluminescence, and NMR spectroscopy as well as HRMS, we propose a reasonable mechanism for the formation of the disk-like N-PAH that is supported by density functional theory calculations. In contrast to most PAHs that are commonly used, our system does not suffer from entire fluorescence quenching in the solid state due to the peripheral aromatic rings preventing π–π stacking interactions, as evidenced by single-crystal X-ray analysis. Moreover, its rod-like microcrystals exhibit excellent optical waveguide properties. Hence, c-TPE-ON comprises a N-PAH with unprecedented luminescent properties and as such is a promising candidate for fabricating organic optoelectronic devices. Our design and synthetic strategy might lead to a more general approach to the preparation of solution- and solid-state luminescent PAHs.

Multiple intramolecular motions consume the excited-state energy of luminogenic molecules upon photoexcitation and lower the emission efficiency. The low frequency rotational motion of aromatic rings can be facilely restricted by steric constraint in the condensed phase, but the high frequency bond stretching motion can hardly be suppressed by aggregation. In this work, three phosphorus-containing heterocycles, 1,2,3,4,5-pentaphenylphosphole-1-oxide (PPPO), 1,2,3-triphenylphosphindole-1-oxide (TPPIO), and 1,2,3-triphenylphosphindole (TPPI), were synthesized and characterized. Their optical properties, crystal-packing manners, electronic features, and fluorescence dynamics were systematically investigated, and theoretical calculations were performed to decipher structure–property relationships. The results reveal that these luminogens are weak emitters in solutions but show strong emission in aggregates, exhibiting obvious aggregation-induced emission (AIE) features. The aggregation-insensitive stretching motion, which is dominant in PPPO, is lowered in TPPIO, enabling TPPIO to fluoresce much more efficiently than PPPO in aggregates. The stretching motion is even more lowered in TPPI, but its relatively planar conformation suffers emission quenching due to strong π–π stacking interactions in aggregates. Therefore, a twisted molecular conformation consisting of a rigid stator and a rotatable periphery is demonstrated to be a rational design for more efficient AIE luminogens.

A novel molecular design strategy is provided to rationally tune the stimuli response of luminescent materials with aggregation-induced emission (AIE) characteristics. A series of new AIE-active molecules (AIE rotors) are prepared by covalently linking different numbers of tetraphenylethene moieties together. Upon gradually increasing the number of rotatable phenyl rings, the sensitivity of the response of the AIE rotors to viscosity and temperature is significantly enhanced. Although the molecular size is further enlarged, the performance is only slightly improved due to slightly increased effective rotors, but with largely increased rotational barriers. Such molecular engineering and experimental results offer more in-depth insight into the AIE mechanism, namely, restriction of intramolecular rotations. Notably, through this rational design, the AIE rotor with the largest molecular size turns out to be the most viscosensitive luminogen with a viscosity factor of up to 0.98.

The facile synthesis of a tetraphenylethene-based macrocycle having aggregation-induced emission characteristics and that expresses illusory topology of the Penrose stairs is presented. As a result of the twisted chirality (P or M) of the tetraphenylethene unit and the axial chirality of the macrocyclic linkage (R or S), the macrocycle exhibits two absolute configurations whose interconversion is energetically favorable as revealed by theoretical calculations.

“United we stand, divided we fall.”–Aesop.

Aggregation-induced emission (AIE) refers to a photophysical phenomenon shown by a group of luminogenic materials that are non-emissive when they are dissolved in good solvents as molecules but become highly luminescent when they are clustered in poor solvents or solid state as aggregates. In this Review we summarize the recent progresses made in the area of AIE research. We conduct mechanistic analyses of the AIE processes, unify the restriction of intramolecular motions (RIM) as the main cause for the AIE effects, and derive RIM-based molecular engineering strategies for the design of new AIE luminogens (AIEgens). Typical examples of the newly developed AIEgens and their high-tech applications as optoelectronic materials, chemical sensors and biomedical probes are presented and discussed.

2,3,4,5-Tetraphenylsiloles are excellent solid-state light emitters featured aggregation-induced emission (AIE) characteristics, but those that can efficiently function as both light-emitting and electron-transporting layers in one organic light-emitting diode (OLED) are much rare. To address this issue, herein, three tailored n-type light emitters comprised of 2,3,4,5-tetraphenylsilole and dimesitylboryl functional groups are designed and synthesized. The new siloles are fully characterized by standard spectroscopic and crystallographic methods with satisfactory results. Their thermal stabilities, electronic structures, photophysical properties, electrochemical behaviors and applications in OLEDs are investigated. These new siloles exhibit AIE characteristics with high emission efficiencies in solid films, and possess lower LUMO energy levels than their parents, 2,3,4,5-tetraphenylsiloles. The double-layer OLEDs [ITO/NPB (60 nm)/silole (60 nm)/LiF (1 nm)/Al (100 nm)] fabricated by adopting the new siloles as both light emitter and electron transporter afford excellent performances, with high electroluminescence efficiencies up to 13.9 cd A^–1, 4.35% and 11.6 lm W^–1, which are increased greatly relative to those attained from the triple-layer devices with an additional electron-transporting layer. These results demonstrate effective access to n-type solid-state emissive materials with practical utility.

