Red/NIR-Emissive Benzo[d]imidazole-Cored AIEgens: Facile Molecular Design for Wavelength Extending and In Vivo Tumor Metabolic Imaging

An in situ-activated and chemi-excited photooxygenation system based on G-poly(thioacetal) for Aβ1-42 aggregates

The abnormal aggregation of Aβ proteins, inflammatory responses, and mitochondrial dysfunction have been reported as major targets in Alzheimer's disease (AD). Photooxygenation of the amyloid-β peptide (Aβ) is viewed as a promising therapeutic intervention for AD treatment. However, the limitations of the depth of the external light source passing through the brain and the toxic side effects on healthy tissues are two significant challenges in the photooxidation of Aβ aggregates. We proposed a method to initiate the chemical stimulation of Aβ1-42 aggregate oxidation through H2O2 and correct the abnormal microenvironment of the lesions by eliminating the cascading reactions of oxidative stress. The degradable G-poly(thioacetal) undergoes cascade release of cinnamaldehyde (CA) and thioacetal triggered by endogenous H2O2, with CA in turn amplifying degradation by generating more H2O2 through mitochondrial dysfunction. A series of novel photosensitizers have been prepared and synthesized for use in the photodynamic oxidation of Aβ1-42 aggregates under white light activation. The nanoparticles (BD-6-QM/NPs) self-assembled from BD-6-QM, bis[2,4,5-trichloro-6-(pentoxycarbonyl) phenyl] ester (CPPO), and G-poly(thioacetal) not only exhibit H2O2-stimulated controlled release but also can be chemically triggered by H2O2 to generate singlet oxygen to inhibit Aβ1-42 aggregates, reducing the Aβ1-42-induced neurotoxicity.

Less is More: Asymmetric D-A Type Agent to Achieve Dynamic Self-Assembled Nanoaggregates for Long-Acting Photodynamic Therapy

To enhance the phototheranostic performance, agents with high reactive oxygen species (ROS) generation, good tumor-targeting ability, and prolonged retention are urgently needed. However, symmetric donor-acceptor (D-A) type agents usually produce spherical nanoaggregates, leading to good tumor targeting but inferior retention. Rod-like nanoaggregates are desired to extend their retention in tumors; however, this remains a challenge. In particular, agents with dynamically changeable shapes that integrate merits of different morphologies are seldomly reported. Therefore, self-assembled organic nanoaggregates with smart shape tunability are designed here using an asymmetric D-A type TIBT. The photoluminescence quantum yield in solids is up to 52.24% for TIBT. TIBT also exhibits high ROS generation in corresponding nanoaggregates (TIBT-NCs). Moreover, dynamic self-assembly in shape changing from nanospheres to nanorods occurrs in TIBT-NCs, contributing to the enhancement of ROS quantum yield from 0.55 to 0.72. In addition, dynamic self-assembly can be observed for both in vitro and in vivo, conferring TIBT-NCs with strong tumor targeting and prolonged retention. Finally, efficient photodynamic therapy to inhibit tumor growth is achieved in TIBT-NCs, with an inhibition rate of 90%. This work demonstrates that asymmetric D-A type agents can play significant roles in forming self-assembled organic nanoaggregates, thus showing great potential in long-acting cancer therapy.

Bioconjugation and Reaction-Induced Tumor Therapy via Alkynamide-Based Thiol-Yne Click Reaction

Ferroptosis is associated with the occurrence and development of many diseases, which is the result of an imbalance in cellular metabolism and oxidation-reduction balance. Therefore, it is an effective therapeutic strategy that simultaneously regulating the intracellular oxidation-reduction system. Herein, a click reaction of alkynylamide with thiol groups in the presence of amine or in PBS (pH = 7.4) is developed, which can react efficiently with thiol substances, such as cysteine (Cys), glutathione (GSH), and bovine serum albumin (BSA). Notably, MBTB-PA, an aggregation-induced emission (AIE) photosensitizer with an alkynylamide unit, is synthesized and its intracellular behavior is visualized in situ by fluorescence imaging, demonstrating its excellent ability to target the endoplasmic reticulum. Furthermore, MBTB-PA reacted with proteins in tumor cells, consumed reducing substances, and triggered intracellular oxidative stress, resulting in cell death. Based on this reaction therapy strategy, click reaction is combined with photodynamic therapy to achieve effective killing of tumor cells by simultaneously raising the intracellular oxidative state and reducing the reductive state. This work not only develops an application of click reaction of alkynamide with thiol in bioconjugation and anti-tumor therapy, but also provides feasible ideas for organic reactions in the exploration of organisms.

