Aggregation‐Induced Dual‐Phosphorescence from Organic Molecules for Nondoped Light‐Emitting Diodes

Aggregation‐induced emission (AIE) is a beneficial strategy for generating highly effective solid‐state molecular luminescence without suffering losses in quantum yield. However, the majority of reported AIE‐active molecules exhibit only strong fluorescence, which is not ideal for electrical excitation in organic light‐emitting diodes (OLEDs). By introducing various substituent groups onto the biscarbazole compound, a series of molecular materials with aggregation‐induced phosphorescence (AIP) is designed, which exhibits two distinctly different phosphorescence bands and an absolute solid‐state room‐temperature phosphorescence quantum yield up to 64%. Taking advantage of the AIE feature, the AIP molecules are fabricated into OLEDs as a homogeneous light‐emitting layer, which allows for relatively small efficiency roll‐off and shows an external electroluminescence quantum yield of up to 5.8%, more than the theoretical limit for purely fluorescent OLED devices. The design showcases a promising strategy for the production of cost‐effective and highly efficient OLED technology.     

Efficient Aggregation‐Induced Emission Manipulated by Polymer Host Materials

Linear copolymer hosts bearing a number of pillar[5]arene dangling side chains are synthesized for the facile construction of highly emissive supramolecular polymer networks (SPNs) upon noncovalently cross‐linking with a series of tetraphenyethylene (TPE)‐based tetratopic guests terminated with different functional groups through supramolecular host–guest interactions. An extremely high fluorescence quantum yield (98.22%) of the SPNs materials is obtained in tetrahydrofuran (THF) by fine‐tuning the parameters, and meanwhile supramolecular light‐harvesting systems based on spherical supramolecular nanoparticles are constructed by interweaving 9,10‐distyrylanthracene (DSA) and TPE‐based guest molecules of aggregation‐induced emission (AIE) with the copolymer hosts in the mixed solvent of THF/H₂O. The present study not only illustrates the restriction of the intramolecular rotations (RIR)‐ruled emission enhancement mechanism regulated particularly by macrocyclic arene‐containing copolymer hosts, but also suggests a new self‐assembly approach to construct high‐performance light‐harvesting materials.     

Facile Access to Twisted Intramolecular Charge‐Transfer Fluorogens Bearing Highly Pretwisted Donor–Acceptor Systems Together with Readily Fine‐Tuned Charge‐Transfer Characters

Twisted intramolecular charge‐transfer (TICT) fluorogens bearing highly pretwisted geometries and readily‐fine‐tuned charge‐transfer characters are quite promising sensor and electroluminescence (EL) materials. In this study, by using 4‐aryloxy‐1,8‐naphthalimide derivatives as the molecular framework, it is demonstrated for the first time that a C? O bond could serve as the central bond to construct new TICT D‐A systems. Photophysical and quantum chemical studies confirm that rotation around central C? O bonds is responsible for the formation of a stable TICT state in these compounds. More importantly, owing to the structural adjustability of the aryl moiety and the strong steric interactions between the naphthalimide and the aryl ring systems, these compounds can display readily‐fine‐tuned TICT characters, hence exhibiting an adjustable solvent polarity threshold for aggregation‐induced emission (AIE) activity, and could be AIE‐active even in less‐polar toluene and nonpolar cyclohexane. Furthermore, these compounds could possess highly‐pretwisted ground‐state geometries, hence could show good EL performance. The findings reveal a facile but effective molecular constructive strategy for versatile, high‐performance optoelectronic TICT compounds.     