In this paper, photoelectric cooperative induced patterned wetting is demonstrated on a hydrophobic ordered polymeric honeycomb structure surface, which is prepared by BF method, then photosensitizing with a dye and hydrophobizing with low-surface-energy materials; finally, photoelectric cooperative induced patterned wetting is achieved on such a hydrophobic honeycomb structure surface. These results indicate that this work is promising for broadening the applications of photoelectric cooperative liquid reprography, which break the limitations of only using inorganic materials and super-hydrophobic materials. It should be of great scientific interest to extend the relevant research from inorganic nanorod, nanopore, and nanotube structures to polymeric honeycomb structures, because polymeric materials can overcome the inherent drawbacks of the inorganic materials owing to their advantages of low specific weight, flexibility, tunable material properties, and wide variety.

Efficient long-term cell tracing in a noninvasive and real-time manner is of great importance to understand genesis, development, invasion, and metastasis of cancerous cells. Cell penetrating organic dots with aggregation- induced emission (AIE) characteristics are successfully developed as long-term cell trackers. The AIE dots enjoy the advantages of high emission efficiency, large Stokes shift, good biocompatibility, and high photostability, which ensure their good performance in long-term non-invasive in vitro cell tracing. Moreover, it is the first report that AIE dots exhibit certain permeability to cellular nucleus, making them attractive potential candidates for nucleus imaging. The AIE dots display superior performance compared to their counterparts of inorganic quantum dots, opening a new avenue in the development of fluorescent probes for monitoring biological processes.

Long-term tracking of bacterial viability is of great importance for monitoring the viability change of bacteria under storage, evaluating disinfection efficiency, as well as for studying the pharmacokinetic and pharmacodynamic properties of antibacterials. Most of the conventional viability dyes, however, suffer from high toxicity and/or poor photostability, making them unsuitable for long-term studies. In this work, an aggregation-induced emission molecule, TPE-2BA, which can differentiate dead and living bacteria and serve as a highly fluorescent and photostable probe for long-term viability assay. TPE-2BA is a cell-impermeable DNA stain that binds to the groove of double-stranded DNA. Bacteria with compromised membrane open the access for TPE-2BA to reach DNA, endowing it with strong emission. The feasibility of using TPE-2BA for screening effective bactericides is also demonstrated. Plate count experiment reveals that TPE-2BA poses negligible toxicity to bacteria, indicating that it is an excellent probe for long-term bacterial viability assay.

In this study, a yellow luminogen (TPE-DCV) was synthesized by treating tetraphenylethene with two dicyanovinyl units. TPE-DCV is non-emissive in solution but becomes a strong emitter when aggregated in poor solvents or in the solid state, thereby displaying a phenomenon of aggregation-induced emission. The solid-state emission of TPE-DCV can be reversibly switched between green and yellow with a moderate contrast ratio by grinding and fuming or heating processes owing to the morphological change between thermodynamically stable crystalline phase and the metastable amorphous state and vice versa. Negligible reabsorption and well-ordered molecular arrangement of the microcrystals of TPE-DCV make them promising as optical waveguide materials with low optical loss.

Dibenzothiophene- and dibenzofuran-functionalized ethanes were synthesized by the McMurry coupling reaction. The luminogens are faintly emissive when molecularly dissolved in good solvents, but emit intensively when aggregated as nanoparticles in poor solvents or fabricated as solid thin films, demonstrating the phenomenon of aggregation-induced emission (AIE). Their organic light-emitting diode (OLED) applications were explored, utilizing the AIE effect. Electroluminescence devices with the configuration of indium tin oxide (ITO)/N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB; 60 nm)/dye (20 nm)/1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (TPBi; 10 nm)/tris(8-hydroxyquinoline)aluminum (Alq₃; 30 nm)/LiF (1 nm)/Al (100 nm) were fabricated. The OLED device emits at 510 nm with a maximum luminescence and external quantum efficiency of 10⁴ cd/m² and 2.1 %, respectively. The OLED behavior of the E/Z isomers was also studied.

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).

In this paper, a simple strategy to change the emission behaviour of luminogenic materials was developed. Tetraphenylethene (TPE)-functionalised benzothiazolium salts with different counteranions (TPEBeX; X=I⁻, ClO₄⁻ and PF₆⁻) were designed and synthesised. All the luminogens show weak red emission in the solution state that originates from intramolecular charge transfer from TPE to the benzothiazolium unit. Whereas aggregate formation enhances the light emission of TPEBeClO₄ and TPEBePF₆, that of TPEBeI is quenched, thus demonstrating the phenomena of aggregation-induced emission and aggregation-caused quenching. TPEBeI works as a light-up fluorescent sensor for Hg²⁺ in aqueous solution with high sensitivity and specificity owing to the elimination of the emission quenching effect of the iodide ion by the formation of HgI₂ as well as the induction in aggregate formation by the complexation of Hg²⁺ with the S atom of the benzothiazolium unit of TPEBeI. A solid film of TPEBeI was prepared that can monitor the level of Hg²⁺ in aqueous solution with a detection limit of 1 μM.

