ACQ‐to‐AIE Transformation: Tuning Molecular Packing by Regioisomerization for Two‐Photon NIR Bioimaging

The Midas Touch by Iridium: A Second Near-Infrared Aggregation-Induced Emission-Active Metallo-Agent for Exceptional Phototheranostics of Breast Cancer

Developing small organic molecular phototheranostic agents with second near-infrared (NIR-II) aggregation-induced emission (AIE) is paramount for the phototriggered diagnostic imaging and synchronous in situ therapy of cancer via an excellent balance of the excited states energy dissipations. In this study, a multifunctional iridium(III) complex is exploited by the coordination of an AIE-active N^N ancillary ligand with a trivalent iridium ion. The resultant complex DPTPzIr significantly outperforms its parent ligand in terms of absorption/emission wavelengths, reactive oxygen species (ROS) production, and photothermal conversion, which simultaneously endow DPTPzIr nanoparticles with matched absorption peak to commercial 808 nm laser, the longest NIR-II emission peak (above 1100 nm) among those previously reported AIE iridium(III) complexes, potentiated type-I ROS generation, and as high as 60.5% of photothermal conversion efficiency. Consequently, DPTPzIr nanoparticles perform well in multimodal image-guided photodynamic therapy-photothermal therapy for breast cancer in tumor-bearing mice, enabling precise tumor diagnosis and complete ablation with high biocompatibility. Our present work provides a simple, feasible, and effective paradigm for the development of advanced phototheranostic agents.

Near-Infrared Bioimaging Using Two-photon Fluorescent Probes

Near-infrared (NIR) bioimaging has emerged as a transformative technology in biomedical research. Among many fluorescent probes that are suitable for NIR imaging studies, two-photon absorption (TPA) ones represent a particularly promising category, because TPA fluorescent probes can overcome the inherent limitations of one-photon absorption (OPA) counterparts. By leveraging the unique properties of two-photon absorption, TPA fluorescent probes achieve superior tissue penetration, significantly reduced photodamage, and enhanced spatial resolution. This perspective article delves into the fundamental principles, design strategies, and representative TPA probes for various imaging applications. In particular, a number of molecular fluorescent probes, ranging from organic, inorganic, and COF/MOF-based systems are highlighted to showcase the vast scope of possible TPA probe design and application scenarios. In addition, the employment of stimulated TPA probes that are responsive to different external factors, including pH, redox species, enzymes, and hypoxia, is also discussed. In the end, the future perspectives for the continuous advancement of TPA fluorescent probes in the NIR bioimaging field are presented. For instance, it is essential to transition from cellular to in vivo imaging studies to obtain more physiologically relevant insights. Additionally, the development of "dual-function" TPA probes for both disease diagnosis and therapeutic treatment is particularly promising.

Development of a β-lactamase-based aggregation-induced emission lateral flow strip for the detection of clavulanic acid in Milk

Lack of biorecognition elements significantly hinders the development of rapid detection methods for clavulanic acid (CA). To address this, we expressed Class A β-lactamases PC1 in vitro and demonstrated its high affinity for CA. Then we investigated the recognition mechanisms of PC1 for CA and identified key contact amino acids: Ser70, Lys73, Ser130, Glu166, and Lys234. Furthermore, PC1 was utilized as a novel biorecognition element to establish a "pseudo-immuno" lateral flow strip (LFS) for CA detection. Aggregation-induced emission fluorescence microspheres (AIE@FM) and biotin-streptavidin (Bio-SA) were integrated to improve the detection performance of PC1-based LFS. Results showed that the sensitivity (cut-off value) of PC1-based AIE(Bio-SA)-LFS was enhanced 2-fold and 4-fold compared to basic AIE@FM-LFS and traditional Au-based LFS, respectively. Eventually, the proposed PC1-based AIE(Bio-SA)-LFS was successfully verified in milk samples with a cut-off value of 20 ng mL-1. This study provides a powerful tool for on-site CA monitoring for the first time.

Aggregation-induced emission: Application in diagnosis and therapy of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a serious health issue due to its low early diagnosis rate, resistance to chemotherapy, and poor five-year survival rate. Therefore, it is crucial to explore novel diagnostic and therapeutic approaches tailored to the characteristics of HCC. Aggregation-induced emission (AIE) is a phenomenon where the luminescence of certain molecules, typically non-luminescent or weakly luminescent in solution, is significantly enhanced upon aggregation. AIE has been extensively applied in bioimaging, biosensors, and therapy. Fluorophore materials based on AIE (AIEgens) have a wide range of application scenarios and potential for clinical translation. This review focuses on recent advances in AIE-based strategies for diagnosing and treating HCC. First, the specific functional mechanism of AIE is described. Next, we summarize recent progress in the application of AIE for multimodal imaging, biosensor detection, and phototherapy. Finally, prospects and challenges for the AIE-based application in the diagnosis and therapy of HCC are discussed.

TADF-Guiding Modification of Endoplasmic Reticulum-Targeted Photosensitizers for Efficient Photodynamic Immunotherapy

Pharmacological activation of the immunogenic cell death (ICD) pathway by endoplasmic reticulum (ER) targeted photosensitizer (PS) has become a promising strategy for tumor immunotherapy. Despite a clear demand for ER-targeted PS, the sluggish intersystem crossing (ISC) process, unstable excited state, insufficient ROS production, and immunosuppressive tumor microenvironment (ITME) combined to cause the high-efficiency agents are still limited. Herein, three groups commonly used in thermally activated delayed fluorescence (TADF) molecular design are used to modify the excited state characteristics of xanthene-based cyanine PS (obtained the XCy-based PS). The electronic and geometric modulation effectively optimize the excited state characteristics, facilitating the ISC process and prolonging the excited state life for boosting ROS generation. Among them, car-XCy showed 100 times longer excited state life and 225% higher ROS yield than that of original XCy. The satisfactory ROS production and ER-targeted ability of car-XCy arouse intense ER stress to activate the ICD. Adequate antigen presentation promotes the dendritic cell maturation and infiltration of cytotoxic T lymphocytes (CTLs), ultimately reversing the ITME to realize efficient immunotherapy. As a result, significant inhibition is observed in both primary and distant tumors, underscoring the efficacy of this TADF-guiding excited state characteristics modulation strategy for developing photodynamic immunotherapy drugs.