Multiscale Humidity Visualization by Environmentally Sensitive Fluorescent Molecular Rotors

Building humidity sensors possessing the features of diverse‐configuration compatibility, and capability of measurement of spatial and temporal humidity gradients is of great interest for highly integrated electronics and wearable monitoring systems. Herein, a visual sensing approach based on fluorescent imaging is presented, by assembling aggregation‐induced‐emission (AIE)‐active molecular rotors into a moisture‐captured network; the resulting AIE humidity sensors are compatible with diverse applications, having tunable geometries and desirable architectures. The invisible information of relative humidity (RH) is transformed into different fluorescence colors that enable direct observation by the naked eyes based on the twisted intramolecular charge‐transfer effect of the AIE‐active molecular rotors. The resulting AIE humidity sensors show excellent performance in terms of good sensitivity, precise quantitative measurement, high spatial–temporal resolution, and fast response/recovery time. Their multiscale applications, such as regional environmental RH detection, internal humidity mapping, and sensitive human‐body humidity sensing are demonstrated. The proposed humidity visualization strategy may provide a new insight to develop humidity sensors for various applications.     

Microlasers from AIE‐Active BODIPY Derivative

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

Bright Aggregation‐Induced‐Emission Dots for Targeted Synergetic NIR‐II Fluorescence and NIR‐I Photoacoustic Imaging of Orthotopic Brain Tumors

Precise diagnostics are of significant importance to the optimal treatment outcomes of patients bearing brain tumors. NIR‐II fluorescence imaging holds great promise for brain‐tumor diagnostics with deep penetration and high sensitivity. This requires the development of organic NIR‐II fluorescent agents with high quantum yield (QY), which is difficult to achieve. Herein, the design and synthesis of a new NIR‐II fluorescent molecule with aggregation‐induced‐emission (AIE) characteristics is reported for orthotopic brain‐tumor imaging. Encapsulation of the molecule in a polymer matrix yields AIE dots showing a very high QY of 6.2% with a large absorptivity of 10.2 L g^?1 cm^?1 at 740 nm and an emission maximum near 1000 nm. Further decoration of the AIE dots with c‐RGD yields targeted AIE dots, which afford specific and selective tumor uptake, with a high signal/background ratio of 4.4 and resolution up to 38 µm. The large NIR absorptivity of the AIE dots facilitates NIR‐I photoacoustic imaging with intrinsically deeper penetration than NIR‐II fluorescence imaging and, more importantly, precise tumor‐depth detection through intact scalp and skull. This research demonstrates the promise of NIR‐II AIE molecules and their dots in dual NIR‐II fluorescence and NIR‐I photoacoustic imaging for precise brain cancer diagnostics.     

Corannulene‐Incorporated AIE Nanodots with Highly Suppressed Nonradiative Decay for Boosted Cancer Phototheranostics In Vivo

Fluorescent nanoparticles (NPs) based on luminogens with aggregation‐induced emission characteristic (AIEgens), namely AIE dots, have received wide attention because of their antiquenching attitude in emission and reactive oxygen species (ROS) generation when aggregated. However, few reports are available on how to control and optimize their fluorescence and ROS generation ability. Herein, it is reported that enhancing the intraparticle confined microenvironment is an effective approach to advanced AIE dots, permitting boosted cancer phototheranostics in vivo. Formulation of a “rotor‐rich” and inherently charged near‐infrared (NIR) AIEgen with 1,2‐distearoyl‐sn‐glycero‐3‐phosphoethanolamine‐N‐[methoxy(polyethylene glycol)‐2000] and corannulene‐decorated PEG affords DSPE‐AIE dots and Cor‐AIE dots, respectively. Compared to DSPE‐AIE dots, Cor‐AIE dots show 4.0‐fold amplified fluorescence quantum yield and 5.4‐fold enhanced ROS production, because corannulene provides intraparticle rigidity and strong interactions with the AIEgen to restrict the intramolecular rotation of AIEgen to strongly suppress the nonradiative decay and significantly facilitate the fluorescence pathway and intersystem crossing. Thus, it tremendously promotes phototheranostic efficacies in terms of NIR image‐guided cancer surgery and photodynamic therapy using a peritoneal carcinomatosis‐bearing mouse model. Collectively, it not only provides a novel strategy to advanced AIE dots for cancer phototheranostics, but also brings new insights into the design of superior fluorescent NPs for biomedical applications.     