2,3,4,5-Tetraarylsiloles are a class of important luminogenic materials with efficient solid-state emission and excellent electron-transport capacity. However, those exhibiting outstanding electroluminescence properties are still rare. In this work, bulky 9,9-dimethylfluorenyl, 9,9-diphenylfluorenyl, and 9,9′-spirobifluorenyl substituents were introduced into the 2,5-positions of silole rings. The resulting 2,5-difluorenyl-substituted siloles are thermally stable and have low-lying LUMO energy levels. Crystallographic analysis revealed that intramolecular π–π interactions are prone to form between 9,9′-spirobifluorene units and phenyl rings at the 3,4-positions of the silole ring. In the solution state, these new siloles show weak blue and green emission bands, arising from the fluorenyl groups and silole rings with a certain extension of π conjugation, respectively. With increasing substituent volume, intramolecular rotation is decreased, and thus the emissions of the present siloles gradually improved and they showed higher fluorescence quantum yields (Φ_F=2.5–5.4 %) than 2,3,4,5-tetraphenylsiloles. They are highly emissive in solid films, with dominant green to yellow emissions and good solid-state Φ_F values (75–88 %). Efficient organic light-emitting diodes were fabricated by adopting them as host emitters and gave high luminance, current efficiency, and power efficiency of up to 44 100 cd m⁻², 18.3 cd A⁻¹, and 15.7 lm W⁻¹, respectively. Notably, a maximum external quantum efficiency of 5.5 % was achieved in an optimized device.

An in-depth understanding of dynamic interfacial self-assembly processes is essential for a wide range of topics in theoretical physics, materials design, and biomedical research. However, direct monitoring of such processes is hampered by the poor imaging contrast of a thin interfacial layer. We report in situ imaging technology capable of selectively highlighting self-assembly at the phase boundary in real time by employing the unique photophysical properties of aggregation-induced emission. Its application to the study of breath-figure formation, an immensely useful yet poorly understood phenomenon, provided a mechanistic model supported by direct visualization of all main steps and fully corroborated by simulation and theoretical analysis. This platform is expected to advance the understanding of the dynamic phase-transition phenomena, offer insights into interfacial biological processes, and guide development of novel self-assembly technologies.

A tetraphenylethene (TPE) derivative substituted with the electron-acceptor 1,3-indandione (IND) group was designed and prepared. The targeted IND-TPE reserves the intrinsic aggregation-induced emission (AIE) property of the TPE moiety. Meanwhile, owing to the decorated IND moiety, IND-TPE demonstrates intramolecular charge-transfer process and pronounced solvatochromic behavior. When the solvent is changed from apolar toluene to highly polar acetonitrile, the emission peak redshifts from 543 to 597 nm. IND-TPE solid samples show an evident mechanochromic process. Grinding of the as-prepared powder sample induces a redshift of emission from green (peak at 515 nm) to orange (peak at 570 nm). The mechanochromic process is reversible in multiple grinding–thermal annealing and grinding–solvent-fuming cycles, and the emission of the solid sample switches between orange (ground) and yellow (thermal/solvent-fuming-treated) colors. The mechanochromism is ascribed to the phase transition between amorphous and crystalline states. IND-TPE undergoes a hydrolysis reaction in basic aqueous solution, thus the red-orange emission can be quenched by OH⁻ or other species that can induce the generation of sufficient OH⁻. Accordingly, IND-TPE has been used to discriminatively detect arginine and lysine from other amino acids, due to their basic nature. The experimental data are satisfactory. Moreover, the hydrolyzation product of IND-TPE is weakly emissive in the resultant mixture but becomes highly blue-emissive after the illumination for a period by UV light. Thus IND-TPE can be used as a dual-responsive fluorescent probe, which may extend the application of TPE-based molecular probes in chemical and biological categories.

Acetylenic polymers are a group of specialty materials with novel properties. In this paper, recent progress in the development of functional acetylenic polymers is summarized. These polymers are synthesized through different polymerization approaches such as Sonogashira polycoupling, decarbonylative chloroarylation polyaddition, and polycyclotrimerization. Efforts in the development of new monomers and catalyst exploration as well as reaction optimization have lead to a large quantity of linear and hyperbranched polymers with high molecular weights and good processability. The polymer functionalization is realized by incorporating functional units into the monomer structures, which endow the resulting polymers with fascinating properties such as aggregation-induced emission, optical nonlinearity, light refractivity, photosensitivity, photopatternability, redoxactivity, and magnetism.

