Highly Efficient Photosensitizers with Far-Red/Near-Infrared Aggregation-Induced Emission for In Vitro and In Vivo Cancer Theranostics

Aggregate Science: From Structures to Properties

Molecular science entails the study of structures and properties of materials at the level of single molecules or small interacting complexes of molecules. Moving beyond single molecules and well-defined complexes, aggregates (i.e., irregular clusters of many molecules) serve as a particularly useful form of materials that often display modified or wholly new properties compared to their molecular components. Some unique structures and phenomena such as polymorphic aggregates, aggregation-induced symmetry breaking, and cluster excitons are only identified in aggregates, as a few examples of their exotic features. Here, by virtue of the flourishing research on aggregation-induced emission, the concept of "aggregate science" is put forward to fill the gaps between molecules and aggregates. Structures and properties on the aggregate scale are also systematically summarized. The structure-property relationships established for aggregates are expected to contribute to new materials and technological development. Ultimately, aggregate science may become an interdisciplinary research field and serves as a general platform for academic research.

An All-Round Athlete on the Track of Phototheranostics: Subtly Regulating the Balance between Radiative and Nonradiative Decays for Multimodal Imaging-Guided Synergistic Therapy

Aiming to achieve versatile phototheranostics with the integrated functionalities of multiple diagnostic imaging and synergistic therapy, the optimum use of dissipated energy through both radiative and nonradiative pathways is definitely appealing, yet a significantly challenging task. To the best of the knowledge, there have been no previous reports on a single molecular species effective at affording all phototheranostic modalities including fluorescence imaging (FLI), photoacoustic imaging (PAI), photothermal imaging (PTI), photodynamic therapy (PDT), and photothermal therapy (PTT). Herein, a simple and highly powerful one-for-all phototheranostics based on aggregation-induced emission (AIE)-active fluorophores is tactfully designed and constructed. Thanks to its strong electron donor-acceptor interaction and finely modulated intramolecular motion, the AIE fluorophore-based nanoparticles simultaneously exhibit bright near-infrared II (NIR-II) fluorescence emission, efficient reactive oxygen species generation, and high photothermal conversion efficiency upon NIR irradiation, indicating the actualization of a balance between radiative and nonradiative energy dissipations. Furthermore, the unprecedented performance on NIR-II FLI-PAI-PTI trimodal-imaging-guided PDT-PTT synergistic therapy is demonstrated by the precise tumor diagnosis and complete tumor elimination outcomes. This study thus brings a new insight into the development of superior versatile phototheranostics for practical cancer theranostics.

Aggregation-Induced Emission Luminogens Married to 2D Black Phosphorus Nanosheets for Highly Efficient Multimodal Theranostics

Inspired by the respective advantages of aggregation-induced emission (AIE)-active photosensitizers and black phosphorus nanomaterials in cancer treatment, the facile construction of novel AIE photosensitizers married to 2D black phosphorus nanosheets and their application for multimodal theranostics are demonstrated. The developed nanomaterial simultaneously possesses distinctive properties and multiple functions including excellent stability, good biocompatibility, intensive fluorescence emission in the NIR region, high-performance reactive oxygen species generation, good photothermal conversion efficiency, outstanding cellular uptake, and effective accumulation at the tumor site. Both in vitro and in vivo evaluation show that the presented nanotheranostic system is an excellent candidate for NIR fluorescence-photothermal dual imaging-guided synergistic photodynamic-photothermal therapies. This study thus not only extends the applications scope of AIE and black phosphorus materials, but also offers useful insights into designing a new generation of cancer theranostic protocol for potential clinical applications.

Stable Organic Photosensitizer Nanoparticles with Absorption Peak beyond 800 Nanometers and High Reactive Oxygen Species Yield for Multimodality Phototheranostics

Effective multimodality phototheranostics under deep-penetration laser excitation is highly desired for tumor medicine, which is still at a deadlock due to lack of versatile photosensitizers with absorption located in the long-wavelength region. Herein, we demonstrate a stable organic photosensitizer nanoparticle based on molecular engineering of benzo[c]thiophene (BT)-based photoactivated molecules with strong wavelength-tunable absorption in the near-infrared region. Via molecular design, the absorption and singlet oxygen generation of BT molecules would be reliably tuned. Importantly, the nanoparticles with a red-shifted absorption peak of 843 nm not only show over 10-fold reactive oxygen species yield compared with indocyanine green but also demonstrate a notable photothermal effect and photoacoustic signal upon 808 nm excitation. The in vitro and in vivo experiments substantiate good multimodal anticancer efficacy and imaging performance of BT theranostics. This work provides an organic photosensitizer nanoparticle with long-wavelength excitation and high photoenergy conversion efficiency for multimodality phototherapy.