Enzyme-Mediated Bioorthogonal Cascade Catalytic Reaction for Metabolism Intervention and Enhanced Ferroptosis on Neuroblastoma

It remains a tremendous challenge to explore effective therapeutic modalities against neuroblastoma, a lethal cancer of the sympathetic nervous system with poor prognosis and disappointing treatment outcomes. Considering the limitations of conventional treatment modalities and the intrinsic vulnerability of neuroblastoma, we herein develop a pioneering sequential catalytic therapeutic system that utilizes lactate oxidase (LOx)/horseradish peroxidase (HRP)-loaded amorphous zinc metal-organic framework, named LOx/HRP-aZIF, in combination with a 3-indole-acetic acid (IAA) prodrug. On the basis of abnormal lactate accumulation that occurs in the tumor microenvironment, the cascade reaction of LOx and HRP consumes endogenous glutathione and a reduced form of nicotinamide adenine dinucleotide to achieve the first stage of killing cancer cells via antioxidative incapacitation and electron transport chain interference. Furthermore, the generation of reactive oxygen species induced by HRP and IAA through bioorthogonal catalysis promotes ferritin degradation and lipid peroxidation, ultimately provoking self-enhanced ferroptosis with positive feedback by initiating an endogenous Fenton reaction. This work highlights the superiority of the natural enzyme-dependent cascade and bioorthogonal catalytic reaction, offering a paradigm for synergistically enzyme-based metabolism-ferroptosis anticancer therapy.

In Situ Glycan Analysis and Editing in Living Systems

Besides proteins and nucleic acids, carbohydrates are also ubiquitous building blocks of living systems. Approximately 70% of mammalian proteins are glycosylated. Glycans not only provide structural support for living systems but also act as crucial regulators of cellular functions. As a result, they are considered essential pieces of the life science puzzle. However, research on glycans has lagged far behind that on proteins and nucleic acids. The main reason is that glycans are not direct products of gene coding, and their synthesis is nontemplated. In addition, the diversity of monosaccharide species and their linkage patterns contribute to the complexity of the glycan structures, which is the molecular basis for their diverse functions. Research in glycobiology is extremely challenging, especially for the in situ elucidation of glycan structures and functions. There is an urgent need to develop highly specific glycan labeling tools and imaging methods and devise glycan editing strategies. This Perspective focuses on the challenges of in situ analysis of glycans in living systems at three spatial levels (i.e., cell, tissue, and in vivo) and highlights recent advances and directions in glycan labeling, imaging, and editing tools. We believe that examining the current development landscape and the existing bottlenecks can drive the evolution of in situ glycan analysis and intervention strategies and provide glycan-based insights for clinical diagnosis and therapeutics.

Multimodal Therapeutic Platforms Based on Self-Assembled Metallacycles/Metallacages for Cancer Radiochemotherapy

Discrete organometallic complexes with defined structures are proceeding rapidly in combating malignant tumors due to their multipronged treatment modalities. Many innovative superiorities, such as high antitumor activity, extremely low systemic toxicity, active targeting ability, and enhanced cellular uptake, make them more competent for clinical applications than individual precursors. In particular, coordination-induced regulation of luminescence and photophysical properties of organic light-emitting ligands has demonstrated significant potential in the timely evaluation of therapeutic efficacy by bioimaging and enabled synergistic photodynamic therapy (PDT) or photothermal therapy (PTT). This review highlights instructive examples of multimodal radiochemotherapy platforms for cancer ablation based on self-assembled metallacycles/metallacages, which would be classified by functions in a progressive manner. Finally, the essential demands and some plausible prospects in this field for cancer therapy are also presented.

Beyond traditional light: NIR-II light-activated photosensitizers for cancer therapy

With increasing demand for the accurate and safe treatment of cancer, non-invasive photodynamic therapy (PDT) has received widespread attention. However, most conventional photosensitizers are typically excited by short-wavelength visible light (400-700 nm), thus substantially hindering the penetration of light and the therapeutic effectiveness of the PDT procedure. Fortunately, near-infrared (NIR) light (>700 nm), in particular, light in the second near-infrared region (NIR-II, 1000-1700 nm) has a higher upper radiation limit, greater tissue tolerance, and deeper tissue penetration compared with traditional short-wavelength light excitation, and shows considerable potential in the clinical treatment of cancer. Therefore, it is of paramount importance and clinical value to develop photosensitizers that are excited by NIR-II light. In this review, for the first time we focus completely on recent progress made with various NIR-II photosensitizers for cancer treatment via PDT, and we briefly present the ongoing challenges and prospects of currently developed NIR-II photosensitizers for clinical practice in the near future. We believe that the above topics will inspire broad interest in researchers from interdisciplinary fields that include chemistry, materials science, pharmaceuticals, and clinical medicine, and provide insightful perspectives for exploiting new NIR-II photosensitizers for biomedical applications.

