Cobalt-Catalyzed Cascade C-H Activation/Annulation Polymerizations toward Diversified and Multifunctional Sulfur-Containing Fused Heterocyclic Polymers.

Transition-metal-catalyzed C-H activation has greatly benefited the synthesis and development of functional polymer materials, and the construction of multifunctional fused (hetero)cyclic polymers via novel C-H activation-based polyannulations has emerged as a charming but challenging area in recent years. Herein, we report the first cobalt(III)-catalyzed cascade C-H activation/annulation polymerization (CAAP) approach that can efficiently transform readily available aryl thioamides and internal diynes into multifunctional sulfur-containing fused heterocyclic (SFH) polymers. Within merely 3 h, a series of SFH polymers bearing complex and multisubstituted S,N-doped polycyclic units are facilely and efficiently produced with high molecular weights (absolute Mn up to 220400) in excellent yields (up to 99%), which are hard to achieve by traditional methods. The intermediate-terminated SFH polymer can be used as a reactive macromonomer to controllably extend or modify polymer main chains. The structural diversity can be further enriched through facile S-oxidation and N-methylation reactions of the SFH polymers. Benefiting from the unique structures, the obtained polymers exhibit excellent solution processability, high thermal and morphological stability, efficient and readily tunable aggregate-state fluorescence, stimuli-responsive properties, and high and UV-modulatable refractive indices of up to 1.8464 at 632.8 nm. These properties allow the SFH polymers to be potentially applied in diverse fields, including metal ion detection, photodynamic killing of cancer cells, fluorescent photopatterning, and gradient-index optical materials.

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.

Click-Reaction-Mediated Chemotherapy and Photothermal Therapy Synergistically Inhibit Breast Cancer in Mice.

The development of functional materials for tumor immunogenicity enhancement is desirable for overcoming the low therapeutic efficiency and easy metastasis during tumor treatments. Herein, the thermoresponsive nanoparticles composed of photothermal agent (PTA) and click reactive reagent are developed for enhanced immunotherapy application. A Ni-bis(dithiolene)-containing PTA with intense near-infrared absorption and efficient photothermal conversion is developed for thermoresponsive nanoparticles construction. The generated heat by encapsulated PTA further induces the phase transition of thermoresponsive nanoparticles with the release of chemotherapy reagent to react with the amino groups on functional proteins, realizing PTT and chemotherapy simultaneously. Moreover, the immunogenic cell death (ICD) of cancer cells evoked by PTT could be further enhanced by the released reactive reagent. As a result, the synergistic effect of photothermal treatment and reaction-mediated chemotherapy can suppress the growth of a primary tumor, and the evoked ICD could further activate the immune response with the suppression of a distant tumor. This synergistic treatment strategy provides a reliable and promising approach for cancer immunotherapy in clinic.

NIR luminogen for low-temperature photothermal therapy by triggering HSP90α down-regulation.

A near-infrared (NIR) luminogen TST was designed and used to efficiently trigger HSP90α protein knockdown through photo-thermal conversion based on a gene interference strategy, by which in vitro and in vivo tumor ablation were significantly acquired at low-temperature.

Photo-Enhanced Chemotherapy Performance in Bladder Cancer Treatment via Albumin Coated AIE Aggregates.

The implementation of cisplatin-based neoadjuvant chemotherapy (NAC) plays a key role in conjunction with surgical resection in preventing bladder cancer progression and recurrence. However, the significant dose-dependent toxic side effects of NAC are still a major challenge. To solve this problem, we developed a photoenhanced cancer chemotherapy (PECC) strategy based on AIEgen ((E)-3-(2-(2-(5-(4-(diphenylamino)phenyl)thiophen-2-yl)vinyl)-1,1-dimethyl-1H-3λ4-benzo[e]indol-3-yl)propane-1-sulfonate), which is abbreviated as BITT. Multifunctional BITT@BSA-DSP nanoparticles (NPs) were employed with an albumin-based nanocarrier decorated with the cisplatin(IV) prodrug and loaded to produce strong near-infrared fluorescence imaging (NIR FLI), and they exhibited good photoenhancement performance via photodynamic therapy (PDT) and photothermal therapy (PTT). In vitro results demonstrated that BITT@BSA-DSP NPs could be efficiently taken up by bladder cancer cells and reduced to release Pt (II) under reductase, ensuring the chemotherapy effect. Furthermore, both in vitro and in vivo evaluation verified that the integration of NIR FL imaging-guided PECC efficiently promoted the sensitivity of bladder cancer to cisplatin chemotherapy with negligible side effects. This work provides a promising strategy to enhance the sensitivity of multiple cancers to chemotherapy drugs and even achieve effective treatments for drug-resistant cancers.