Targeted Theranostics for Tuberculosis: A Rifampicin-Loaded Aggregation-Induced Emission Carrier for Granulomas Tracking and Anti-Infection

Tuberculosis (TB) causes a global burden with its high rates of infection and death, especially the irrepressible threats of latent infection and drug resistance. Therefore, it is important to construct efficient theranostics for the prevention and control of TB. Herein, we created a targeted theranostic strategy for TB with a rifampicin-loaded aggregation-induced emission (AIE) carrier and performed testing in laboratory animals. The AIE carrier was constructed to localize in the granulomas and emit fluorescent signals at the early stage of infection, enabling the early diagnosis of TB. Subsequently, reactive oxygen species (ROS) were generated to eradicate infection, and the loaded rifampicin (RIF) was released for the synergistic treatment of persistent bacteria. Furthermore, targeted TB therapy was performed with the light-controlled release of ROS and accurate delivery of RIF, which realizes an anti-infection effect, providing an especially important treatment for drug-resistant TB. Thus, targeted theranostics for TB in laboratory animals possess the potential to become granulomas-tracking and anti-infection strategies for the diagnosis and treatment of TB.

The Secret Lives of Fluorescent Membrane Probes as Revealed by Molecular Dynamics Simulations

Fluorescent probes have been employed for more than half a century to study the structure and dynamics of model and biological membranes, using spectroscopic and/or microscopic experimental approaches. While their utilization has led to tremendous progress in our knowledge of membrane biophysics and physiology, in some respects the behavior of bilayer-inserted membrane probes has long remained inscrutable. The location, orientation and interaction of fluorophores with lipid and/or water molecules are often not well known, and they are crucial for understanding what the probe is actually reporting. Moreover, because the probe is an extraneous inclusion, it may perturb the properties of the host membrane system, altering the very properties it is supposed to measure. For these reasons, the need for independent methodologies to assess the behavior of bilayer-inserted fluorescence probes has been recognized for a long time. Because of recent improvements in computational tools, molecular dynamics (MD) simulations have become a popular means of obtaining this important information. The present review addresses MD studies of all major classes of fluorescent membrane probes, focusing in the period between 2011 and 2020, during which such work has undergone a dramatic surge in both the number of studies and the variety of probes and properties accessed.

Rhodanine-based Knoevenagel reaction and ring-opening polymerization for efficiently constructing multicyclic polymers

Cyclic polymers have a number of unique physical properties compared with those of their linear counterparts. However, the methods for the synthesis of cyclic polymers are very limited, and some multicyclic polymers are still not accessible now. Here, we found that the five-membered cyclic structure and electron withdrawing groups make methylene in rhodanine highly active to aldehyde via highly efficient Knoevenagel reaction. Also, rhodanine can act as an initiator for anionic ring-opening polymerization of thiirane to produce cyclic polythioethers. Therefore, rhodanine can serve as both an initiator for ring-opening polymerization and a monomer in Knoevenagel polymerization. Via rhodanine-based Knoevenagel reaction, we can easily incorporate rhodanine moieties in the backbone, side chain, branched chain, etc, and correspondingly could produce cyclic structures in the backbone, side chain, branched chain, etc, via rhodanine-based anionic ring-opening polymerization. This rhodanine chemistry would provide easy access to a wide variety of complex multicyclic polymers.