Natural protoberberine alkaloid-montmorillonite nanocomposite powders with AIE features for visualizing high-resolution latent fingerprints

Real-time and in-situ fluorescence visualization technologies have attention to in the forensic analysis of latent fingerprints (LFPs). The fingerprint powders with high performance and biocompatibility are essential for imaging LFPs with high definition and safety. In this work, five quaternary protoberberine alkaloid (QPA) derivatives were analyzed with reorganization energy and four-point calculations to explain the relationship between the substituent effect and luminescent properties and further resolve the luminous behaviors of four QPA-based natural products in solution. Thanks to the restriction of the intramolecular motions mechanism, aggregation-induced emission (AIE) active BBC nanoaggregates could sensitively detect explosive analog, 2,4,6-trinitrophenol, at a nanomolar level (9.8 nM of detection limit). Combined with natural montmorillonite (MMT) mineral powders, three levels of details for fingerprints were successfully imaged with solid-luminous BBC/MMT nanocomposites. The insight into the substituted effect of alkoxy groups on the QPA framework not only provides a new concept to design rotor-free AIE luminogens but also expands natural products and their nanocomposites into LFP and detection applications.

In Vivo Fluorescence Imaging-Guided Development of Near-Infrared AIEgens

In vivo fluorescence imaging has received extensive attention due to its distinguished advantages of excellent biosafety, high sensitivity, dual temporal-spatial resolution, real-time monitoring ability, and non-invasiveness. Aggregation-induced emission luminogens (AIEgens) with near-infrared (NIR) absorption and emission wavelengths are ideal candidate for in vivo fluorescence imaging for their large Stokes shift, high brightness and superior photostability. NIR emissive AIEgens provide deep tissue penetration depth as well as low interference from tissue autofluorescence. Here in this review, we summarize the molecular engineering strategies for constructing NIR AIEgens with high performances, including extending π-conjugation system and strengthen donor (D)-acceptor (A) interactions. Then the encapsulation strategies for increasing water solubility and biocompatibility of these NIR AIEgens are highlighted. Finally, the challenges and prospect of fabricating NIR AIEgens for in vivo fluorescence imaging are also discussed. We hope this review would provide some guidelines for further exploration of new NIR AIEgens.

Tuning the Cellular Uptake and Retention of Rhodamine Dyes by Molecular Engineering for High-Contrast Imaging of Cancer Cells

Probes allowing high-contrast discrimination of cancer cells and effective retention are powerful tools for the early diagnosis and treatment of cancer. However, conventional small-molecule probes often show limited performance in both aspects. Herein, we report an ingenious molecular engineering strategy for tuning the cellular uptake and retention of rhodamine dyes. Introduction of polar aminoethyl leads to the increased brightness and reduced cellular uptake of dyes, and this change can be reversed by amino acetylation. Moreover, these modifications allow cancer cells to take up more dyes than normal cells (16-fold) through active transport. Specifically, we further improve the signal contrast (56-fold) between cancer and normal cells by constructing activatable probes and confirm that the released fluorophore can remain in cancer cells with extended time, enabling long-term and specific tumor imaging.

Full-Color Emissive D-D-A Carbazole Luminophores: Red-to-NIR Mechano-fluorochromism, Aggregation-Induced Near-Infrared Emission, and Application in Photodynamic Therapy

The preparation of multifunctionalized luminophores with full-color emission based on an identical core skeleton is a significative but challenging research topic. In this work, eight donor-donor-acceptor (D-D-A)-type luminogens based on a central carbazole core bearing a C₆ hydrocarbon chain were designed by using different kinds of donor and acceptor units on the left and right, and synthesized in good yields. These D-D-A carbazole derivatives display deep-blue, sky-blue, cyan, green, yellow-green, yellow, orange and red fluorescence in the solid state, achieving full-color emission covering the whole visible light range under UV light illumination. Notably, the dicyano-functionalized triphenylamine-containing carbazole derivative exhibits rare aggregation-induced near-infrared emission and red-to-near-infrared mechano-fluorochromism with high contrast beyond 100 nm. Furthermore, the red-emissive luminogen can serve as a potential candidate for cell imaging and photodynamic therapy (PDT). This work not only provides reference for the construction of full-color emissive systems but also opens a new avenue to the preparation of multifunctionalized luminophores capable of simultaneous application in near-Infrared mechanical-force sensors and PDT fields.

AIEgens/Mitochondria Nanohybrids as Bioactive Microwave Sensitizers for Non-Thermal Microwave Cancer Therapy

Aggregation-induced emission luminogens (AIEgens) are widely used as photosensitizers for image-guided photodynamic therapy (PDT). Due to the limited penetration depth of light in biological tissues, the treatments of deep-seated tumors by visible-light-sensitized aggregation-induced emission (AIE) photosensitizers are severely hampered. Microwave dynamic therapy attracts much attention because microwave irradiation can penetrate very deep tissues and sensitize the photosensitizers to generate reactive oxygen species (ROS). In this work, a mitochondrial-targeting AIEgen (DCPy) is integrated with living mitochondria to form a bioactive AIE nanohybrid. This nanohybrid can not only generate ROS under microwave irradiation to induce apoptosis of deep-seated cancer cells but also reprogram the metabolism pathway of cancer cells through retrieving oxidative phosphorylation (OXPHOS) instead of glycolysis to enhance the efficiency of microwave dynamic therapy. This work demonstrates an effective strategy to integrate synthetic AIEgens and natural living organelles, which would inspire more researchers to develop advanced bioactive nanohybrids for cancer synergistic therapy.