Click Synthesis Enabled Sulfur Atom Strategy for Polymerization-Enhanced and Two-Photon Photosensitization.

Facile tailoring of photosensitizers (PSs) with advanced and synergetic properties is highly expected to broaden and deepen photodynamic therapy (PDT) applications. Herein, a catalyst-free thiol-yne click reaction was employed to develop the sulfur atom-based PSs by using the in situ formed sulfur "heavy atom effect" to enhance the intersystem crossing (ISC), while such an effect can be remarkably magnified by the polymerization. The introduction of a tetraphenylpyrazine-based aggregation-induced emission (AIE) unit was also advantageous in PS design by suppressing their non-radiative decay to facilitate the ISC in the aggregated state. Besides, the resulting sulfur atom electron donor, together with a double-bond π bridge and AIE electron acceptor, created a donor-π-acceptor (D-π-A) molecular system with good two-photon excitation properties. Combined with the high singlet oxygen generation efficiency, the fabricated polymer nanoparticles exhibited an excellent in vitro two-photon-excited PDT towards cancer cells, therefore possessing a huge potential for the deep-tissue disease therapy.

Aggregation-Induced Emission Luminogen-Based Dual-Mode Enzyme-Linked Immunosorbent Assay for Ultrasensitive Detection of Cancer Biomarkers in a Broad Concentration Range.

The enzyme-linked immunosorbent assay (ELISA) is one of the most commonly used methods for measuring antibodies and antigens in biological samples. However, developing new ELISAs with high detection sensitivity and broad detection dynamic ranges without resorting to complicated signal processing and equipment setups remains a challenge. In this work, we report a strategy to simultaneously improve the detection sensitivity and broaden the dynamic range by replacing the chromogenic reagents used in traditional ELISAs with an aggregation-induced emission luminogen (AIEgen). The developed AIE-ELISA could generate complementary absorbance and fluorescence signals with a linear detection range of 1.6-25,000 pg/mL. The application of this dual-mode AIE-ELISA in the detection of the prostate-specific antigen (PSA) realized a limit of detection of 1.3 pg/mL (3.78 × 10-14 M) and dynamic range improvement of approximately 2 orders of magnitude compared to a single-mode ELISA, which enabled it to discriminate a minor PSA difference in a patient's serum. The simpler experimental operation, faster enzyme response speed, and better photostability of AIEgen than the traditional chromogenic reagents used in ELISAs showed that our developed AIE-ELISA holds great potential in the fields of immunoassay, immunohistochemistry, and immunocytochemistry.

A Class of Biocompatible Dye-Protein Complex Optical Nanoprobes.

Molecular organic dyes are classic fluorescent nanoprobes finding tremendous uses in biological and life sciences. Yet, they suffer from low brightness, poor photostability, and lack of functional groups for bioconjugation. Here, we describe a class of biocompatible dye-protein optical nanoprobes, which show long-time photostability, superbrightness, and enriched functional groups. These nanoprobes utilize apoferritin (an intracellular protein for iron stores and release) to encase appropriate molecular organic dyes to produce on-demand fluorescence in aqueous solution. A pH-driven dissociation-reconstitution process of apoferritin subunits allows substantial incorporation of hydrophilic (aggregation caused quenching, ACQ) or hydrophobic (aggregation induced enhancement, AIE) dye molecules into the protein nanocavity (8 nm), producing monodispersed dye-apoferritin nanoparticles (apo-dye-NPs, ∼12 nm). As compared with single dye monomer, single apo-dye-NPs possess hundreds of times larger molar extinction coefficient and 2 orders of magnitude higher absolute luminescence quantum yield (up to 45-fold), multiplying fluorescence brightness up to 2778-fold. We show that varying the type of incorporated dyes entails a precise control over nanoprobe emission profile tunable in a broad spectral range of 370-1300 nm. Mechanical investigations indicate that the diversified microstructures of nanocavity inner surface are able to conform ACQ dyes at reasonable space interval while providing protein-guided-stacking for AIE dyes, thus enhancing fluorescence quantum yield through confining intermolecular quenching and intramolecular rotation. Moreover, apo-dye-NPs are able to emit stable fluorescence (over 13 min) without quenching in confocal imaging of HepG2 cancer cell under ultrahigh laser irradiance (1.3 × 106 W/cm2). These superb properties make them suitable, as demonstrated in this work, for long-term super-resolved structured illumination microscopic cell imaging (spatial resolution, 117 nm) over 48 h, near-infrared (NIR) fluorescence angiography imaging of whole-body blood vessels (spatial resolution, 380 µm), and NIR photoacoustic imaging of liver in vivo.