Intermolecular Assembly of Dual Hydrogen Bonding Regio-Isomers Generates High-Performance AIE Probes

Regio-isomers are utilized to design innovative AIE luminogens (AIEgens) by regulating molecular aggregation behavior. However, relevant examples are limited, and the underlying mechanism is not fully understood. Herein, a regio-isomer strategy is used to develop AIEgens by precisely regulating the intermolecular interactions in the solid state. Among the regio-isomers it is investigated, ortho- isomer (DCM-O3-O7) exhibits enhanced AIE-activity than the para- isomer (DCM-P6), and the size of the ortho- substituents is crucial for the AIE performance. The underlying mechanism of the strategy is revealed using DFT calculations and single-crystal analysis. Dual hydrogen bonds (C─H∙∙∙π and C─H∙∙∙N) are generated between the molecules, which contributes to form dimers, tetramers, and 1D supramolecular structures in the crystal. By restricting intramolecular motion and attenuating π-π interactions, solid-state fluorescence is significantly enhanced. This strategy's effectiveness is validated using other donor-acceptor fluorophores, with DCM-O6 and its analogues serving as efficient probes for bioimaging applications. Notably, DCM-OM, which bears a morpholinyl instead of piperidinyl group, displayed strong lysosome-targeting ability and photostability; DCM-OP, incorporated by the hydrophilic quaternary ammonium group, exhibited wash-free imaging and cell membrane-targeting capabilities; and DCM-O6 nanoparticles enabled high-fidelity in vivo tumor imaging. Therefore, this strategy affords a general method for designing bright AIEgens.

General Post-Regulation Strategy of AIEgens' Photophysical Properties for Intravital Two-Photon Fluorescence Imaging

Fluorogens with aggregation-induced emission (AIEgens) are promising agents for two-photon fluorescence (TPF) imaging. However, AIEgens' photophysical properties are fixed and unoptimizable once synthesized. Therefore, it is urgent and meaningful to explore an efficient post-regulation strategy to optimize AIEgens' photophysical properties. Herein, a general and efficient post-regulation strategy is reported. By simply tuning the ratio of inert AIEgens within binary nanoparticles (BNPs), the fluorescence quantum yield and two-photon absorption cross-section of functional AIEgens are enhanced by 8.7 and 5.4 times respectively, which are not achievable by conventional strategies, and the notorious phototoxicity is almost eliminated. The experimental results, theoretical simulation, and mechanism analysis demonstrated its feasibility and generality. The BNPs enabled deep cerebrovascular network imaging with ≈1.10 mm depth and metastatic cancer cell detection with single-cell resolution. Furthermore, the TPF imaging quality is improved by the self-supervised denoising algorithm. The proposed binary molecular post-regulation strategy opened a new avenue to efficiently boost the AIEgens' photophysical properties and consequently TPF imaging quality.

Isomer engineering for deep understanding of aggregation-induced photothermal enhancement in conjugated systems

Organic photothermal materials based on conjugated structures have significant potential applications in areas such as biomedical diagnosis, therapy, and energy conversion. Improving their photothermal conversion efficiency through molecular design is critical to promote their practical applications. Especially in similar structures, understanding how the position of heteroatoms affects the conversion efficiency is highly desirable. Herein, we prepared two isomeric small D-A molecules with different sulfur atom positions (TBP-MPA and i-TBP-MPA), which display strong and broad absorption in the UV-visible region due to their strong intramolecular charge transfer characteristics. Compared to i-TBP-MPA, TBP-MPA demonstrates aggregation-induced photothermal enhancement (AIPE). Under simulated sunlight (1 kW m-2) irradiation, the stable temperature of TBP-MPA powder reached 60 °C, significantly higher than the 50 °C achieved by i-TBP-MPA. Experimental and theoretical results indicate that the S⋯N non-covalent interactions in TBP-MPA impart a more rigid conjugated framework to the molecule, inducing ordered molecular stacking during aggregation. This ordered stacking provides additional non-radiative transition channels between TBP-MPA molecules, enhancing their photothermal performance in the aggregated state. Under 1 sun irradiation, TBP-MPA achieved a water evaporation rate of 1.0 kg m-2 h-1, surpassing i-TBP-MPA's rate of 0.92 kg m-2 h-1.

A Long-Retention Cell Membrane-Targeting AIEgen for Boosting Tumor Theranostics

Designing and developing photosensitizers with cell membrane specificity is crucial for achieving effective multimodal therapy of tumors compared to other organelles. Here, we designed and screened a photosensitizer CM34 through donor/receptor regulation strategies, and it is able to achieve long-retention cell membrane targeting. It is not only an extremely excellent cell membrane targeted tumor theranostic agent, but also found to be a promising potential immune activator. Specifically, CM34 with a larger intramolecular twist angle is more likely to form larger aggregates in aqueous solutions, and the introduction of cyanide group also enhances its interaction with cell membranes, which were key factors hindering molecular penetration of the cell membrane and prolonging its residence time on the cell membrane, providing conditions for further membrane targeted photodynamic therapy. Furthermore, the efflux of contents caused by cell necrosis directly activates the immune response. In summary, this study realizes to clarify and refine all potential mechanisms of action through density functional theory calculations, photophysical property measurements, and cellular level mechanism exploration, providing a new direction for the clinical development of cell membrane targeted anti-tumor immune activators.