Ion Transport in 2D Nanostructured π-Conjugated Thieno[3,2-b]thiophene-Based Liquid Crystal

Leveraging the self-assembling behavior of liquid crystals designed for controlling ion transport is of both fundamental and technological significance. Here, we have designed and prepared a liquid crystal that contains 2,5-bis(thien-2-yl)thieno[3,2-b]thiophene (BTTT) as mesogenic core and conjugated segment and symmetric tetra(ethylene oxide) (EO4) as polar side chains for ion-conducting regions. Driven by the crystallization of the BTTT cores, BTTT/dEO4 exhibits well-ordered smectic phases below 71.5 °C as confirmed by differential scanning calorimetry, polarized optical microscopy, temperature-dependent wide-angle X-ray scattering, and grazing incidence wide-angle X-ray scattering (GIWAXS). We adopted a combination of experimental GIWAXS and molecular dynamics (MD) simulations to better understand the molecular packing of BTTT/dEO4 films, particularly when loaded with the ion-conducting salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Ionic conduction of BTTT/dEO4 is realized by the addition of LiTFSI, with the material able to maintain smectic phases up to r = [Li⁺]/[EO] = 0.1. The highest ionic conductivity of 8 × 10^-3 S/cm was attained at an intermedium salt concentration of r = 0.05. It was also found that ion conduction in BTTT/dEO4 is enhanced by forming a smectic layered structure with irregular interfaces between the BTTT and EO4 layers and by the lateral film expansion upon salt addition. This can be explained by the enhancement of the misalignment and configurational entropy of the side chains, which increase their local mobility and that of the solvated ions. Our molecular design thus illustrates how, beyond the favorable energetic interactions that drive the assembly of ion solvating domains, modulation of entropic effects can also be favorably harnessed to improve ion conduction.

Carbazole-based aggregation-induced phosphorescent emission-active gold(I) complexes with various phosphorescent mechanochromisms

A series of carbazole-containing gold(I) complexes modified with different substituents were successfully designed and synthesized, and their molecular structures were characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. The aggregation-induced behaviors of these gold(I) complexes were studied by ultraviolet/visible and photoluminescence spectroscopy. Meanwhile, their mechanical force-responsive emissive properties were also investigated via solid-state photoluminescence spectroscopy. Interestingly, all these gold(I)-based luminogenic molecules were capable of exhibiting aggregation-induced phosphorescent emission phenomena. Furthermore, their solids of three gold(I) complexes displayed contrasting mechano-responsive phosphorescence features. More specifically, trifluoromethyl or methoxyl-substituted luminophores 1 and 3 demonstrated mechanochromic behaviors involving blue-shifted phosphorescence changes, and their mechanoluminochromic phenomena were reversible. However, the solid-state phosphorescence of phenyl-substituted luminophor 2 was not sensitive to external mechanical force.

Morpholine-Functionalized Multicomponent Metallacage as a Vector for Lysosome-Targeted Cell Imaging

Metallacages with suitable cavities and specific functions are promising delivery vectors in biological systems. Herein, we report a morpholine-functionalized metallacage for lysosome-targeted cell imaging. The efficient host-guest interactions between the metallacage and dyes prevent them from aggregation, so their emission in aqueous solutions is well maintained. The fluorescence quantum yield of these host-guest complexes reaches 74.40%. Therefore, the metallacage is further employed as a vector to deliver dyes with different emission colors (blue, green, and red) into lysosomes for targeted imaging. This research affords a type of vector for the delivery of various cargos toward biological applications, which will enrich the usage of metallacages in biomedical engineering.

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.

Metal-free bioorthogonal click chemistry in cancer theranostics

Bioorthogonal chemistry is a powerful tool to site-specifically activate drugs in living systems. Bioorthogonal reactions between a pair of biologically reactive groups can rapidly and specifically take place in a mild physiological milieu without perturbing inherent biochemical processes. Attributed to their high selectivity and efficiency, bioorthogonal reactions can significantly decrease background signals in bioimaging. Compared with metal-catalyzed bioorthogonal click reactions, metal-free click reactions are more biocompatible without the metal catalyst-induced cytotoxicity. Although a great number of bioorthogonal chemistry-based strategies have been reported for cancer theranostics, a comprehensive review is scarce to highlight the advantages of these strategies. In this review, recent progress in cancer theranostics guided by metal-free bioorthogonal click chemistry will be depicted in detail. The elaborate design as well as the advantages of bioorthogonal chemistry in tumor theranostics are summarized and future prospects in this emerging field are emphasized.