Lipid‐PEG‐Folate Encapsulated Nanoparticles with Aggregation Induced Emission Characteristics: Cellular Uptake Mechanism and Two‐Photon Fluorescence Imaging

Folate functionalized nanoparticles (NPs) that contain fluorogens with aggregation‐induced emission (AIE) characteristics are fabricated to show bright far‐red/near‐infrared fluorescence, a large two‐photon absorption cross section and low cytotoxicity, which are internalized into MCF‐7 cancer cells mainly through caveolae‐mediated endocytosis. One‐photon excited in vivo fluorescence imaging illustrates that these AIE NPs can accumulate in a tumor and two‐photon excited ex vivo tumor tissue imaging reveals that they can be easily detected in the tumor mass at a depth of 400 μm. These studies indicate that AIE NPs are promising alternatives to conventional TPA probes for biological imaging.     

Aggregation‐Induced Nonlinear Optical Effects of AIEgen Nanocrystals for Ultradeep In Vivo Bioimaging

Nonlinear optical microscopy has become a powerful tool in bioimaging research due to its unique capabilities of deep optical sectioning, high‐spatial‐resolution imaging, and 3D reconstruction of biological specimens. Developing organic fluorescent probes with strong nonlinear optical effects, in particular third‐harmonic generation (THG), is promising for exploiting nonlinear microscopic imaging for biomedical applications. Herein, a simple method for preparing organic nanocrystals based on an aggregation‐induced emission (AIE) luminogen (DCCN) with bright near‐infrared emission is successfully demonstrated. Aggregation‐induced nonlinear optical effects, including two‐photon fluorescence (2PF), three‐photon fluorescence (3PF), and THG, of DCCN are observed in nanoparticles, especially for crystalline nanoparticles. The nanocrystals of DCCN are successfully applied for 2PF microscopy at 1040 nm NIR‐II excitation and THG microscopy at 1560 nm NIR‐II excitation, respectively, to reconstruct the 3D vasculature of the mouse cerebral vasculature. Impressively, the THG microscopy provides much higher spatial resolution and brightness than the 2PF microscopy and can visualize small vessels with diameters of ≈2.7 µm at the deepest depth of 800 µm in a mouse brain. Thus, this is expected to inspire new insights into the development of advanced AIE materials with multiple nonlinearity, in particular THG, for multimodal nonlinear optical microscopy.     

Precise Two‐Photon Photodynamic Therapy using an Efficient Photosensitizer with Aggregation‐Induced Emission Characteristics

Two‐photon photodynamic therapy (PDT) is able to offer precise 3D manipulation of treatment volumes, providing a target level that is unattainable with current therapeutic techniques. The advancement of this technique is greatly hampered by the availability of photosensitizers with large two‐photon absorption (TPA) cross section, high reactive‐oxygen‐species (ROS) generation efficiency, and bright two‐photon fluorescence. Here, an effective photosensitizer with aggregation‐induced emission (AIE) characteristics is synthesized, characterized, and encapsulated into an amphiphilic block copolymer to form organic dots for two‐photon PDT applications. The AIE dots possess large TPA cross section, high ROS generation efficiency, and excellent photostability and biocompatibility, which overcomes the limitations of many conventional two‐photon photosensitizers. Outstanding therapeutic performance of the AIE dots in two‐photon PDT is demonstrated using in vitro cancer cell ablation and in vivo brain‐blood‐vessel closure as examples. This shows therapy precision up to 5 µm under two‐photon excitation.     