Thiophene π-bridge-based second near-infrared luminogens with aggregation-induced emission for biomedical applications

In the past 5 years, aggregation-induced emission luminogens (AIEgens) with emission in the second near-infrared (NIR-II) optical window have aroused great interest in bioimaging and disease phototheranostics, benefiting from the merits of deep penetration depth, reduced light scatting, high spatial resolution, and minimal photodamage. To construct NIR-II AIEgens, thiophene derivatives are frequently adopted as π-bridge by virtue of their electron-rich feature and good modifiability. Herein, we summarize the recent progress of NIR-II AIEgens by employing thiophene derivatives as π-bridge mainly compassing unsubstituted thiophene, alkyl thiophene, 3,4-ethylenedioxythiophene, and benzo[c]thiophene, with a discussion on their structure-property relationships and biomedical applications. Finally, a brief conclusion and perspective on this fascinating area are offered.

Reviewing the evolutive ACQ-to-AIE transformation of photosensitizers for phototheranostics

Photodynamic therapy (PDT) represents an emerging noninvasive treatment technique for cancers and various nonmalignant diseases, including infections. During the process of PDT, the physical and chemical properties of photosensitizers (PSs) critically determine the effectiveness of PDT. Traditional PSs have made great progress in clinical applications. One of the challenges is that traditional PSs suffer from aggregation-caused quenching (ACQ) due to their discotic structures. Recently, aggregation-induced emission PSs (AIE-PSs) with a twisted propeller-shaped conformation have been widely concerned because of high reactive oxygen species (ROS) generation efficiency, strong fluorescence efficiency, and resistance to photobleaching. However, AIE-PSs also have some disadvantages, such as short absorption wavelengths and insufficient molar absorption coefficient. When the advantages and disadvantages of AIE-PSs and ACQ-PSs are complementary, combining ACQ-PSs and AIE-PSs is a "win-to-win" strategy. As far as we know, the conversion of traditional representative ACQ-PSs to AIE-PSs for phototheranostics has not been reviewed. In the review, we summarize the recent progress on the ACQ-to-AIE transformation of PSs and the strategies to achieve desirable theranostic applications. The review would be helpful to design more efficient ACQ-AIE-PSs in the future and to accelerate the development and clinical application of PDT.

Overcome the "Buckets Effect": Integration of AIEgens into Proteins for Fluorescence-Enhanced Two-Photon Imaging

Luminogens with aggregation-induced emission characteristics (AIEgens) are considered good options for two-photon (2P) probes, owing to their flexibility of design, heavy-metal-free composition, and resistance to photobleaching. However, the design principles for large 2P absorption cross-section (δ) generally require high coplanarity, strong donor-acceptor (D-A) interactions, and long conjugation, which can severely weaken the brightness of AIEgens at the aggregated state and undermine their potential in 2P fluorescence imaging (2PFI). Exploration of a feasible approach to overcome the "Buckets Effect" of AIEgen-based 2P probes is thus a fascinating yet challenging task. Herein, an AIEgen, namely (Z)-2-(4-aminophenyl)-3-(5-(4-(bis(4-methoxyphenyl)amino)phenyl)thiophen-2-yl)acrylonitrile (MTAA) is designed to have a big δ according to the calculation result and a low fluorescence quantum yield (QY) of 2.2% in dimethyl sulfoxide (DMSO). Impressively, upon integrating into bovine serum albumin (BSA), the protein-sized MTAA@BSA dots exhibit a 25-fold higher fluorescence QY compared to MTAA molecules, contributing to an imaging depth of 818 µm in the brain vasculature. The retention and clearance of MTAA@BSA dots in the liver and kidney are also studied using 2PFI. Overall, this work provides a facile approach to overcome the "Buckets Effect" of AIEgen to generate highly efficient, reliable, and biocompatible 2P probes.

Exploration of Water-Soluble Natural AIEgens Boosting Label-Free Turn-on Fluorescent Sensing in a DNA Hydrogel

Various aggregation-induced emission luminogens (AIEgens) have been developed and applied in different areas in recent years. However, AIEgens generally can aggregate and emit strong fluorescence in aqueous solution even containing DNA and other biomacromolecules because of poor water solubility, restricting their application in biosensing and bioimaging in aqueous solution. Moreover, the great majority of AIEgens commonly suffer from complex organic synthesis, environmental damage, and biological toxicity. In this work, jatrorrhizine (Jat), an isoquinoline alkaloid from Chinese herbs, was found to be a natural water-soluble AIEgen that has not been previously reported. Jat's photometric characteristics and single-crystal structure demonstrated that the restriction of intramolecular motion and twisted intramolecular charge transfer were responsible for its AIE phenomenon. Due to the good water solubility and AIE character of Jat, it did not emit fluorescence in the aqueous solution containing DNA and polymers until the formation of the DNA hydrogel. Therefore, a DNA hydrogel fluorescence biosensor was designed by using the target (miRNA) as a catalyst to trigger the entropy-driven circuit of DNA, realizing the ultrasensitive and label-free detection of miRNA with an ultralow limit of detection (0.049 fM, S/N = 3). This biosensing strategy also has excellent stability and acceptable reliability for real sample assay. The results not only indicated the excellent sensing performance of Jat as AIE probes in aqueous solution but also demonstrated the promising application potential of water-soluble natural AIEgens.