Augmenting photosynthesis through facile AIEgen-chloroplast conjugation and efficient solar energy utilization.

Photosynthesis is regarded as the foundation for sustaining life on our planet. Light-harvesting is the initial step that activates the subsequent photochemical reactions. In the photosystems, chloroplast is the basic light-driven metabolic factory of higher plant cells. However, there is an incomplete match between the solar radiation spectrum and absorption profile of chloroplasts. It is hard for the photosynthetic pigments to fully utilize the sunlight energy. Here, we designed two new aggregation-induced emission (AIE) molecules with activated alkyl groups (TPE-PPO and TPA-TPO). Via a facile metal-free "Click" reaction, we realized the substantial manipulation of live chloroplasts with the AIE luminogens (AIEgens). Owing to the matched photophysical properties, the AIEgens could harvest harmful ultraviolet radiation (HUVR) and photosynthetically inefficient radiation (PIR), and further convert them into photosynthetically active radiation (PAR) for chloroplast absorption. As a result, the conjugated AIEgen-chloroplast exhibited better capability of water splitting and electron separation. It promoted the generation of adenosine triphosphate (ATP), which is an important product of photosynthesis. This work provides an effective strategy for improving plant photosynthesis.

Synergistic Enhancement of Fluorescence and Magnetic Resonance Signals Assisted by Albumin Aggregate for Dual-Modal Imaging.

Dual-modal fluorescence and magnetic resonance imaging (FLI/MRI) is important for the early diagnosis of malignant tumors. However, facile and opportune strategies to synergistically enhance fluorescence intensity and magnetic resonance (MR) contrast have rarely been reported. Herein, we present a facile strategy using albumin aggregates (AAs) to synergistically enhance the fluorescence intensity by aggregation-induced emission (AIE) and MR contrast with prolonged rotational correlation time (τR) of Gd(III) chelates and the diffusion correlation time (τD) of surrounding water molecules. The amphiphilic dual-modal FLI/MRI probe of NGd was facilely loaded into albumin pockets and then formed AAs to generate a supramolecular structure of NGd-albumin aggregates (NGd-AAs), which show excellent biocompatibility and biosafety, and exhibit superior fluorescence quantum yield and r1 over NGd with 6- and 8-fold enhancement, respectively. Moreover, compared with the clinical MRI contrast agent Gd-DOTA, r1 of NGd-AAs showed a 17-fold enhancement. Therefore, NGd-AAs successfully elicited high-performance dual-modal FLI/MRI in vitro and in vivo and high contrast MR signals were observed in the liver and tumor after intravenous injection of NGd-AAs at a dosage of 6 µmol Gd(III)/kg body weight. This generic and feasible strategy successfully realized a synergistic effect for dual-modal FLI/MRI.

Immunostimulatory AIE Dots for Live-Cell Imaging and Drug Delivery.

The mechanical properties of nanoscale drug carriers play critical roles in regulating nano-bio interactions. For example, the superior deformability of the softer nanoparticles enables them to pass through the biofilters efficiently, facilitating their long blood circulation and better tumor penetration. However, as a novel nanocarrier system, the elimination efficiency of soft nanoparticles from cells is poorly investigated. Here, we report a facile strategy to prepare soft luminescent nanoparticles through self-assembly of amphiphilic aggregation-induced emission (AIE) fluorophores. The prepared soft AIE dots exhibit strong light emission (quantum yield, ∼27.1%) and can reveal the encapsulation and excretion process of NPs in real time. The cell results showed that soft NPs can greatly increase the transfer speed of nanomaterials into cells and accelerate their elimination from cells through the sacrifice of soft AIE dots. We also show that soft AIE dots loaded with cytosine-phosphate-guanine (CpG) oligodeoxynucleotides can induce strong immunostimulatory effects, producing a high level of various proinflammatory cytokines including tumor necrosis factor (TNF)-R, interleukin (IL)-6, and IL-12. This work demonstrates a new design strategy for synthesizing a soft nanocarrier system that can deliver drugs into cells efficiently and then be eliminated from cells quickly.

Conjugated Polymers with Aggregation-Induced Emission Characteristics for Fluorescence Imaging and Photodynamic Therapy.