Well-defined polyacrylamides with AIE properties via rapid Cu-mediated living radical polymerization in aqueous solution: thermoresponsive nanoparticles for bioimaging

There is a requirement for the development of methods for the preparation of well-controlled polymers with aggregation-induced emission (AIE) properties.

Development of nanotechnology-mediated precision radiotherapy for anti-metastasis and radioprotection

Radiotherapy (RT), including external beam RT and internal radiation therapy, uses high-energy ionizing radiation to kill tumor cells.

Design and Structural Regulation of AIE photosensitizers for imaging-guided photodynamic anti-tumor application

In recent years, photodynamic therapy (PDT) has become one of the important therapeutic methods for treating cancer. Aggregation-induced emission (AIE) photosensitizers (PSs) overcome the aggregation-caused quenching (ACQ) effects of conventional...

Acceptor engineering of small-molecule fluorophores for NIR-II fluorescence and photoacoustic imaging

Fluorescence imaging in the second near-infrared window (NIR-II) has been an emerging technique in diverse in vivo applications with high sensitivity/resolution and deep tissue penetration. To date, the design principle of the reported NIR-II organic fluorophores has heavily relied on benzo[1,2-c:4,5-c']bis([1,2,5]thiadiazole) (BBTD) as a strong electron acceptor. Here, we report the rational design and synthesis of a NIR-II fluorescent molecule with the rarely used [1,2,5]thiadiazolo[3,4-f]benzotriazole (TBZ) core to replace BBTD as the electron acceptor. Thanks to the weaker electron deficiency of the TBZ core than BBTD, the newly yielded NIR-II molecule (BTB) based nanoparticles have a higher mass extinction coefficient and quantum yield in water. In contrast, the nanoparticle suspension of its counterpart with BBTD as the core is nearly nonemissive. The NIR-II BTB nanoparticles allow video-rate fluorescence imaging for vasculature imaging in ears, hindlimbs, and the brain of the mouse. Additionally, its large absorptivity in the NIR-I region also promotes bioimaging using photoacoustic microscopy (PAM) and tomography (PAT). Upon surface conjugation with the Arg-Gly-Asp (RGD) peptide, the functionalized nanoparticles ensured targeted detection of integrin-overexpressed tumors through both imaging modalities in two- and three-dimensional views. Thus, our approach to engineering acceptors of organic fluorophores offers a promising molecular design strategy to afford new NIR-II fluorophores for versatile biomedical imaging applications.

Surfactant-Stripped Micelles with Aggregation-Induced Enhanced Emission for Bimodal Gut Imaging In Vivo and Microbiota Tagging Ex Vivo

Aggregation-induced emission luminogens (AIEgens) hold promise for biomedical imaging and new approaches facilitating their aggregation state are desirable for fluorescence enhancement. Herein, a series of surfactant-stripped AIEgen micelles (SSAMs) with improved fluorescence are developed by a low-temperature surfactant-stripping method to encapsulate AIEgens in temperature-sensitive Pluronic block copolymer. After stripping excessive surfactant, SSAMs exhibit altered optical properties and significantly higher fluorescence quantum yield. Using this method, a library of highly concentrated fluorescent nanoparticles are generated with tunable absorption and emission wavelengths, permitting imaging of deep tissues at different wavelengths. SSAMs remain physiologically stable and can pass safely through gastrointestinal tract (GI) without degradation in the harsh conditions, allowing for fluorescence and photoacoustic imaging of intestine with high resolution. d-amino acids (DAA), a natural metabolite for bacteria, can be chemically conjugated on the surface of SSAMs, enabling non-invasive monitoring of the microbial behavior of ex vivo fluorescently labeled gut microbiota in the GI tract.

Aggregation-Induced Emission Luminogens with Photoresponsive Behaviors for Biomedical Applications

Fluorescent biomedical materials can visualize subcellular structures and therapy processes in vivo. The aggregation-induced emission (AIE) phenomenon helps suppress the quenching effect in the aggregated state suffered by conventional fluorescent materials, thereby contributing to design strategies for fluorescent biomedical materials. Photoresponsive biomedical materials have attracted attention because of the inherent advantages of light; i.e., remote control, high spatial and temporal resolution, and environmentally friendly characteristics, and their combination with AIE facilitates development of fluorescent molecules with efficient photochemical reactions upon light irradiation. In this review, organic compounds with AIE features for biomedical applications and design strategies for photoresponsive AIE luminogens (AIEgens) are first summarized briefly. Applications are then reviewed, with the employment of photoresponsive and AIE-active molecules for photoactivation imaging, super-resolution imaging, light-induced drug delivery, photodynamic therapy with photochromic behavior, and bacterial targeting and killing being discussed at length. Finally, the future outlook for AIEgens is considered with the aim of stimulating innovative work for further development of this field.