A tetraphenylethene-containing A₄-type tetrayne, named 1,1,2,2-tetrakis(4-ethynylphenyl)ethene is synthesized and its TaCl₅-Ph₄Sn catalyzed homopolycyclotrimerization affords hyperbranched poly(tetraphenylethene) with high molecular weight (M_w = 280,000) in high yield (97%). The polymer shows good solubility and high thermal stability. It is aggregation-enhanced emission (AEE)-active and functions as a fluorescent chemosensor for explosive detection with a superamplification effect and large quenching constants up to 758,000 M⁻¹. The polymer shows high and tunable refractive indices (RI = 1.9288−1.6746) in a wide wavelength region. Porous fluorescent polymer thin film is prepared by breath figure (BF) methods and real-time monitoring of the elusive BF formation process is realized. Photolithography of the thin films readily generates well-resolved fluorescent photopattern without and with porous secondary structure. The polymer is metallified and pyrolysed to give magnetic ceramics with high magnetic susceptibilities (M_s = 83 emu/g) and near-zero coercivity (H_c = 0.08 kOe). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4752–4764

Conjugated polyelectrolytes are promising candidates for the construction of fluorescent bioprobes. In this study, a series of water-soluble fluorescent polyelectrolytes have been designed and synthesized by means of the quaternization of their tetraphenylethene-containing polyyne precursors. The polyynes can be facilely prepared through Hay–Glaser polycoupling in high yields (up to 99 %) with high molecular weights (up to 38 900). All the polymers exhibit a phenomenon of aggregation-induced or -enhanced emission. The fluorimetric titrations of biomolecules such as heparin, calf thymus DNA, RNA, bovine serum albumin, and human serum albumin to buffer solutions of the polyelectrolytes suggest that they are promising fluorescent bioprobes with high sensitivity and fast response. The emission intensity of the polyelectrolytes is enhanced by up to sevenfold upon binding with biomolecules through electrostatic and hydrophobic cooperative interactions. The polyelectrolytes can also serve as fluorescent visualizers for intracellular imaging with good biocompatibility and low autofluorescence interference.

A series of nonplanar tetraphenylethene (TPE)–hexaphenylbenzene (HPB) adducts was designed and synthesized by Diels–Alder reaction of the acetylene precursors and tetraphenylcyclopentadienone. All of the adducts showed aggregation-induced emission features. The twisting amplitude and steric hindrance of the TPE and HPB units were found to play a crucial role in their fluorescence behaviors in the aggregated state.

We demonstrate a concept-proof work of using fluorescence (FL) “turn-on” probes for the discriminatory detection of cysteine (Cys) over homocysteine (Hcy). The fluorogens are provided with aggregation-induced emission (AIE) characteristic and functionalized with two aldehyde-groups (DMTPS-ALD and TPE-ALD). All the detections were carried out in a biocompatible medium (10 mM HEPES buffer and DMSO, pH 7.4). In principle, the formation of thiazinane/thiazolidine through the chemical reaction of aldehydes on the probe molecules and the residue of Cys/Hcy determines the selective recognition of Cys and Hcy over other amino acids and glucose. The FL responses originate from the AIE property of thiazinane/thiazolidine resultants, which have low solubility and precipitate (aggregate) in the detection medium. The discrimination between Cys and Hcy comes from the difference in reaction kinetics of TPE-ALD/DMTPS-ALD with Cys and Hcy, thereby the FL responses show different time courses and intensity enhancement. It is worth noting that TPE-ALD outshined the other two probes in performance with fast response, a high FL enhancement up to 16-fold, high sensitivity, and good specificity and selectivity. Moreover, its FL response threshold at 250 μM is very close to the lower limit of the normal level of Cys in human plasma, which implies that TPE-ALD could be applied as a potential indicator of Cys deficiency.

The detection of nucleic acids, such as DNA and RNA, plays a significant role in genetic engineering, forensics, and bioinformatics. Traditional nucleic acid probes are mainly intercalators, which are potential mutagens, or groove binders that show high preference only for double-stranded DNA. We herein present two versatile fluorescent probes for nucleic acid detection and visualization. The nonemissive tetraphenylethene derivatives (TTAPE) are induced by DNA/RNA to emit, thereby showing a novel phenomenon of aggregation-induced emission (AIE). This kind of “light-up” property enables the quantitation and visualization of nucleic acids in aqueous solution and electrophoretic gels, respectively. The cationic TTAPE can penetrate cells with a compromised plasma membrane easily but cannot enter live cells with an intact membrane, thus making them useful for the differentiation between dead and live cells. On account of the high binding affinity to DNA, TTAPE can selectively label the chromosomes and nuclei in fixed cells, which provides a simple and fast method for the observation of cell mitosis. Owing to their AIE characteristics, the dye molecules aggregate in DNA-rich regions and exert appreciable quantum efficiency as well as superior photostability.