Tuning molecular aggregation to achieve highly bright AIE dots for NIR-II fluorescence imaging and NIR-I photoacoustic imaging

Currently, bright aggregation-induced emission luminogens (AIEgens) with high photoluminescence quantum yields (PLQYs) in the NIR-II region are still limited, and thus an efficient strategy to enhance NIR-II fluorescence performance through tuning molecular aggregation is proposed here. The synthesized donor-acceptor tailored AIEgen (DTPA-TBZ) not only exhibits an excellent absorptivity in the NIR-I region, but also good fluorescence signals in the NIR-II region with an emission extending to 1200 nm. Benefiting from such improved intramolecular restriction and aggregation, a significant absolute PLQY value of 8.98% was obtained in solid DTPA-TBZ. Encouragingly, the resulting AIE dots also exhibit a high relative PLQY of up to 11.1% with IR 26 as the reference (PLQY = 0.5%). Finally, the AIE dots were applied in high performance NIR-II fluorescence imaging and NIR-I photoacoustic (PA) imaging: visualization of abdominal vessels, hind limb vasculature, and cerebral vessels with high signal to background ratios was performed via NIR-II imaging; Moreover, PA imaging has also been performed to clearly observe tumors in vivo. These results demonstrate that by finely tuning molecular aggregation in DTPA-TBZ, a good NIR-I absorptivity and a highly emissive fluorescence in the NIR-II region can be achieved simultaneously, finally resulting in a promising dual-modal imaging platform for real-world applications to achieve precise cancer diagnostics.

Facile Synthesis of Efficient Luminogens with AIE Features for Three-Photon Fluorescence Imaging of the Brain through the Intact Skull

Visualization of the brain in its native environment is important for understanding common brain diseases. Herein, bright luminogens with remarkable aggregation-induced emission (AIE) characteristics and high quantum yields of up to 42.6% in the solid state are synthesized through facile reaction routes. The synthesized molecule, namely BTF, shows ultrabright far-red/near-infrared emission and can be fabricated into AIE dots by a simple nanoprecipitation procedure. Due to their high brightness, large Stokes shift, good biocompatibility, satisfactory photostability, and large three-photon absorption cross section, the AIE dots can be utilized as efficient fluorescent nanoprobes for in vivo brain vascular imaging through the intact skull by a three-photon fluorescence microscopy imaging technique. This is the first example of using AIE dots for the visualization of the cerebral stroke process through the intact skull of a mouse with high penetration depth and good image contrast. Such good results are anticipated to open up a new venue in the development of efficient emitters with strong nonlinear optical effects for noninvasive bioimaging of living brain.

Aggregation-Induced Emission: New Vistas at the Aggregate Level

Aggregation-induced emission (AIE) describes a photophysical phenomenon in which molecular aggregates exhibit stronger emission than the single molecules. Over the course of the last 20 years, AIE research has made great strides in material development, mechanistic study and high-tech applications. The achievements of AIE research demonstrate that molecular aggregates show many properties and functions that are absent in molecular species. In this review, we summarize the advances in the field of AIE and its related areas. We specifically focus on the new properties of materials attained by molecular aggregates beyond the microscopic molecular level. We hope this review will inspire more research into molecular ensembles at and beyond the meso level and lead to the significant progress in material and biological science.

Efficient photosensitizers with aggregation-induced emission characteristics for lysosome- and Gram-positive bacteria-targeted photodynamic therapy

Two efficient photosensitizers (PSs) with aggregation-induced emission characteristics were designed and synthesized for specific lysosome-targeted photodynamic therapy (PDT). Both PSs efficiently discriminated Gram-positive bacteria from Gram-negative bacteria and killed Gram-positive bacteria through the PDT effect.

Iridium(III) Complex-Derived Polymeric Micelles with Low Dark Toxicity and Strong NIR Excitation for Phototherapy and Chemotherapy

Iridium(III) complexes are potent candidates for photodynamic therapy. However, their clinical usage is impeded by their poor water solubility, high dark toxicity, and negligible absorption in near-infrared region (NIR region). Here, it is proposed to solve these challenges by developing an iridium(III) complexe-based polymeric micelle system. This system is self-assembled using an iridium(III) complex-containing amphiphilic block polymer. The upconversion nanoparticles are included in the polymeric micelles to permit NIR excitation. Compared with the nonformulated iridium(III) complexes, under NIR stimulation, this polymeric micelle system exhibits higher ¹ O₂ generation efficiency, negligible dark toxicity, excellent tumor-targeting ability, and synergistic phototherapy-chemotherapy effect both in vitro and in vivo.