NIR-II Fluorescent Brightness Promoted by "Ring Fusion" for the Detection of Intestinal Inflammation

Fluorophores with emission in the second near-infrared window (NIR-II) have displayed salient advantages for biomedical applications. However, the common strategy of reducing the energy bandgap of fluorophores so as to achieve red-shifted wavelengths always leads to compromised fluorescent brightness. Herein, we propose a molecular design concept of "ring-fusion" to modify the acceptor of AIEgen that can extend the luminous wavelength from NIR-I to NIR-II. The fused-acceptor-containing fluorophore yielded, TTQP, has an enhanced absorption coefficient with a higher brightness in nanoparticle formation compared to its NIR-I emissive counterpart (TTQ-DP) with a non-fused acceptor. Theoretical calculation further confirms that the ring fusion can efficiently promote the rigidity and planarity of the electron-deficient core, leading to a lower reorganization energy and nonradiative decay. The TTQP NPs yielded thus allow sensitive NIR-II fluorescence imaging of vasculature and intestinal inflammation in mice models. Therefore, we anticipate that our work will provide a promising molecular-engineering strategy to enrich the library and broaden the application scope of NIR-II fluorophores.

Theoretical Simulations of Thermochromic and Aggregation-Induced Emission Behaviors of a Series of Red-Light Anthracene-o-carborane Derivatives

Quantum mechanical and molecular dynamics simulations have been carried out on a series of anthracene-o-carborane derivatives (ANT-H, ANT-Ph, ANT-Me and ANT-TMS) with rare red-light emission in the solid state. The simulation of the heating process of the crystals and further comparison of the molecular structures and excited-state properties before and after heating help us to disclose the thermochromic behavior, that is, the red-shift emission is caused by elongation of the C1-C2 bond in the carborane moiety after heating. Thus, we believe that the molecular structure in the crystal is severely affected by heating. Transformation of the molecular conformation appears in the ANT-H crystal with increasing temperature. More specifically, the anthracene moiety moves from nearly parallel to the C1-C2 bond to nearly perpendicular, causing the short-wavelength emission to disappear after heating. As for the aggregation-induced emission phenomenon, the structures and photophysical properties were investigated comparatively in both the isolated and crystal states; the results suggested that the energy dissipation in crystal surroundings was greatly reduced through hindering structure relaxation from the excited to the ground state. We expect that discussion of the thermochromic behavior will provide a new analysis perspective for the molecular design of o-carborane derivatives.

One-for-All Phototheranostic Agent Based on Aggregation-Induced Emission Characteristics for Multimodal Imaging-Guided Synergistic Photodynamic/Photothermal Cancer Therapy

Phototheranostics represents a promising direction for modern precision medicine, which has recently received considerable attention for cancer research. The ingenious integration of all phototheranostic modalities in a single molecule with precise spatial colocalization is a tremendously challenging task, which mainly arises from the complexity of molecular design and energy dissipation. Reports on a single molecular one-for-all theranostic agent are still very rare. Herein, we designed two novel aggregation-induced emission (AIE)-active fluorogens (AIEgens, named DPMD and TPMD) with a cross-shaped donor-acceptor structure via a facile synthetic method and constructed versatile nanoparticles (NPs) by encapsulating AIEgen with an amphiphilic polymer. The AIEgen TPMD with a twisted structure, high donor-acceptor (D-A) strength, small singlet-triplet energy gap, and abundant intramolecular rotators and vibrators was selected as an ideal candidate for balancing and utilizing the radiative and nonradiative energy dissipations. Notably, TPMD NPs simultaneously possess adequate near-infrared (NIR) fluorescence emission at 821 nm for fluorescence imaging, effective reactive oxygen species generation for photodynamic therapy (PDT), and outstanding photothermal effect for photoacoustic imaging, photothermal imaging, and photothermal therapy (PTT), which demonstrates the superior potential of AIE NPs in multimodal imaging-guided synergistic PDT/PTT therapy.

Bioorthogonal Pretargeting Strategy for Anchoring Activatable Photosensitizers on Plasma Membranes for Effective Photodynamic Therapy

Developing novel activatable photosensitizers with excellent plasma membrane targeting ability is urgently needed for smart photodynamic therapy (PDT). Herein, a tumor acidity-activatable photosensitizer combined with a two-step bioorthogonal pretargeting strategy to anchor photosensitizers on the plasma membrane for effective PDT is developed. Briefly, artificial receptors are first anchored on the cell plasma membrane using cell-labeling agents (Az-NPs) via the enhanced permeability and retention effect to achieve the tumor cell labeling. Then, pH-sensitive nanoparticles (S-NPs) modified with dibenzocyclooctyne (DBCO) and chlorin e6 (Ce6) accumulate in tumor tissue and disassemble upon protonation of their tertiary amines in response to the acidic tumor environment, exposing the contained DBCO and Ce6. The selective, highly specific click reactions between DBCO and azide groups enable Ce6 to be anchored on the tumor cell surface. Upon laser irradiation, the cell membrane is severely damaged by the cytotoxic reactive oxygen species, resulting in remarkable cellular apoptosis. Taken together, the membrane-localized PDT by our bioorthogonal pretargeting strategy to anchor activatable photosensitizers on the plasma membrane provides a simple but effective method for enhancing the therapeutic efficacy of photosensitizers in anticancer therapy.