Light emission of 2-(2,6-bis((E)-4-(diphenylamino)styryl)-4H-pyran-4-ylidene)malononitrile (TPA-DCM) is weakened by aggregate formation. Attaching tetraphenylethene (TPE) units as terminals to TPA-DCM dramatically changes its emission behavior: the resulting fluorogen, 2-(2,6-bis((E)-4-(phenyl(4′-(1,2,2-triphenylvinyl)-[1,1′-biphenyl]-4-yl)amino)styryl)-4H-pyran-4-ylidene)malononitrile (TPE-TPA-DCM), is more emissive in the aggregate state, showing the novel phenomenon of aggregation-induced emission (AIE). Formulation of TPE-TPA-DCM using bovine serum albumin (BSA) as the polymer matrix yields uniformly sized protein nanoparticles (NPs) with high brightness and low cytotoxicity. Applications of the fluorogen-loaded BSA NPs for in vitro and in vivo far-red/near-infrared (FR/NIR) bioimaging are successfully demonstrated using MCF-7 breast-cancer cells and a murine hepatoma-22 (H₂₂)-tumor-bearing mouse model, respectively. The AIE-active fluorogen-loaded BSA NPs show an excellent cancer cell uptake and a prominent tumor-targeting ability in vivo due to the enhanced permeability and retention effect.

Benzene-cored luminogens with multiple triarylvinyl units are designed and synthesized. These propeller-shaped molecules are nonemissive when dissolved in good solvents, but become highly emissive when aggregated in poor solvents or in the solid state, showing the novel phenomenon of aggregation-induced emission. Restriction of intramolecular motion is identified as the main cause for this effect. Thanks to their high solid-state fluorescence quantum yields (up to unity) and high thermal and morphological stabilities, light-emitting diodes with the luminogens as emitters give sky-blue to greenish-blue light in high luminance and efficiencies of 10800 cd m⁻², 5.8 cd A⁻¹, and 2.7%, respectively. The emissions of the nanoaggregates of the luminogens can be quenched exponentially by picric acid, or selectively by Ru³⁺, with quenching constants up to 10⁵ and ∼2.0 × 10⁵ L mol⁻¹, respectively, making them highly sensitive (and selective) chemosensors for explosives and metal ions.

The 1,3-dipolar cycloaddition of azides and active internal alkynes has been well studied, but is rarely utilized as a tool for polymer preparation. In this work, an efficient polymerization route is developed. Polycycloaddition of diazide (4) and bis(benzoylethynyl)-benzenes and -butane (3) at elevated temperature has produced the first examples of soluble 1,4,5-trisubstituted polytriazoles PI with satisfactory molecular weights (M_w up to 16 400) in excellent yields (up to 98.6%). All the obtained polymers are thermally stable, losing merely 5% of their weights at temperatures higher than 367 °C. They exhibit higher refractive indices than some commercial plastics and can be crosslinked upon UV irradiation to generate a 3D photopattern with high resolution. The metal-free feature of such a methodology offers a facile tool to prepare functional materials free from the contamination of metal species.

A 3-silolene derivative, 2,2,5,5-tetrakis(dimethylsilyl)-1,1-dimethyl-3,4-diphenyl-3-silolene (TDMSHS), is first synthesized and characterized by X-ray diffraction crystallography and spectroscopic methods. Hydrosilylation polymerization of TDMSHS with 1,1-dimethyl-2,5-bis(4-ethynylphenyl)-3,4-diphenylsilole in the presence of Karstedt's catalyst generates a stereoregular silole-containing hyperbranched poly(silylenevinylene) (hb-SPSV) with a high molecular weight ( = 146 000, / = 1.5) in high yield (≈95%). hb-SPSV exhibits excellent thermal stability and strong fluorescence, and the emission of its aggregates in aqueous mixture can be quenched efficiently by picric acid with large quenching constants K_SV up to 414400 M⁻¹.

A facile route for the synthesis of luminescent and light refractive polymers is proposed. Silole-containing diyne and halogenated tetraphenylethene derivatives are synthesized and their coupling reactions furnish poly(arylene ethynylene)s with high molecular weights in high yields. All of the polymers are soluble and film-forming and possess a high thermal stability. They emit strong green lights when their solutions and nanoparticle suspensions are photoexcited. The polymers show high refractive indices with low chromatic dispersions. Their RI values can be modulated and their thin films can be crosslinked using UV irradiation, generating negative photoresist patterns.