Molecular Design of Highly Efficient Heavy-Atom-Free Triplet BODIPY Derivatives for Photodynamic Therapy and Bioimaging

Novel BODIPY photosensitizers were developed for imaging-guided photodynamic therapy. The introduction of a strong electron donor to the BODIPY core through a phenyl linker combined with the twisted arrangement between the donor and the BODIPY acceptor is essential for reducing the energy gap between the lowest singlet excited state and the lowest triplet state (ΔE_ST ), leading to a significant enhancement in the intersystem crossing (ISC) of the BODIPYs. Remarkably, the BDP-5 with the smallest ΔE_ST (ca. 0.44 eV) exhibited excellent singlet oxygen generation capabilities in both organic and aqueous solutions. BDP-5 also displayed bright emission in the far-red/near-infrared region in the condensed states. More importantly, both in vitro and in vivo studies demonstrated that BDP-5 NPs displayed a high potential for photodynamic cancer therapy and bioimaging.

High-Performance Quinoline-Malononitrile Core as a Building Block for the Diversity-Oriented Synthesis of AIEgens

In vivo fluorescent monitoring of physiological processes with high-fidelity is essential in disease diagnosis and biological research, but faces extreme challenges due to aggregation-caused quenching (ACQ) and short-wavelength fluorescence. The development of high-performance and long-wavelength aggregation-induced emission (AIE) fluorophores is in high demand for precise optical bioimaging. The chromophore quinoline-malononitrile (QM) has recently emerged as a new class of AIE building block that possesses several notable features, such as red to near-infrared (NIR) emission, high brightness, marked photostability, and good biocompatibility. In this minireview, we summarize some recent advances of our established AIE building block of QM, focusing on the AIE mechanism, regulation of emission wavelength and morphology, the facile scale-up and fast preparation for AIE nanoparticles, as well as potential biomedical imaging applications.

Supramolecular materials based on AIE luminogens (AIEgens): construction and applications

The emergence of aggregation-induced emission luminogens (AIEgens) has significantly stimulated the development of luminescent supramolecular materials because their strong emissions in the aggregated state have resolved the notorious obstacle of the aggregation-caused quenching (ACQ) effect, thereby enabling AIEgen-based supramolecular materials to have a promising prospect in the fields of luminescent materials, sensors, bioimaging, drug delivery, and theranostics. Moreover, in contrast to conventional fluorescent molecules, the configuration of AIEgens is highly twisted in space. Investigating AIEgens and the corresponding supramolecular materials provides fundamental insights into the self-assembly of nonplanar molecules, drastically expands the building blocks of supramolecular materials, and pushes forward the frontiers of supramolecular chemistry. In this review, we will summarize the basic concepts, seminal studies, recent trends, and perspectives in the construction and applications of AIEgen-based supramolecular materials with the hope to inspire more interest and additional ideas from researchers and further advance the development of supramolecular chemistry.

Aggregation-Induced Emission Photosensitizers: From Molecular Design to Photodynamic Therapy

Photodynamic therapy (PDT) has emerged as a promising noninvasive treatment option for cancers and other diseases. The key factor that determines the effectiveness of PDT is the photosensitizers (PSs). Upon light irradiation, the PSs would be activated, produce reactive oxygen species (ROS), and induce cell death. One of the challenges is that traditional PSs adopt a large flat disc-like structure, which tend to interact with the adjacent molecules through strong π-π stacking that reduces their ROS generation ability. Aggregation-induced emission (AIE) molecules with a twisted configuration to suppress strong intermolecular interactions represent a new class of PSs for image-guided PDT. In this Miniperspective, we summarize the recent progress on the design rationale of AIE-PSs and the strategies to achieve desirable theranostic applications in cancers. Subsequently, approaches of combining AIE-PS with other imaging and treatment modalities, challenges, and future directions are addressed.

Bright red aggregation-induced emission nanoparticles for multifunctional applications in cancer therapy

Developing multifunctional photosensitizers (PSs) is needed to effectively simplify cancer treatment, but it remains a big challenge. Here, two red-emitting AIE-active, donor-acceptor (D-A) PSs with small ΔE ST and their AIE nanoparticles, are rationally designed and synthesized. The PS1 NPs exhibit bright red-emission with high quantum yield, appropriate 1O2 generation ability and good biocompatibility. More importantly, PS1 NPs can strongly light up the cytoplasm by gently shaking the cells for only 5 s at room temperature, indicating ultrafast staining and mild incubation conditions. In vitro and in vivo cell tracing demonstrate that PS1 NPs can track cells over 14 days, and effectively inhibit tumor growth upon irradiation. To the best of our knowledge, this work is the first example of a PS that integrates image-guided PDT, ultrafast staining and long-term tracing functions, demonstrating the "all-in-one" concept which offers great advantages for potential clinical applications.