Acceptor Engineering for Optimized ROS Generation Facilitates Reprogramming Macrophages to M1 Phenotype in Photodynamic Immunotherapy

Reprogramming tumor-associated macrophages to an antitumor M1 phenotype by photodynamic therapy is a promising strategy to overcome the immunosuppression of tumor microenvironment for boosted immunotherapy. However, it remains unclear how the reactive oxygen species (ROS) generated from type I and II mechanisms, relate to the macrophage polarization efficacy. Herein, we design and synthesize three donor-acceptor structured photosensitizers with varied ROS-generating efficiencies. Surprisingly, we discovered that the extracellular ROS generated from type I mechanism are mainly responsible for reprogramming the macrophages from a pro-tumor type (M2) to an anti-tumor state (M1). In vivo experiments prove that the photosensitizer can trigger photodynamic immunotherapy for effective suppression of the tumor growth, while the therapeutic outcome is abolished with depleted macrophages. Overall, our strategy highlights the designing guideline of macrophage-activatable photosensitizers.

Supramolecular ensembles modified by near-infrared dyes and their biological applications

Near-infrared dyes possess the qualities of lower interference with biological autofluorescence, low photon scattering, and deep tissue penetration, and are being increasingly involved in the development of biomaterials for sensing and precision medicine. However, dyes usually suffer from the disadvantages of poor water solubility and photobleaching, factors that limit their application in vivo. The introduction of supramolecular ensembles can provide an ideal solution. This review presents recently developed supramolecular ensembles modified by near-infrared dyes. Compared with small-molecule fluorophores, the specific size of a supramolecular-based fluorophore endows it with longer circulation time in the bloodstream, increasing its chances of reaching a specific target. In addition, the construction of supramolecule-based fluorophores with versatile functions can be achieved by simple encapsulation or doping, instead of by complicated chemical synthesis. Thus, supramolecular-complex-based fluorophores offer high potential in diagnosis and therapy. This review outlines four different species of near-infrared dye based ensembles in terms of their method of formation, including simple encapsulation or doping and copolymerisation. Recently, a new technology has employed modified fluorophores for in situ self-assembly that form supramolecular ensembles at a specific position, thus solving the problem of poor uptake of nanoparticles by cells, and is included in this review. Finally, the future of this field is considered.

The Aggregation Regularity Effect of Multiarylpyrroles on Their Near-Infrared Aggregation-Enhanced Emission Property

Increasing the quantum yield of near-infrared (NIR) emissive dyes is critical for biological applications because these fluorescent dyes generally show decreased emission efficiency under aqueous conditions. In this work, we designed and synthesized several multiarylpyrrole (MAP) derivatives, in which a furanylidene (FE) group at the 3-position of the pyrrole forms donor-π-acceptor molecules, MAP-FE, with a NIR emissive wavelength and aggregation-enhanced emission (AEE) features. Different alkyl chains of MAP-FEs linked to phenyl groups at the 2,5-position of the pyrrole ring resulted in different emissive wavelengths and quantum yields in aggregated states, such as powders or single crystals. Powder XRD data and single crystal analysis elucidated that the different lengths of alkyl chains had a significant impact on the regularity of MAP-FEs when they were forced to aggregate or precipitate, which affected the intermolecular interaction and the restriction degree of the rotating parts, which are essential components. Therefore, an increasing number of NIR dyes could be developed by this design strategy to produce efficient NIR dyes with AEE. Moreover, this method can provide general guidance for other related fields, such as organic solar cells and organic light-emitting materials, because they are all applied in the aggregated state.

Morphological Evolution of Strongly Fluorescent Water Soluble AIEEgen-Triblock Copolymer Mixed Aggregates with Shape-Dependent Cell Permeability

Dimethyl-2,5-bis(4-methoxyphenylamino)terephthalate (DBMPT) is a water-insoluble fluorogenic molecule, which has been rendered water-soluble in physiological conditions, by the addition of triblock copolymers (TBPs), P123 (PEO₁₉PPO₆₉PEO₁₉), and F127 (PEO₁₀₀PPO₆₅PEO₁₀₀). DBMPT-TBP mixed aggregates, formed in the process, exhibit significant aggregation-induced enhancement of emission, with nanosecond fluorescence lifetimes. Dynamics involved in suppression of nonradiative pathways and consequent enhancement of fluorescence are followed by femtosecond transient absorption and time-resolved fluorescence spectroscopic techniques. Interestingly, shapes of the aggregates formed with the two TBPs are found to be very different, even though they differ only in the length of hydrophilic blocks. DBMPT-P123 aggregates are micrometer-sized and spherical, while DBMPT-F127 aggregates form nanorods. Evolution of their morphologies, as a function of TBP concentration, is monitored using cryo-TEM, FESEM, and fluorescence lifetime imaging microscopy. Fluorescence lifetime distribution provides useful insight into microheterogeneity in these mixed aggregates. Excellent cell permeability is observed for DBMPT-F127 nanorods, in contrast to DBMPT-P123 microspheres. These fluorescent nanorods exhibit the ability to mark lipid droplets within the cell and hence bear the promise for application in intracellular imaging.