Mesoporous Silica-Encapsulated Gold Nanorods for Drug Delivery/Release and Two-Photon Excitation Fluorescence Imaging to Guide Synergistic Phototherapy and Chemotherapy

Photothermal therapy is a promising light-based medical treatment that relies on light absorption agents converting light irradiation into localized heat to destroy cancer cells or other diseased tissues. It is critical to enhance the therapeutic effects of cancer cell ablation for their practical applications. This study reports a high-performance combinational therapy for ablating cancer cells, including both photothermal therapy and chemotherapy to improve therapeutic efficiency. The prepared AuNR@mSiO2 loading molecular Doxorubicin (Dox) assemblies were highlighted by merits of facile acquisition, great stability, easy endocytosis, and rapid drug release in addition to improved anticancer capability upon irradiation with a femtosecond pulsed near-infrared (NIR) laser, where AuNR@mSiO2 nanoparticles afforded a high photothermal conversion efficiency of 31.7%. Two-photon excitation fluorescence imaging was introduced into confocal laser scanning microscope multichannel imaging to track the drug location and cell position in real time for monitoring the process of drug delivery in killing human cervical cancer HeLa cells and then to realize imaging-guiding cancer treatment. These nanoparticles exhibit widespread potential in photoresponsive utilizations including photothermal therapy, chemotherapy, one- and two-photon excited fluorescence imaging, and 3D fluorescence imaging and cancer treatment.

Two-photon nanoprobes based on bioorganic nanoarchitectonics with a photo-oxidation enhanced emission mechanism

Two-photon absorption (TPA) fluorescence imaging holds great promise in diagnostics and biomedicine owing to its unparalleled spatiotemporal resolution. However, the adaptability and applicability of currently available TPA probes, which act as a critical element for determining the imaging contrast effect, is severely challenged by limited photo-luminescence in vivo. This is particularly a result of uncontrollable aggregation that causes fluorescence quenching, and inevitable photo-oxidation in harsh physiological milieu, which normally leads to bleaching of the dye. Herein, we describe the remarkably enhanced TPA fluorescence imaging capacity of self-assembling near-infrared (NIR) cyanine dye-based nanoprobes (NPs), which can be explained by a photo-oxidation enhanced emission mechanism. Singlet oxygen generated during photo-oxidation enables chromophore dimerization to form TPA intermediates responsible for enhanced TPA fluorescence emission. The resulting NPs possess uniform size distribution, excellent stability, more favorable TPA cross-section and anti-bleaching ability than a popular TPA probe rhodamine B (RhB). These properties of cyanine dye-based TPA NPs promote their applications in visualizing blood circulation and tumoral accumulation in real-time, even to cellular imaging in vivo. The photo-oxidation enhanced emission mechanism observed in these near-infrared cyanine dye-based nanoaggregates opens an avenue for design and development of more advanced TPA fluorescence probes.

Synthesis of an aggregation-induced emission-based fluorescent probe based on rupestonic acid

Chinese herbal medicine and Chinese patent medicine have been widely applied for cancer care in China. Rupestonic acid, an active ingredient of Artemisia rupestris L., has recently been confirmed to have certain anti-tumor effects in vitro. In this study, we employed the application of a commonly devoted triphenylamine as a fluorophore and the addition of 2,4-thiazolidinedione as a bridge to integrate rupestonic acid into the AIE system to create an fluorescent probe with anti-tumor properties. The spectral, cytotoxic, and cellular imaging properties of the probe were measured. Its promising responses make possible the application of the probe in antitumor theragnostic systems.

Conformationally confined three-armed supramolecular folding for boosting near-infrared biological imaging

Herein, a triphenylamine derivative (TP-3PY) possessing 4-(4-bromophenyl)pyridine (PY) as an electron-accepting group and tris[p-(4-pyridylvinyl)phenyl]amine (TPA) with large two-photon absorption cross-sections as an electron-donating group was obtained, and showed intense absorption in the visible light region (λmax = 509 nm) and weak near-infrared (NIR) fluorescence emission at 750 nm. After complexation with cucurbit[8]uril (CB[8]), TP-3PY showed bright NIR fluorescence emission at 727 nm and phosphorescence emission at 800 nm. When the supramolecular assembly (TP-3PY⊂CB[8]) further interacted with dodecyl-modified sulfonatocalix[4]arene (SC4AD), the fluorescence and phosphorescence emissions were further enhanced at 710 and 734 nm, respectively. However, only the fluorescence emission of TP-3PY was enhanced in the presence of cucurbit[7]uril (CB[7]) and SC4AD. More interestingly, the photoluminescence of TP-3PY⊂CB[8]@SC4AD and TP-3PY⊂CB[7]@SC4AD assemblies could be excited by both visible (510 nm) and NIR light (930 nm). Finally, these ternary supramolecular assemblies with bright NIR light emission were applied to lysosome imaging of tumor cells and real-time biological imaging of mice.

NIR-II Fluorescence Imaging for the Detection and Resection of Cancerous Foci and Lymph Nodes in Early-Stage Orthotopic and Advanced-Stage Metastatic Ovarian Cancer Models

The high mortality rate of ovarian cancer can be primarily attributed to late diagnosis and early lymph node (LN) metastasis. The anatomically deep-located ovaries own intricate anatomical structures and lymphatic drainages that compromise the resolution and sensitivity of near-infrared first-window (NIR-I) fluorescence imaging. Reported NIR-II imaging studies of ovarian cancer focused on late-stage metastasis detection via the intraperitoneal xenograft model. However, given the significant improvement in patient survival associated with early-stage cancer detection, locating tumors that are restricted within the ovary is equally crucial. We obtained the polymer nanoparticles with bright near-infrared-II fluorescence (NIR-II NPs) by nanoprecipitation of DSPE-PEG, one of the ingredients of FDA-approved nanoparticle products, and benzobisthiadiazole, an organic NIR-II dye. The one-step synthesis and safe component lay the groundwork for its clinical translation. Benefiting from the NIR-II emission (∼1060 nm), NIR-II NPs enabled a high signal-to-noise (S/N) ratio (13.4) visualization of early-stage orthotopic ovarian tumors with NIR-II fluorescence imaging for the first time. Imaging with orthotopic xenograft allows a more accurate mimic of human ovarian cancer origin, thereby addressing the dilemma of translating existing nanoprobe preclinical research by providing the nano-bio interactions with early local tumor environments. After PEGylation, the desirable-sized probe (∼80 nm) exhibited high lymphophilicity and relatively extended circulation. NIR-II NPs maintained their accurate detection of orthotopic tumors, tumor-regional LNs, and minuscule (<1 mm) disseminated peritoneal metastases simultaneously (with S/N ratios all above 5) in mice with advanced-stage cancer in real time ∼36 h after systematic delivery. With NIR-II fluorescence guidance, we achieved accurate surgical staging in tumor-bearing mice and complete tumor removal comparable to clinical practice, which provides preclinical data for translating NIR-II fluorescence image-guided surgery.