Hydrosilylation polymerizations of 1,1-dimethyl-2,5-bis(4-ethynylphenyl)-3,4-diphenylsilole with aromatic silylhydrides including 1,4-bis(dimethylsilyl)benzene, 4,4′-bis(dimethylsilyl)biphenyl, 2,5-bis(dimethylsilyl)thiophene, and 2,7-bis(dimethylsilyl)-9,9-dihexylfluorene in the presence of Rh(PPh₃)₃Cl catalyst in refluxed tetrahydrofuran afford a series of silole-containing poly(silylenevinylene)s. Under optimum condition, the alkyne polyhydrosilylation reactions progress efficiently and regioselectively, yielding polymers with high molecular weights (M_w up to 95,300) and good stereoregularity (E content close to 99%) in high yields (up to 92%). The polymers are processable and thermally stable, with high decomposition temperatures in the range of 420−449 °C corresponding to 5% weight loss. They are weakly fluorescent in the solution state but become emissive in the aggregate and film states, demonstrating their aggregation-enhanced emission characteristics. The explosive sensing capabilities of the polymers are examined in both solution and aggregate states. The emissions of the polymers aggregates in aqueous mixture are quenched more efficiently by picric acid in an exponential pattern with high quenching constants (up to 27,949 L mol⁻¹), suggesting that the polymers aggregates are sensitive chemosensors for explosive detection. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

A facile approach to thermally stable and efficient solid-state emitters is proposed. By hooking up tetraphenylethene (TPE) units through aryl linkers under Suzuki coupling conditions, a series of arylene bis(tetraphenylethene)s (TPE-Ar-TPE Ar=2,5-dimethyl-1,4-phenylene, 2,5-bis(hexyloxyl)-1,4-phenylene, 1,5-naphthylene, and 9,10-anthracenylene) are prepared in satisfactory to high yields (67–96 %). These molecules are nonluminescent when dissolved in solutions but become highly emissive when aggregated in poor solvents or fabricated as thin film in the solid state, displaying a phenomenon of aggregation-induced emission. Fluorescence quantum yields of 100 % were achieved in the amorphous films of the luminogens. The luminogens exhibit mechano-, vapo-, and thermochromism: their emissions can be repeatedly switched between blue and blue-green colors by simple grinding-fuming and grinding-heating cycles owing to the morphological change from a crystalline to an amorphous state and vice versa. These compounds are thermally stable, losing little of their weight at high temperatures of 421–452 °C. All the luminogens are morphological stable with high glass transition temperatures. Multilayer light-emitting diodes with a device configuration of ITO/NPB/dye/TPBi/Alq₃/LiF/Al are fabricated, which emit sky-blue electroluminescence with maximum luminance and external quantum efficiency of 7900 cd m⁻² and 2.1 %, respectively.

By employing a new synthetic strategy, a series of oligomers and a polymer composed of different number of tetraphenylethene and triphenylamine units was designed and synthesised. The optical physics properties and electroluminescence behaviours were studied comparatively. All the molecules demonstrate an aggregation-induced emission (AIE) phenomenon and bear very high quantum yields in the solid state. The emission wavelengths and quantum efficiencies alternate with the change of the molecular configurations and achieve their maximum at the largest oligomer. The thermal stabilities also become higher along with the increase in the molecular weight. The molecules have suitable HOMO levels that match the work function of the indium tin oxide (ITO) anode. They can act as both light-emitting and hole-transporting materials in OLEDs. Thus the present strategy combines the intrinsic emissive nature of AIE materials and the good hole-transport capability of aromatic amines, thereby achieving a win–win for both optical and electrical properties.

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.

Triphenylamine (TPA)-based conjugated hyperbranched poly(aryleneethynylene)s (PAEs), hb-P1/2, hb-P1/3, and hb-P1/4, were synthesized with high molecular weights and good solubilities through Sonogashira coupling reactions. These PAEs exhibited outstanding thermal stabilities and different emission behaviors. Tetraphenylethene (TPE)-containing hb-P1/2 fluoresced faintly in THF, although its light emission was enhanced by aggregate formation in aqueous media or in thin films, thereby exhibiting an aggregation-induced emission-enhancement (AIEE) effect. Whereas 1,1,2,3,4,5-hexaphenylsilole (HPS)-bearing hb-P1/3 showed no significant change in emission intensity with increasing water content in aqueous media, hb-P1/4, which consisted of TPA–fluorenone donor–acceptor groups, presented almost identical absorptions, but both positive and negative solvatochromic emissions in various solvents. A superquenching effect was observed in the picric-acid-detection process by using nanosuspensions of hb-P1/2. All of the polymers possessed good film formability. UV irradiation of the thin films induced simultaneous photobleaching and cross-linking, thus making them applicable in the fabrication of 2D and 3D patterns. Furthermore, the polymer films also showed high refractive indices, which were tunable upon exposure to UV light.

Polycyclic aromatic hydrocarbons (PAHs) normally exhibit efficient fluorescence in dilute solutions, whereas their emission is significantly quenched in the aggregated state due to the formation of π-aggregates/excimers. The rigid and planar structure of PAHs plays a positive role in terms of fluorescence in solution but a negative one in the aggregated state. To bestow PAHs a luminescent ability in the solid state, we constructed a non-coplanar PAH-substituted ethene. By using the planar PAH fluoranthene as a building block, a highly efficient solid-state emitter with a fluorescence quantum efficiency of unity in the aggregated state was obtained. OLEDs with contain the molecule as an emitter reach a luminance up to 20 520 cd m⁻² and an efficiency of 10 cd A⁻¹.