Encapsulation-Dependent Enhanced Emission of Near-Infrared Nanoparticles Using in vivo Three-Photon Fluorescence Imaging

We discovered a unique fluorescent enhancement of dye encapsulated polymeric nanoparticles, which strongly depended on the polymeric matrix. Interestingly, the polymer nanoparticles containing a NIR emissive dye exhibited remarkable enhancement of emission encapsulated by the polymer amphiphilic polymer containing polystyrene (PS) moiety, whereas the nanoparticles showed weak fluorescence when using other polymer encapsulation. The highest fluorescent quantum yield of nanoparticles can reach 27% by using PS-PEG encapsulation, where the strong NIR fluorescence can be observed. These ultra-bright fluorescence nanoparticles also possess a strong three-photon fluorescence and show a good candidate for in vivo vascular three-photon fluorescence imaging of mouse brain and ear under 1550 nm fs laser excitation. A fine three-dimensional (3D) reconstruction with an imaging depth of 635 and 180 μm was achieved, respectively. We further demonstrate that these nanoparticles can effectively target the sentinel lymph node (SLN) of mice.

Fluorescent nanoparticles with ultralow chromophore loading for long-term tumor-targeted imaging

Recently, organic dyes with aggregation-induced emission (AIE) have attracted much attention in bioimaging and diagnostics. Relatively, the application of traditional dyes has diminished because of aggregation-caused quenching (ACQ). In this work, we compare the imaging ability of nanoparticle formulations of these two kinds of dyes. Boron dipyrromethene (BODIPY) was chosen as a representative of the ACQ dyes, and an aggregation-induced emission (AIE) dye BPMT was used for comparison. BODIPY and BPMT were entrapped into PEG_5k-PLA_10k to form BODIPY-loaded NPs (BNPs) and BPMT-loaded NPs (ANPs), respectively. In vivo and ex vivo imaging demonstrated that BNP1 with ultralow BODIPY load (0.07%) can effectively accumulate in tumor tissues and enable long-term noninvasive imaging. In contrast, ANP4 with high BPMT load (1.6%) has poor bioimaging ability. In general, our work has certain reference significance for the application of ACQ dyes and AIEgens in bioimaging, diagnostics, and theranostics. STATEMENT OF SIGNIFICANCE: In this work, Boron dipyrromethene (BODIPY) was chosen as a representative of ACQ dyes. As a control, (Z)-2-(4'-(9H-carbazol-9-yl)-[1,1'-biphenyl]-4-yl)-3-(7-(4-(bis(4methoxyphenyl)amino) phenyl) benzo[c] [1,2,5] thiadiazol-4-yl) acrylonitrile (BPMT) was selected as an aggregation-induced emission (AIE) dye. BODIPY and BPMT was entrapped into PEG5k-PLA10k to form BODIPY-loaded NPs (BNPs) and BPMT-loaded NPs (ANPs), respectively. In vivo and ex vivo imaging demonstrated that BNP1 with ultralow BODIPY load (0.07%) can effectively accumulate in tumor tissues and realize long-term noninvasive imaging. The weaknesses of ACQ effect can be converted into advantages by skillful use of nanotechnology, which can not only save the cost but also realize high efficiency targeted cancer imaging.

A Fluorescence-Phosphorescence-Phosphorescence Triple-Channel Emission Strategy for Full-Color Luminescence

Organic luminogens constitute promising prototypes for various optoelectronic applications. Since gaining distinct color emissions normally requires the alternation of the conjugated backbone, big issues remain in material synthetic cost and skeleton compatibility while pursuing full-color luminescence. Upon a facile one-step coupling, three simple but smart perchalcogenated (O, S, and Se) arenes are synthesized. They exhibit strong luminescent tricolor primaries (i.e., blue, green, and red, respectively) in the solid state with a superior quantum yield up to >40% (5-10 times higher than that in corresponding solutions). The properties originate from a fluorescence-phosphorescence-phosphorescence triple-channel emission effect, which is regulated by S and Se heavy atoms-dependent intersystem crossing upon molecular packing, as well as Se-Se atom interaction-caused energy splittings. Consequently, full-color luminescence, including a typical white-light luminescence with a Commission Internationale de I'Eclairage coordinate of (0.30, 0.35), is realized by complementarily incorporating these tricolor luminescent materials in the film. Moreover, mechanochromic luminescent color conversions are also observed to achieve the fine-tuning of the luminescent tints. This strategy can be smart to address full-color luminescence on the same molecular skeleton, showing better material compatibility as an alternative to the traditional multiple-luminophore engineering.