Interactions of Amino Group Functionalized Tetraphenylvinyl and DNA: A Label-Free "On-Off-On" Fluorescent Aptamer Sensor toward Ampicillin

As a type of aggregation-induced emission (AIE) fluorescent probe, tetraphenylvinyl (TPE) or its derivatives are widely used in chemical imaging, biosensing and medical diagnosis. However, most studies have focused on molecular modification and functionalization of AIE to enhance the fluorescence emission intensity. There are few studies on the interaction between aggregation-induced emission luminogens (AIEgens) and nucleic acids, which was investigated in this paper. Experimental results showed the formation of a complex of AIE/DNA, leading to the quenching of the fluorescence of AIE molecules. Fluorescent test experiments with different temperatures proved that the quenching type was static quenching. The quenching constants, binding constants and thermodynamic parameters demonstrated that electrostatic and hydrophobic interactions promoted the binding process. Then, a label-free "on-off-on" fluorescent aptamer sensor for the detection of ampicillin (AMP) was constructed based on the interaction between the AIE probe and the aptamer of AMP. Linear range of the sensor is 0.2-10 nM with a limit of detection 0.06 nM. This fluorescent sensor was applied to detect AMP in real samples.

Molecular and Aggregate Synergistic Engineering of Aggregation-Induced Emission Luminogens to Manipulate Optical/Electronic Properties for Efficient and Diversified Functions

The optical/electronic properties of organic luminescent materials can be regulated by molecular structure modification, which not only requires sophisticated and time-consuming synthesis but also is unable to accurately afford the optical properties of materials in the aggregate state. Herein, a facile strategy of molecular and aggregate synergistic engineering is proposed to manipulate the optical/electronic properties of a luminogen, ACIK, in the solid state for efficient and diversified functions. ACIK is facilely synthesized and exhibits three polymorphic states (ACIK-Y, ACIK-R, and ACIK-N) with a large emission difference of 102 nm from yellow to near-infrared (NIR). Their structure-property relationships were investigated by crystallographic analyses and computational studies. ACIK-Y, with the most twisted structure, exhibits an intriguing color-tuned fluorescence between yellow and NIR in the solid state in response to multiple stimuli. Shuttle-like ACIK-R microcrystals exhibit an optical waveguide property with a low optical loss coefficient of 19 dB mm^-1. ACIK dots display bright NIR-I emission, large Stokes shift, and strong NIR-II two-photon absorption. ACIK dots show specific lipid droplets-targeting capability and can be successfully applied for two-photon fluorescence imaging of mouse brain vasculature with deep penetration and high spatial resolution. This study will inspire more insights in developing advanced optical/electronic materials based on a single chromophore for practical applications.

Systematic Study of Solid-State Fluorescence and Molecular Packing of Methoxy-trans-Stilbene Derivatives, Exploration of Weak Intermolecular Interactions Based on Hirshfeld Surface Analysis

In recent years, fluorescent compounds that emit efficiently in the solid state have become particularly interesting, especially those that are easily prepared and inexpensive. Hence, exploring the photophysical properties of stilbene derivatives, supported by a detailed analysis of molecular packing obtained from single-crystal X-ray diffraction data, is a relevant area of research. A complete understanding of the interactions to determine the molecular packing in the crystal lattice and their effect on the material's physicochemical properties is essential to tune various properties effectively. In the present study, we examined a series of methoxy-trans-stilbene analogs with substitution pattern-dependent fluorescence lifetimes between 0.82 and 3.46 ns and a moderate-to-high fluorescence quantum yield of 0.07-0.69. The relationships between the solid-state fluorescence properties and the structure of studied compounds based on X-ray analysis were investigated. As a result, the QSPR model was developed using PLSR (Partial Least Squares Regression). Decomposition of the Hirshfeld surfaces (calculated based on the arrangement of molecules in the crystal lattice) revealed the various types of weak intermolecular interactions that occurred in the crystal lattice. The obtained data, in combination with global reactivity descriptors calculated using HOMO and LUMO energy values, were used as explanatory variables. The developed model was characterized by good validation metrics (RMSE_CAL = 0.017, RMSE_CV = 0.029, R²_CAL = 0.989, and R²_CV = 0.968) and indicated that the solid-state fluorescence quantum yield of methoxy-trans-stilbene derivatives was mainly dependent on weak intermolecular C…C contacts corresponding to π-π stacking and C…O/O…C interactions. To a lesser extent and inversely proportional, the fluorescence quantum yield was affected by the interactions of the type O…H/H…O and H…H and the electrophilicity of the molecule.