Nanoparticles with both efficient light emission and strong magnetization (MFSNPs) are fabricated by one-pot, surfactant-free sol–gel reaction of tetraethoxysilane and silole-functionalized siloxane in the presence of citrate-coated magnetite nanoparticles. The MFSNPs are uniformly sized with smooth surfaces. They possess core–shell structures and exhibit appreciable surface charges and hence good colloidal stability. The MFSNPs are superparamagnetic, exhibiting no hysteresis at room temperature. UV irradiation of the suspension of MFSNPs in ethanol gives strong green emission at 486 nm, thanks to the novel aggregation-induced emission characteristics of the silole aggregates in the hybrid nanoparticles. The MFSNPs can selectively stain the cytoplasmic regions of the living cells. Addition of (3-aminopropyl)triethoxysilane during the fabrication of MFSNPs has generated MFSNP-NH₂ with numerous amino groups decorated on the surface, enabling the nanoparticles to immobilize bovine serum albumin efficiently.

2,5-Bis(triphenylsilylethynyl)-3,4-diphenylsiloles with different 1,1-substituents [XYSi(CPh)₂(CCCSiPh₃)₂] (Ph=phenyl) were synthesized in high yields by the Sonogashira coupling of 2,5-dibromo-3,4-diphenylsiloles with triphenylsilylacetylene, and two of these were characterized crystallographically. Crystal structures and theoretical calculations showed that the new silole molecules had higher conjugation than 2,5-diarylsiloles. They possessed low HOMO and LUMO energy levels due to the electron-withdrawing effect of the triphenylsilylethynyl groups. Cyclic voltammetry analysis revealed low electron affinities, which were comparable to those of perfluoroarylsiloles. B3LYP/6-31* calculations demonstrated that the new siloles possessed large reorganization energies for electron and hole transfers and high electron mobilities. A mobility of up to 1.2×10⁻⁵ cm² V⁻¹ s⁻¹ was obtained by the transient electroluminescence method, which was about fivefold higher than that of tris(8-hydroxyquinolinato)aluminum_, a widely used electron-transport material, under the same conditions. All of the silole molecules possessed high thermal stability. Although, their solutions were weakly emissive, their nanoparticle suspensions and thin films emitted intense blue-green light upon photoexcitation, demonstrating a novel feature of aggregation-induced emission (AIE). Polarized emissions were observed in the silole crystals. The addition of solvents, which did not dissolve the silole molecules, into silole-containing solutions caused self-assembly of the molecules, which produced macroscopic fibrils with strong light emissions.

Ferrocene-functionalized disubstituted polyacetylenes are synthesized in high yields by copper-catalyzed click reactions of azido-decorated poly(1-phenyl-1-hexyne) and poly(diphenylacetylene) with 1-ethynylferrocene. All the organometallic polymers are soluble and film-forming. They enjoy high thermal stability (≥300 °C) and are redox-active. Thanks to the ferrocenyl units, thin films of the polymers show high refractive indices (n=1.745–1.698) in the wavelength region of 400–1700 nm as well as high Abbé numbers (v_D’ up to 426) and low optical dispersions (D’ down to 0.002) at telecommunication important wavelengths. Pyrolyses of the polymers under nitrogen furnish magnetic ceramics with high magnetizabilities.

A new synthetic route to sulfur-rich polymers has been developed. The alkyne polyhydrothiolations of 4,4′-thiodibenzenethiol (1) and arylene dipropiolates (2–5) mediated by amines proceed at room temperature in a regioselective fashion, furnishing sole anti-Markovnikov products of poly(vinylenesulfide)s (P1/2–P1/5) with high molecular weights (M_w up to 32 300) and high stereoregularities (Z content up to 81.4%) in high yields (up to 98.2%). Polymers P1/2–P1/4 are soluble in common organic solvents. They are optically transparent, allowing almost all visible and IR light to transmit through. Thanks to the high sulfur contents of the polymers, their films show high refractive indices (n = 1.73–1.70) in the wavelength region of 500–1700 nm as well as high Abbé numbers (ν_D' up to 539) and low optical dispersions (D' down to 0.002) at wavelengths important for telecommunications. Their refractivities can be further enhanced (n up to 2.06) by metal complexation and their films can be crosslinked by UV irradiation, which enables ready fabrication of fluorescent photopatterns.

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

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.

Highly emissive inorganic–organic nanoparticles with core–shell structures are fabricated by a one-pot, surfactant-free hybridization process. The surfactant-free sol–gel reactions of tetraphenylethene- (TPE) and silole-functionalized siloxanes followed by reactions with tetraethoxysilane afford fluorescent silica nanoparticles FSNP-1 and FSNP-2, respectively. The FSNPs are uniformly sized, surface-charged and colloidally stable. The diameters of the FSNPs are tunable in the range of 45–295 nm by changing the reaction conditions. Whereas their TPE and silole precursors are non-emissive, the FSNPs strongly emit in the visible vision, as a result of the novel aggregation-induced emission (AIE) characteristics of the TPE and silole aggregates in the hybrid nanoparticles. The FSNPs pose no toxicity to living cells and can be utilized to selectively image cytoplasm of HeLa cells.