Real‐Time and High‐Resolution Bioimaging with Bright Aggregation‐Induced Emission Dots in Short‐Wave Infrared Region

Fluorescence imaging in the spectral region beyond the conventional near‐infrared biological window (700–900 nm) can theoretically afford high resolution and deep tissue penetration. Although some efforts have been devoted to developing a short‐wave infrared (SWIR; 900–1700 nm) imaging modality in the past decade, long‐wavelength biomedical imaging is still suboptimal owing to the unsatisfactory materials properties of SWIR fluorophores. Taking advantage of organic dots based on an aggregation‐induced emission luminogen (AIEgen), herein microscopic vasculature imaging of brain and tumor is reported in living mice in the SWIR spectral region. The long‐wavelength emission of AIE dots with certain brightness facilitates resolving brain capillaries with high spatial resolution (≈3 µm) and deep penetration (800 µm). Owning to the deep penetration depth and real‐time imaging capability, in vivo SWIR microscopic angiography exhibits superior resolution in monitoring blood–brain barrier damage in mouse brain, and visualizing enhanced permeability and retention effect in tumor sites. Furthermore, the AIE dots show good biocompatibility, and no noticeable abnormalities, inflammations or lesions are observed in the main organs of the mice. This work will inspire new insights on development of advanced SWIR techniques for biomedical imaging.     

Endoplasmic Reticulum–Targeted Fluorescent Nanodot with Large Stokes Shift for Vesicular Transport Monitoring and Long‐Term Bioimaging

Herein, a highly stable aggregation‐induced emission (AIE) fluorescent nanodot assembled by an amphiphilic quinoxalinone derivative‐peptide conjugate, namely Quino‐1‐Fmoc‐RACR (also termed as Q1‐PEP), which exhibits large Stokes shift and an endoplasmic reticulum (ER)‐targeting capacity for bioimaging is reported. It is found that the resulting nanodot can effectively enter the ER with high fluorescent emission. As the ER is mainly involved in the transport of synthesized proteins in vesicles to the Golgi or lysosomes, the Q1‐PEP nanodot with ER‐targeting capacity can be used to monitor vesicular transport inside the cells. Compared to conventional fluorescent dyes with small Stokes shifts, the self‐assembled fluorescent nanodot shows superior resistance to photobleaching and aggregation‐induced fluorescence quenching, and elimination of the spectra overlap with autofluorescence of biosubstrate owning to their AIE‐active and red fluorescence emission characteristics. All these optical properties make the fluorescent nanodot suitable for noninvasive and long‐term imaging both in vitro and in vivo.     

Molecular Engineering of an Organic NIR‐II Fluorophore with Aggregation‐Induced Emission Characteristics for In Vivo Imaging

Design and synthesis of new fluorophores with emission in the second near‐infrared window (NIR‐II, 1000–1700 nm) have fueled the advancement of in vivo fluorescence imaging. Organic NIR‐II probes particularly attract tremendous attention due to excellent stability and biocompatibility, which facilitate clinical translation. However, reported organic NIR‐II fluorescent agents often suffer from low quantum yield and complicated design. In this study, the acceptor unit of a known NIR‐I aggregation‐induced emission (AIE) luminogen (AIEgen) is molecularly engineered by varying a single atom from sulfur to selenium, leading to redshifted absorption and emission spectra. After formulation of the newly prepared AIEgen, the resultant AIE nanoparticles (referred as L897 NPs) have an emission tail extending to 1200 nm with a high quantum yield of 5.8%. Based on the L897 NPs, noninvasive vessel imaging and lymphatic imaging are achieved with high signal‐to‐background ratio and deep penetration. Furthermore, the L897 NPs can be used as good contrast agents for tumor imaging and image‐guided surgery due to the high tumor/normal tissue ratio, which peaks at 9.0 ± 0.6. This work suggests a simple strategy for designing and manufacturing NIR‐II AIEgens and demonstrates the potential of NIR‐II AIEgens in vessel, lymphatic, and tumor imaging.     