Structural Engineering of Red Luminogens to Realize High Emission Efficiency through ACQ-to-AIE Transformation

Deep red/near-infrared (NIR, >650 nm) emissive organic luminophores with aggregation-induced emission (AIE) behaviours have emerged as promising candidates for applications in optoelectronic devices and biological fields. However, the molecular design philosophy for AIE luminogens (AIEgens) with narrow band gaps are rarely explored. Herein, we rationally designed two red organic luminophores, FITPA and FIMPA, by considering the enlargement of transition dipole moment in the charge-transfer state and the transformation from aggregation-caused quenching (ACQ) to AIE. The transition dipole moments were effectively enhanced with a "V-shaped" molecular configuration. Meanwhile, the ACQ-to-AIE transformation from FITPA to FIMPA was induced by a methoxy-substitution strategy. The experimental and theoretical results demonstrated that the ACQ-to-AIE transformation originated from a crystallization-induced emission (CIE) effect because of additional weak interactions in the aggregate state introduced by methoxy groups. Owing to the enhanced transition dipole moment and AIE behaviour, FIMPA presented intense luminescence covering the red-to-NIR region, with a photoluminescence quantum yield (PLQY) of up to 38 % in solid state. The promising cell-imaging performance further verified the great potential of FIMPA in biological applications. These results provide a guideline for the development of red and NIR AIEgens through comprehensive consideration of both the effect of molecular structure and molecular interactions in aggregate states.

Ultrasensitive lateral flow immunoassay for staphylococcal enterotoxin B using nanosized fluorescent metal-organic frameworks

Owing to their outstanding optical properties and superior physical/chemical stability, dye-doped fluorescent nanoparticles (NPs) are growing exponentially as signal labels of immunochromatographic lateral flow immunoassay (LFA) for the detection of various analytes. However, the key challenge in the design of these fluorescent NPs is to confine the fluorophores inside NPs at extreme concentrations, at which dyes tend to self-quench resulting from the formation of non-fluorescent aggregates. Looking for other advantageous nanomaterials, we propose for the first time the use of a nanosized fluorescent metal-organic framework (nanoMOF) in LFA for the detection of staphylococcal enterotoxin B (SEB) as a model analyte. Featured by the chromophore assembly, the nanoMOF exhibited a high dye loading (∼60%) and strong fluorescence intensity, which was due to the reduced self-quenching of dyes in a variety of MOF matrices. The strong green fluorescence intensity of the nanoMOF gives a high contrast against the background of the strips and the sensitivity reflected by photoluminescence was improved by the enhanced antenna effect. Furthermore, due to the high surface area for antibody stemming, the limit of detection (LOD) of the MOF based LFA for SEB detection was as low as 0.025 ng mL^-1. The compatibility of the MOF based LFA with dairy samples and its stability under long-term storage conditions were also demonstrated. The integration of a nanoMOF into LFA to detect toxins could inspire the utilization of such nanomaterial-based labels in similar immunochromatographic testing methods to improve their performance.

Aggregation-Induced Emission and Circularly Polarized Luminescence Duality in Tetracationic Binaphthyl-Based Cyclophanes

Here, we report an approach to the synthesis of highly charged enantiopure cyclophanes by the insertion of axially chiral enantiomeric binaphthyl fluorophores into the constitutions of pyridinium-based macrocycles. Remarkably, these fluorescent tetracationic cyclophanes exhibit a significant AIE compared to their neutral optically active binaphthyl precursors. A combination of theoretical calculations and time-resolved spectroscopy reveal that the AIE originates from limited torsional vibrations associated with the axes of chirality present in the chiral enantiomeric binaphthyl units and the fine-tuning of their electronic landscape when incorporated within the cyclophane structure. Furthermore, these highly charged enantiopure cyclophanes display CPL responses both in solution and in the aggregated state. This unique duality of AIE and CPL in these tetracationic cyclophanes is destined to be of major importance in future development of photonic devices and bio-applications.

Aggregation-Induced Emission (AIE) and Magnetic Resonance Imaging Characteristics for Targeted and Image-Guided siRNA Therapy of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer and remains a global health challenge. Small interfering RNA (siRNA) is a promising therapeutic modality that blocks multiple disease-causing genes without impairing cell structures. However, siRNA therapeutics still have off-target proportion and lack effective quantitative analysis method in vivo. Thus, a novel theragnostic nanoparticle with dual-mode imaging is synthesized for targeted and image-guided siRNA therapy of HCC. Survivin siRNA is carried by Poly-ethylenimine (PEI) and interacted with T7-AIE/Gd NPs, which are self-assembled of DSPE-PEG-DTPA(Gd), DSPE-PEG-Mal, DSPE-PEG-PEI, and TPE. The resulting theragnostic nanoparticles exhibit lower toxicity and high therapeutic effect, and excellent T1-weighted magnetic resonance imaging (MRI) and aggregation-induced emission (AIE) imaging performance. Moreover, in vivo MRI and AIE imaging indicate that this kind of theragnostic nanoparticles rapidly accumulates in the tumor due to active targeting and enhanced permeability and retention (EPR) effects. Sur@T7-AIE-Gd suppresses HCC tumor growth by inducing autophagy and destabilizes DNA integrity in tumor cells. The results suggest that T7-AIE-Gd nanoparticles carrying Survivin siRNA with dual-mode imaging characteristics are promising for targeted and image-guided siRNA therapy of hepatocellular carcinoma.

Synthesis of trans-stilbenes via phosphine-catalyzed coupling reactions of benzylic halides

An efficient and practical phosphine-catalyzed homo-coupling reaction of benzyl chlorides is described. The reactions proceed smoothly in the presence of CsF/B(OMe)₃ and NaH as the base, respectively, to provide trans-stilbenes in good yields with a broad scope. Unsymmetrical stilbenes are also generated from the reactions of benzyl chlorides with phosphonium salts. Several P-based key intermediates have been detected by NMR and HRMS analyses, which shed light on the postulated catalytic cycle. In the presence of different bases, the transformations involve two different pathways, in which phenylcarbene and phosphonium alkoxide are considered as key intermediates, respectively. The two pathways are complementary in synthesis but different in mechanisms. The synthetic utility, including gram-scale reactions and straightforward access to π-conjugated molecules, has been demonstrated as well.