The synthesis of functionalized siloles has been a challenge because of the incompatibility of polar functional groups with the reactive intermediates in the conventional protocols for silole synthesis. In this work, a synthetic route for silole functionalization is elaborated, through which a series of functionalized siloles are successfully prepared. Whereas light emissions of traditional luminophores are often quenched by aggregation, most of the functionalized siloles show an exactly opposite phenomenon of aggregation-induced emission (AIE). The siloles are nonemissive when dissolved in their good solvents but become highly luminescent when aggregated in their poor solvents or in the solid state. Manipulation of the aggregation–deaggregation processes of the siloles enables them to play two seemly antagonistic roles and work as both excellent quenchers and efficient emitters. The AIE effect endows the siloles with multifaceted functionalities, including fluorescence quenching, pH sensing, explosive detection, and biological probing. The sensing processes are very sensitive (with detection limit down to 0.1 ppm) and highly selective (with capability of discriminating among different kinds of ions, explosives, proteins, DNAs, and RNAs). The siloles also serve as active layers in the fabrication of electroluminescent devices and as photosensitive films in the generation of fluorescence patterns.

Regioselective 1,3-dipolar polycycloadditions of tetraphenylethene (TPE)-containing diazides 1–3 and bis(aroylacetylene) 4 are initiated by simple heating, affording poly(aroyltriazole)s (PATAs) PI–PIII with high molecular weights in high yields. The PATAs are completely soluble in common organic solvents and stable at temperatures up to 358 °C. Thanks to their TPE units, the polymers show aggregation-induced emission and work as explosive sensors with high sensitivity. The PATAs are optically transparent in the whole visible spectral region. Their refractive indexes can be tuned to a great extent (Δn ≈ 0.08) by simply changing their alkyl spacer lengths. The modified Abbé numbers of the PATAs are very high (up to 273), indicative of very low optical dispersions in the telecommunication-important wavelength region. UV irradiation through a photomask quenches the light emissions of the polymers, enabling the generation of two-dimensional fluorescent images without development. The polymers can be readily photo-crosslinked, yielding three-dimensional patterns with high resolutions.

Biosensing processes such as molecular beacons require non-trivial effort to covalently label or mark biomolecules. We report here a label-free DNA assay system with a simple dye with aggregation-induced emission (AIE) characteristics as the fluorescent bioprobe. 1,1,2,2-Tetrakis[4-(2-bromoethoxy)phenyl]ethene is nonemissive in solution but becomes highly emissive when aggregated. This AIE effect is caused by restriction of intramolecular rotation, as verified by a large increase in the emission intensity by increasing viscosity and decreasing temperature of the aqueous buffer solution of 1,1,2,2-tetrakis[4-(2-triethylammonioethoxy)phenyl]ethene tetrabromide (TTAPE). When TTAPE is bound to a guanine-rich DNA strand (G1) via electrostatic attraction, its intramolecular rotation is restricted and its emission is turned on. When a competitive cation is added to the G1 solution, TTAPE is detached and its emission is turned off. TTAPE works as a sensitive poststaining agent for poly(acrylamide) gel electrophoresis (PAGE) visualization of G1. The dye is highly affinitive to a secondary structure of G1 called the G-quadruplex. The bathochromic shift involved in the G1 folding process allows spectral discrimination of the G-quadruplex from other DNA structures. The strong affinity of TTAPE dye to the G-quadruplex structure is associated with a geometric fit aided by the electrostatic attraction. The distinct AIE feature of TTAPE enables real-time monitoring of folding process of G1 in the absence of any pre-attached fluorogenic labels on the DNA strand. TTAPE can be used as a K⁺ ion biosensor because of its specificity to K⁺-induced and -stabilized quadruplex structure.

Perylene (Py)-containing polyacetylenes with different skeleton structures [HCC(C₆H₄)CO₂Py]_n (P1), [HCC(CH₂)₈CO₂Py]_n (P2), and {[(C₆H₅) CC(CH₂)₉NH₂]co[(C₆H₅)CC(CH₂)₉Py]}_n (P3) are synthesized in satisfactory yields by Rh-catalyzed polymerization (for P1 and P2) and polymer reaction (for P3). All the polymers are soluble and possess high molecular weights (M_w up to 2.8 × 10⁵). Their structures and properties are characterized and evaluated by IR, NMR, UV, TGA, PL, and photovoltaic (PV) analyses. The polymers are thermally stable, losing little of their weights when heated to 330 °C. When their solutions are irradiated, their perylene pendants emit intense red fluorescence at 610 nm. PV cells with a configuration of ITO/PEDOT:PSS/polymer/LiF/Al are fabricated, which show maximum current density of 10.3 μA/cm². The external quantum efficiency is sensitive to the polymer structure, with P3 exhibiting the highest value of 0.23%. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2025–2037, 2008