AIE nanodots scaffolded by mini-ferritin protein for cellular imaging and photodynamic therapy

Photodynamic therapy (PDT) is one of the most elegant cancer treatment strategies that can be controlled by a beam of light with non-invasion, precise control, and high spatiotemporal accuracy. An ideal photosensitizer (PS) is the key to ensure the efficacy of PDT. Due to their hydrophobic and rigid planar structures, most traditional PSs are prone to aggregate under physiological conditions, which causes fluorescence quenching and significantly reduces reactive oxygen species (ROS) generation. Fortunately, the emergence of aggregation-induced emission (AIE) dyes offers a potential opportunity to overcome these limitations. When AIE PS molecules are in the aggregation state, the fluorescence intensity and ROS production can be increased. We herein use red AIE PS molecules to prepare stable AIE nanodots for cell imaging and PDT via a simple method with a highly negatively charged mini-ferritin protein as the scaffold. The as-prepared protein-AIE nanodots show strong fluorescence emission and efficient singlet oxygen generation, with good stability, relatively long wavelengths of absorption and emission, and negligible dark toxicity. The mini-ferritin-AIE system may be useful in developing novel functional probes for tumour nanotheranostics.

Highly efficient singlet oxygen generation, two-photon photodynamic therapy and melanoma ablation by rationally designed mitochondria-specific near-infrared AIEgens

Photosensitizers (PSs) with multiple characteristics, including efficient singlet oxygen (¹O₂) generation, cancer cell-selective accumulation and subsequent mitochondrial localization as well as near-infrared (NIR) excitation and bright NIR emission, are promising candidates for imaging-guided photodynamic therapy (PDT) but rarely concerned. Herein, a simple rational strategy, namely modulation of donor-acceptor (D-A) strength, for molecular engineering of mitochondria-targeting aggregation-induced emission (AIE) PSs with desirable characteristics including highly improved ¹O₂ generation efficiency, NIR emission (736 nm), high specificity to mitochondria, good biocompatibility, high brightness and superior photostability is demonstrated. Impressively, upon light irradiation, the optimal NIR AIE PS (DCQu) can generate ¹O₂ with efficiency much higher than those of commercially available PSs. The excellent two-photon absorption properties of DCQu allow two-photon fluorescence imaging of mitochondria and subsequent two-photon excited PDT. DCQu can selectively differentiate cancer cells from normal cells without the aid of extra targeting ligands. Upon ultralow-power light irradiation at 4.2 mW cm^-2, in situ mitochondrial photodynamic activation to specifically damage cancer cells and efficient in vivo melanoma ablation are demonstrated, suggesting superior potency of the AIE PS in imaging-guided PDT with minimal side effects, which is promising for future precision medicine.

Cooperation therapy between anti-growth by photodynamic-AIEgens and anti-metastasis by small molecule inhibitors in ovarian cancer

Metastasis is one of the main causes of death and treatment failure in ovarian cancer. Some small molecule inhibitors can effectively inhibit the metastasis of primary tumors. However, they do not kill the primary tumor cells, which may lead to continuous proliferation. Herein, we have prepared a multifunctional nanoparticles named TPD@TB/KBU2046, which consisted of three functional moieties: (1) KBU2046 (small molecule inhibitor) that can inhibit the metastasis of the primary tumors, (2) TB (photodynamic-AIEgens) that may suppress the growth of the primary tumors, and (3) TPD, which contains TMTP1 (a targeting peptide, which specifically binds to highly metastatic tumor cells) that can enhance the TB/KBU2046 dosage in the tumor site. Methods: The TPD@TB/KBU2046 was prepared by nano-precipitation method. We linked the targeting peptide (TMTP1) to the nanoparticles via amidation reaction. TPD@TB/KBU2046 nanoparticles were characterized for encapsulation efficiency, particle size, absorption spectra, emission spectra and ROS production. The combinational efficacy in image-guided anti-metastasis and photodynamic therapy of TPD@TB/KBU2046 was explored both in vitro and in vivo. Results: The TPD@TB/KBU2046 showed an average hydrodynamic size of approximately 50 nm with good stability. In vitro, TPD@TB/KBU2046 not only inhibited the metastasis of the tumors, but also suppressed the growth of the tumors under AIEgens-mediated photodynamic therapy. In vivo, we confirmed that TPD@TB/KBU2046 has the therapeutic effects of anti-tumor growth and anti-metastasis through subcutaneous and orthotopic ovarian tumor models. Conclusion: Our findings provided an effective strategy to compensate for the congenital defects of some small molecule inhibitors and thus enhanced the therapeutic efficacy of ovarian cancer.