Optical molecular imaging and theranostics in neurological diseases based on aggregation-induced emission luminogens

Optical molecular imaging and image-guided theranostics benefit from special and specific imaging agents, for which aggregation-induced emission luminogens (AIEgens) have been regarded as good candidates in many biomedical applications. They display a large Stokes shift, high quantum yield, good biocompatibility, and resistance to photobleaching. Neurological diseases are becoming a substantial burden on individuals and society that affect over 50 million people worldwide. It is urgently needed to explore in more detail the brain structure and function, learn more about pathological processes of neurological diseases, and develop more efficient approaches for theranostics. Many AIEgens have been successfully designed, synthesized, and further applied for molecular imaging and image-guided theranostics in neurological diseases such as cerebrovascular disease, neurodegenerative disease, and brain tumor, which help us understand more about the pathophysiological state of brain through noninvasive optical imaging approaches. Herein, we focus on representative AIEgens investigated on brain vasculature imaging and theranostics in neurological diseases including cerebrovascular disease, neurodegenerative disease, and brain tumor. Considering different imaging modalities and various therapeutic functions, AIEgens have great potential to broaden neurological research and meet urgent needs in clinical practice. It will be inspiring to develop more practical and versatile AIEgens as molecular imaging agents for preclinical and clinical use on neurological diseases.

Molecular Conformation Engineering To Achieve Longer and Brighter Deep Red/Near-Infrared Emission in Crystalline State

A series of molecules 1-5 containing the same fluorophore and different alkyl chains are synthesized to reveal the significant effect of molecular conformations on the emission properties. In crystalline state, molecules 1-3 exhibit strong orange emissions with maxima (λ_em) of about 600 nm and quantum yields (Φ_F) of around 60%, while molecules 4 and 5 display much longer emissions to the deep red/near-infrared (NIR) region as well as even higher efficiencies (λ_em = 693 nm, Φ_F = 73% for 4; λ_em = 654 nm, Φ_F = 93% for 5). The largely red-shifted emissions of 4 and 5 as well as the significantly improved Φ_F are very unusual. Furthermore, the Φ_F of 4 and 5 represent the highest values among organic solids with similar deep red/NIR emission wavelengths. On the basis of the experimental measurements and theoretical calculations, the new molecular design of conformation engineering, the impressive emission properties, and the potential NIR fluorescence sensing and lasing applications are comprehensively investigated.

Two-Photon Excited Near-Infrared Phosphorescence Based on Secondary Supramolecular Confinement

Organic phosphorescence materials have received wide attention in bioimaging for bio-low toxicity and large Stokes. Herein, a design strategy to achieve near-infrared (NIR) excitation and emission of organic room-temperature phosphorescence through two-stage confinement supramolecular assembly is presented. Via supramolecular macrocyclic confinement, the host-guest complexes exhibit phosphorescence with two-photon absorption (excitation wavelength up to 890 nm) and NIR emission (emission wavelength up to 800 nm) in aqueous solution, and further nano-confinement assembly significantly strengthens phosphorescence. Moreover, the nano-assemblies possess color-tunable luminescence spanning from the visible to NIR regions under different excitation wavelengths. Intriguingly, the prepared water-soluble assemblies maintain two-photon absorption and multicolor luminescence in cells or vivo.

A cell membrane-targeting AIE photosensitizer as a necroptosis inducer for boosting cancer theranostics

The exploration of cellular organelle-specific anchoring photosensitizers with both prominent fluorescence imaging behavior and extraordinary reactive oxygen species (ROS) production capability is highly in demand but remains a severe challenge for effective cancer theranostics involving photodynamic therapy (PDT). In this contribution, we developed a cell membrane-targeting and NIR-emission photosensitizer having an aggregation-induced emission (AIE) tendency. The AIE photosensitizer, namely TBMPEI, is capable of lighting up and ablating cancer cells by means of a necroptosis procedure enabling cell membrane rupture and DNA degradation upon light irradiation, endowing TBMPEI with impressive performance for both in vitro and in vivo fluorescence imaging-guided PDT.

Deep-Red Emissive Squaraine-AIEgen in Elastomer Enabling High Contrast and Fast Thermoresponse for Anti-Counterfeiting and Temperature Sensing

Two challenges remain for organic thermoresponsive materials; one is to develop high-performance red-emissive thermoresponsive materials, while another is to simultaneously achieve high contrast ratio (CR), fast and reversible thermoresponse in a single element. Herein, we not only develop a new deep-red emissive squaraine-based AIEgen (TPE-SQ12) based on a pyrylium end group, which is suitable for fabricating high-performance thermoresponsive materials, but also show an effective approach to improve both CR (∼ten times increase) and response time (less than 3 seconds), that is, molecularly dispersing AIEgen into an elastomer, attributed to the significantly expanded free volume of elastomer upon increasing the temperature that can activate the AIEgen intramolecular movements more pronouncedly. Double encryption and temperature mapping systems have been separately established by using our designed elastomer/TPE-SQ12 film, showing the great potential for anti-counterfeiting and temperature sensing. Finally, white emission is further achieved by co-doping TPE-SQ12 with cyan dye into elastomer, which enables fluorescent thermochromism for improving the temperature mapping ability.