Aggregation‐Induced Electrochemiluminescence by Metal‐Binding Protein Responsive Hydrogel Scaffolds

Functionalized hydrogels have aroused general interest due to their versatile applications in biomaterial fields. This work reports a hydrogel network composed of gold nanoclusters linked with bivalent cations such as Ca²⁺, Mg²⁺, and Zn²⁺. The hydrogel exhibits both aggregation‐induced emission (AIE) and aggregation‐induced electrochemiluminescence (AIECL) effects. Most noteworthy, the AIECL effect (≈50‐fold enhancement) is even more significant than the corresponding AIE effect (approximately fivefold enhancement). Calmodulin, a Ca²⁺ binding protein, may efficiently regulate the AIECL dynamics after specific binding of the Ca²⁺ linker, with the linear range from 0.3 to 50 µg mL^?1 and a limit of detection of 0.1 µg mL^?1. Considering the important roles of bivalent cations in the life system, these results may pave a new avenue for the design of a biomolecule‐responsive AIECL‐type hydrogel with multifunctional biomedical purposes.     

Eccentric Loading of Fluorogen with Aggregation‐Induced Emission in PLGA Matrix Increases Nanoparticle Fluorescence Quantum Yield for Targeted Cellular Imaging

A simple strategy is developed to prepare eccentrically or homogeneously loaded nanoparticles (NPs) using poly (DL‐lactide‐co‐glycolide) (PLGA) as the encapsulation matrix in the presence of different amounts of polyvinyl alcohol (PVA) as the emulsifier. Using 2,3‐bis(4‐(phenyl(4‐(1,2,2‐triphenylvinyl)‐phenyl)amino)‐phenyl)‐fumaronitrile (TPETPAFN), a fluorogen with aggregation‐induced emission (AIE) characteristics, as an example, the eccentrically loaded PLGA NPs show increased fluorescence quantum yields (QYs) as compared to the homogeneously loaded ones. Field emission transmission electron microscopy and fluorescence lifetime measurements reveal that the higher QY of the eccentrically loaded NPs is due to the more compact aggregation of AIE fluorogens that restricts intramolecular rotations of phenyl rings, which is able to more effectively block the non‐radiative decay pathways. The eccentrically loaded NPs show far red/near infrared emission with a high fluorescence QY of 34% in aqueous media. In addition, by using poly([lactide‐co‐glycolide]‐b‐folate [ethylene glycol]) (PLGA‐PEG‐folate) as the co‐encapsulation matrix, the obtained NPs are born with surface folic acid groups, which are successfully applied for targeted cellular imaging with good photostability and low cytotoxicity. Moreover, the developed strategy is also demonstrated for inorganic‐component eccentrically or homogeneously loaded PLGA NPs, which facilitates the synthesis of polymer NPs with controlled internal architectures.     

Full‐Color Tunable Circularly Polarized Luminescent Nanoassemblies of Achiral AIEgens in Confined Chiral Nanotubes

Circularly polarized luminescent (CPL) materials are currently attracting great interest. While a chiral building is usually necessary in order to obtain CPL materials, here, this study proposes a general approach for fabricating 1D circularly polarized luminescent nanoassemblies from achiral aromatic molecules or aggregation‐induced emissive compounds (AIEgens). It is found that a C₃ symmetric chiral gelator can individually form hexagonal nanotube structures and encapsulate the guest molecules. When achiral AIEgens are encapsulated into the confined nanotubes via organogelation, the AIEgens will emit circularly polarized luminescence. Further, the direction of the CPL could be controlled by the supramolecular chirality of the nanotube. Remarkably, the approach is universal and various kinds of the AIEgens can be doped to show such property, providing a full‐color‐tunable circularly polarized luminescence.     