Accurate diagnosis and treatment have been extensively developed in the field of biomedicine, which put forward higher requirements for the development of biomedical materials with high efficiency and selectivity. Among them, conjugated polymers featuring aggregation-induced emission (AIE) characteristics (AIE conjugated polymers) have stood out in recent years owing to their unique properties, such as intense solid emission, high light-harvesting ability, efficient energy transfer, and high 1 O2 generation ability, which empower them with effective biomedical functions in fluorescence imaging (FLI), photodynamic therapy (PDT), FLI-guided PDT, two-photon excited photodynamic therapy (2PE-PDT), etc. In this review, we highlight recent progress in AIE conjugated polymers and their applications in anticancer and antibacterial areas based on FLI and PDT, and summarize the mechanism of color-tuned fluorescence emission and efficient 1 O2 generation ability. The challenges and perspectives for the future development of AIE conjugated polymers are also discussed.

Site-Selective, Multistep Functionalizations of CO2-Based Hyperbranched Poly(alkynoate)s toward Functional Polymetric Materials.

Hyperbranched polymers constructed from CO2 possess unique architectures and properties; however, they are difficult to prepare. In this work, CO2-based, hyperbranched poly(alkynoate)s (hb-PAs) with high molecular weights and degrees of branching are facilely prepared under atmospheric pressure in only 3 h. Because hb-PAs possess two types of ethynyl groups with different reactivities, they can undergo site-selective, three-step functionalizations with nearly 100% conversion in each step. Taking advantage of this unique feature, functional hb-PAs with versatile properties are constructed that could be selectively tailored to contain hydrophilic oligo(ethylene glycol) chains in their branched chains, on their periphery, or both via tandem polymerizations. Hyperbranched polyprodrug amphiphiles with high drug loading content (44.3 wt%) are also generated, along with an artificial light-harvesting system with high energy transfer efficiency (up to 92%) and white-light-emitting polymers. This work not only provides an efficient pathway to convert CO2 into hyperbranched polymers, but also offers an effective platform for site-selective multistep functionalizations toward functional polymeric materials.

Evoking Photothermy by Capturing Intramolecular Bond Stretching Vibration-Induced Dark-State Energy.

Development of highly effective approaches to desirable photothermal conversion agents is particularly valuable. Herein, we report a concept, namely, bond stretching vibration-induced photothermy, that serves as a mechanism to construct advanced photothermal conversion agents. As a proof-of-concept, two compounds (DCP-TPA and DCP-PTPA) with donor-acceptor (D-A) structures were synthesized. The bond stretching vibration of the pyrazine-containing unit in these molecules is vigorous and insensitive to the external environmental restraint, which efficiently transforms the absorbed photons to dark-state heat energy. The nanoparticles (NPs) of DCP-TPA and DCP-PTPA show rather high photothermal conversion efficiency (52% and 59%) and stronger photoacoustic (PA) signal than commercial methylene blue and reported high-performance semiconducting polymer nanoparticles. The DCP-PTPA NPs perform better than DCP-TPA NPs in terms of photothermal conversion, PA signal production, and in vivo PA tumor imaging because of the increased bond stretching vibration in the former molecule.

Selective viable cell discrimination by a conjugated polymer featuring aggregation-induced emission characteristic.

Detection and discrimination viable cells with high selectivity are critically important in monitoring cell activity to provide key information on therapeutic efficacy. In this work, a tetraphenylethene-based conjugated polymer featuring aggregation-induced emission (AIE) characteristic was designed and synthesized, which could be used to selectively discriminate viable cells from apoptotical cells, dead cells and pathogens. Thanks to its synergistic effect and high molecular weight, the polymer shows unique advantages over low-mass organic probes, such as better biocompatibility, higher selectivity and stronger tracing ability. Moreover, we figured out that the negatively charged side-chain of the conjugated polymer and the endocytosis process both play crucial roles in this selective discrimination behavior, making this probe a powerful tool for guiding precise cancer therapy.

Utilizing a Pyrazine-Containing Aggregation-Induced Emission Luminogen as an Efficient Photosensitizer for Imaging-Guided Two-Photon Photodynamic Therapy.