Surfactant-Modulated a Highly Sensitive Fluorescent Probe of Fully Conjugated Covalent Organic Nanosheets for Detecting Copper Ions in Aqueous Solution

Efficient detection of aqueous copper ions is of high significance for environmental and human health, since copper is involved in potent redox activity in physiological and pathological processes. Covalent organic frameworks (COFs) have shown advantages in efficient capturing and detecting of copper ions due to their large surface area, robust chemical stability, and high sensitivity, but most of them are hydrophobic, leading to the limitation in sensing copper ions in aqueous media. Herein, the design and synthesis of an sp² -carbon conjugated COF (sp² -TPE-COF) are reported with surfactant-assisted water dispersion for detecting traces of copper ions based on the photo-induced electron transfer (PET) mechanism. Importantly, the olefin-linked conjugated backbone of sp² -TPE-COF works as a signal amplified transducer for metal ion sensing. Notably, it is found that a surfactant-assisted strategy can greatly enhance COF's dispersion in aqueous solution and finely modulate their sensitivity with a significantly improved K_SV to 15.15 × 10⁴ m^-1 in SDBS (sodium dodecyl benzene sulfonate) solution, the value of which is larger than that of a majority of COF/MOF based sensors for copper ions. This research demonstrates the promise of surfactant modulated fully π-conjugated COFs for sensing applications.

Assembly and Applications of Macrocyclic-Confinement-Derived Supramolecular Organic Luminescent Emissions from Cucurbiturils

Cucurbit[n]urils (Q[n]s or CB[n]s), as a classical of artificial organic macrocyclic hosts, were found to have excellent advantages in the fabricating of tunable and smart organic luminescent materials in aqueous media and the solid state with high emitting efficiency under the rigid pumpkin-shaped structure-derived macrocyclic-confinement effect in recent years. This review aims to give a systematically up-to-date overview of the Q[n]-based supramolecular organic luminescent emissions from the confined spaces triggered host-guest complexes, including the assembly fashions and the mechanisms of the macrocycle-based luminescent complexes, as well as their applications. Finally, challenges and outlook are provided. Since this class of Q[n]-based supramolecular organic luminescent emissions, which have essentially derived from the cavity-dependent confinement effect and the resulting assembly fashions, emerged only a few years ago, we hope this review will provide valuable information for the further development of macrocycle-based light-emitting materials and other related research fields.

Activatable Nanoprobe with Aggregation-Induced Dual Fluorescence and Photoacoustic Signal Enhancement for Tumor Precision Imaging and Radiotherapy

Owing to the high sensitivity and high spatial resolution, fluorescence (FL) imaging has been widely applied for visualizing biological processes. To gain insight into molecular events on deeper tissues, photoacoustic (PA) imaging with better deep-tissue imaging capability can be incorporated to provide complementary visualization and quantitative information on the pathological status. However, the development of activatable imaging probes to achieve both FL and PA signal amplification remains challenging because the enhancement of light absorption in PA imaging often caused the quenching of FL signal. Herein, we first developed a caspase-3 enzyme activatable nanoprobe of a nanogapped gold nanoparticle coated with AIE molecule INT20 and DEVD peptides (AuNNP@DEVD-INT20) for tumor FL and PA imaging and subsequent imaging-guided radiotherapy. The nanoprobe could interact with GSH and caspase-3 enzyme to liberate INT20 molecules, leading to AIE. Simultaneously, the in situ self-assembly of AuNPs was achieved through the cross-linking reaction between the sulfhydryl and the maleimide, resulting in ratiometric PA imaging in tumor. Remarkably, the nanoprobe can generate richful ROS for cancer radiotherapy under X-ray irradiation. The platform not only achieves the aggregation-induced FL and PA signal enhancement but also provides a general strategy for imaging of various biomarkers, eventually benefiting precise cancer therapy.

Near-Infrared Materials: The Turning Point of Organic Photovoltaics

Near-infrared (NIR)-absorbing organic semiconductors have opened up many exciting opportunities for organic photovoltaic (OPV) research. For example, new chemistries and synthetical methodologies have been developed; especially, the breakthrough Y-series acceptors, originally invented by our group, specifically Y1, Y3, and Y6, have contributed immensely to boosting single-junction solar cell efficiency to around 19%; novel device architectures such as tandem and transparent organic photovoltaics have been realized. The concept of NIR donors/acceptors thus becomes a turning point in the OPV field. Here, the development of NIR-absorbing materials for OPVs is reviewed. According to the low-energy absorption window, here, NIR photovoltaic materials (p-type (polymers) and n-type (fullerene and nonfullerene)) are classified into four categories: 700-800 nm, 800-900 nm, 900-1000 nm, and greater than 1000 nm. Each subsection covers the design, synthesis, and utilization of various types of donor (D) and acceptor (A) units. The structure-property relationship between various kinds of D, A units and absorption window are constructed to satisfy requirements for different applications. Subsequently, a variety of applications realized by NIR materials, including transparent OPVs, tandem OPVs, photodetectors, are presented. Finally, challenges and future development of novel NIR materials for the next-generation organic photovoltaics and beyond are discussed.

Development of Rofecoxib-Based Fluorophores from ACQ to AIE by Positional Regioisomerization

The development of aggregation-induced emission luminogens (AIEgens) has attracted increasing attention due to their potential applications in various areas in recent years. In this study, a facile conversion from aggregation-caused quenching (ACQ) to aggregation-induced emission (AIE) was achieved by an efficient regioisomerization strategy based on the rofecoxib scaffold. Two compounds, named PYR2 and PYR4, were identified as regioisomers of rofecoxib derivatives to show dramatically different fluorescent properties. Compound PYR2 with an ortho-substituted piperidine group showed typical AIE activity while compound PYR4 with a para-piperidine group exhibited typical ACQ behavior. Notably, compound PYR2 showed polymorphism with two forms of crystals. It was also endowed with reversible mechanochromic luminescence and acidochromic properties. The different fluorescent properties were elucidated by UV/Vis absorption spectroscopy, powder X-ray diffraction, differential scanning calorimetry, and thermogravimetric analyses. Its application as a security ink and in lipid droplets imaging have been demonstrated.