Modular Molecular Self‐Assembly for Diversified Chiroptical Systems

Bottom‐up multicomponent molecular self‐assembly is an efficient approach to fabricate and manipulate chiral nanostructures and their chiroptical activities such as the Cotton effect and circular polarized luminescence (CPL). However, the integrated coassembly suffers from spontaneous and inherent systematic pathway complexity with low yield and poor fidelity. Consequently, a rational design of chiral self‐assembled systems with more than two components remains a significant challenge. Herein, a modularized, ternary molecular self‐assembly strategy that generates chiroptically active materials at diverse hierarchical levels is reported. N‐terminated aromatic amino acids appended with binding sites for charge transfer and multiple hydrogen bonds undergo the evolution of supramolecular chirality with unique handedness and luminescent color, generating abundant CPL emission with high luminescence dissymmetry factor values in precisely controlled modalities. Ternary coassembly facilitates high‐water‐content hydrogel formation constituted by super‐helical nanostructures, demonstrating a helix to toroid topological transition. This discovery would shed light on developing complicated multicomponent systems in mimicking biological coassembly events.     

Mitochondria‐Targeted Polydopamine Nanocomposite with AIE Photosensitizer for Image‐Guided Photodynamic and Photothermal Tumor Ablation

Photodynamic therapy (PDT) and photothermal therapy (PTT) are two kinds of treatment for tumors. Herein, a new aggregation‐induced emission (AIE)gen (MeO‐TPE‐indo, MTi) is synthesized with a D–π–A conjugated structure. MTi, which has an electron donor and an acceptor on a tetraphenylethene (TPE) conjugated skeleton, can induce the effective generation of reactive oxygen species (ROS) for PDT. With the guide of the indolium group, MTi can target and image mitochondrion selectively. In order to get good dispersion in water and long‐time retention in tumors, MTi is modified on the surface of polydopamine nanoparticles (PDA NPs) to form the nanocomposite (PDA‐MeO‐TPE‐indo, PMTi ) by π–π and hydrogen interactions. PMTi is a nanoscale composite for imaging‐guided PDT and PTT in tumor treatment, which is constructed with AIEgens and PDA for the first time. The organic functional molecules are combined with nanomaterials for building a multifunctional diagnosis and treatment platform by utilizing the advantages of both sides.     

Stereotactic Photodynamic Therapy Using a Two‐Photon AIE Photosensitizer

Two‐photon photodynamic therapy (TP‐PDT) is emerging as a powerful strategy for stereotactic targeting of diseased areas, but ideal photosensitizers (PSs) are currently lacking. This work reports a smart PS with aggregation‐induced emission (AIE) feature, namely DPASP, for TP‐PDT with excellent performances. DPASP exhibits high affinity to mitochondria, superior photostability, large two‐photon absorption cross section as well as efficient reactive oxygen species generation, enabling it to achieve photosensitization both in vitro and in vivo under two‐photon excitation. Moreover, its capability of stereotactic ablation of targeted cells with high‐precision is also successfully demonstrated. All these merits make DPASP a promising TP‐PDT candidate for accurate ablation of abnormal tissues with minimal damages to surrounding areas in the treatment of various diseases.     

Spontaneous Assembly of Extremely Long,Horizontally‐Aligned,Conductive Gold Micro‐Wires in a Langmuir Monolayer Template

“Bottom‐up” technologies are based upon the premise that organized systems – from the nano‐scale up to the macro‐scale – can be assembled spontaneously from basic building blocks in solution. We demonstrate a simple strategy for the generation of extremely long (up to several centi­meters), horizontally‐aligned gold micro‐wires, produced through a surfactant monolayer template deposited from gold thiocyanate [Au(SCN)₄⁻] aqueous solution. Specifically, we show that the surfactant, octyl‐maleimide (OM), spontaneously forms oriented micro‐wires at the air/water interface, which constitute a template for deposition of metallic gold through binding and crystallization of the soluble gold complex. The Au micro‐wires can be subsequently transferred onto solid substrates, and following plasma treatment and gold enhancement exhibit excellent conductivity even at electrode spacings of several centimeters. Importantly, the micro‐wire alignment determines the direction of electrical current, demonstrating that long‐range ordering of the micro‐wires can be accomplished, significantly affecting the physical properties of the system. The new approach is simple, robust, and can be readily exploited for bottom‐up fabrication of micro‐wire assemblies and transparent conductive electrodes.