The development of novel photosensitizers with aggregation-induced emission (AIE) characteristics has aroused tremendous interest, because it could combine efficient bioimaging with precise photodynamic therapy, which would thus dramatically promote applications in biomedical treatment. Among various AIE luminogens (AIEgens), heterocycle-containing molecules are highly promising for this usage because of their high photostability and tunable electronic properties. In this work, a pyrazine-containing AIEgen with a dicyanopyrazine moiety as an electron acceptor and a triphenylamine unit as an electron donor was chosen for study. The V-shaped donor-π-acceptor-π-donor structure of the AIEgen endowed its nanoparticles with excellent nonlinear optical properties for two-photon cell imaging under near-infrared laser excitation. Also, under the same excitation, the nanoparticles could produce reactive oxygen species and further kill the cells efficiently and accurately. The present work thus presents a pyrazine-containing AIEgen as a new photosensitizer for imaging-guided two-photon photodynamic therapy and gives more opportunities for deep-tissue treatment of cancer in future research.

Phenol-yne Click Polymerization: An Efficient Technique to Facilely Access Regio- and Stereoregular Poly(vinylene ether ketone)s.

Alkyne-based click polymerizations have been well-established. However, in order to expand the family to synthesize polymers with new structures and novel properties, new types of click polymerizations are highly demanded. In this study, for the first time, we established a new efficient and powerful phenol-yne click polymerization. The activated diynes and diphenols could be facilely polymerized in the presence of the Lewis base catalyst of 4-dimethylaminopyridine (DMAP) under mild reaction conditions. Regio- and stereoregular poly(vinylene ether ketone)s (PVEKs) with high molecular weights (up to 35 200) were obtained in excellent yields (up to 99.0 %). The reaction mechanism was well explained under the assistance of density functional theory (DFT) calculation. Furthermore, since the vinyl ether sequence acts as a stable but acid-liable linkage, the polymers could be decomposed under acid conditions, rendering them applicable in biomedical and environmental fields.

Metal-Free Multicomponent Tandem Polymerizations of Alkynes, Amines, and Formaldehyde toward Structure- and Sequence-Controlled Luminescent Polyheterocycles.

Sequence-controlled polymers, including biopolymers such as DNA, RNA, and proteins, have attracted much attention recently because of their sequence-dependent functionalities. The development of an efficient synthetic approach for non-natural sequence-controlled polymers is hence of great importance. Multicomponent polymerizations (MCPs) as a powerful and popular synthetic approach for functional polymers with great structural diversity have been demonstrated to be a promising tool for the synthesis of sequence-controlled polymers. In this work, we developed a facile metal-free one-pot multicomponent tandem polymerization (MCTP) of activated internal alkynes, aromatic diamines, and formaldehyde to successfully synthesize structural-regulated and sequence-controlled polyheterocycles with high molecular weights (up to 69 800 g/mol) in high yields (up to 99%). Through such MCTP, polymers with the in situ generated multisubstituted tetrahydropyrimidines or dihydropyrrolones in the backbone and inherent luminescence can be easily obtained with high atom economy and environmental benefit, which is inaccessible by other synthetic approaches.

A macrocyclic 1,4-bis(4-pyridylethynyl)benzene showing unique aggregation-induced emission properties.

A box-like macrocycle based on 1,4-bis(4-pyridylethynyl)benzene was derived in high yield. The macrocyclic fluorogen shows unique aggregation-induced emission properties.

Long-Term Tracking of the Osteogenic Differentiation of Mouse BMSCs by Aggregation-Induced Emission Nanoparticles.

Bone marrow-derived mesenchymal stem cells (BMSCs) have shown great potential for bone repair due to their strong proliferation ability and osteogenic capacity. To evaluate and improve the stem cell-based therapy, long-term tracking of stem cell differentiation into bone-forming osteoblasts is required. However, conventional fluorescent trackers such as fluorescent proteins, quantum dots, and fluorophores with aggregation-caused quenching (ACQ) characteristics have intrinsic limitations of possible interference with stem cell differentiation, heavy metal cytotoxicity, and self-quenching at a high labeling intensity. Herein, we developed aggregation-induced emission nanoparticles decorated with the Tat peptide (AIE-Tat NPs) for long-term tracking of the osteogenic differentiation of mouse BMSCs without interference of cell viability and differentiation ability. Compared with the ability of the commercial Qtracker 655 for tracking of only 6 passages of mouse BMSCs, AIE-Tat NPs have shown a much superior performance in long-term tracking for over 12 passages. Moreover, long-term tracking of the osteogenic differentiation process of mouse BMSCs was successfully conducted on the biocompatible hydroxyapatite scaffold, which is widely used in bone tissue engineering. Thus, AIE-Tat NPs have promising applications in tracking stem cell fate for bone repair.