An aggregation-induced emission dye-powered afterglow luminogen for tumor imaging

Semiconducting polymer (SP)-based afterglow luminogens are showing increasing potential for in vivo imaging because of their long-life luminescence and the associated benefits (e.g., zero-autofluorescence background and high signal-to-noise ratio). However, such organic afterglow luminescence agents are still rare and their application is usually limited by their relatively low afterglow intensity and short afterglow duration. Herein, we report an aggregation-induced emission (AIE) dye-powered SP afterglow luminogen by leveraging on the unique characteristics of an AIE dye to circumvent the concentration-quenching effect, enhance afterglow intensity and prolong afterglow duration. The underlying working mechanism is investigated by a series of experiments and it is found that the AIE dye provides sufficient 1O2 to excite SPs and form massive amounts of high-energy intermediates, and then the SP intermediates emit photons that can activate the AIE dye to generate 1O2 and simultaneously trigger the energy transfer process between the SPs and AIE dye, resulting in a deep-red emission. It is this closed-loop of "photon-1O2-SP intermediates-photon" that provides the afterglow emission even after the cessation of the excitation light. The as-prepared luminogen shows good performance in in vivo tumour imaging. This study demonstrates the advantages of AIE-facilitated afterglow luminescence and discloses its mechanism, and hopefully it could inspire the development of other innovative designs for cancer theranostics.

Mitochondria-targeted aggregation-induced emission active near infrared fluorescent probe for real-time imaging

Mitochondria are essential organelles in eukaryotic cells and act as the energy powerhouse and biosynthetic compartment. Fluorescent dyes are widely used powerful molecular tools for analytical sensing and optical imaging. Low photostability, short excitation and emission wavelengths, and aggregation-induced quenching effects restrict the application of traditional commercial mitochondrial fluorescent probes for bioimaging. In this study, using rhodamine as the acceptor and phenothiazine as the donor, we synthesized a novel mitochondrial-targeted near infrared (NIR) fluorescent probe, MIT-PZR. Due to low cytotoxicity, great photostability and high specificity for mitochondria targeting, MIT-PZR has enormous potential for cell imaging. Furthermore, with a sizeable Stokes shift (emission peak at 705 nm), MIT-PZR penetrated tissues providing stable red fluorescence for imaging in vivo. The histological assessment of various tissues after treatment with MIT-PZR indicated that it has good biocompatibility. Thus, MIT-PZR is a promising mitochondrial NIR fluorescent probe for future application in clinical diagnosis and modern biological research.

Chlorination vs. fluorination: a study of halogenated benzo[c][1,2,5]thiadiazole-based organic semiconducting dots for near-infrared cellular imaging

The chlorinated dots based on chlorinated benzo[c][1,2,5]thiadiazole unit possess higher fluorescence quantum yields, larger Stokes shifts, and better photostability than the fluorinated dots.

Mitochondria-anchoring and AIE-active photosensitizer for self-monitored cholangiocarcinoma therapy

An AIE-active photosensitizer, TTVPHE, can fast penetrate into cancer cells and efficiently trigger mitochondria-dependent apoptotic pathway with self-monitoring ability.

Near-infrared-emitting AIE multinuclear cationic Ir(iii) complex-assembled nanoparticles for photodynamic therapy

The first pure NIR-emitting AIE multinuclear Ir(iii) complex NPs obtained by self-assembly exhibit excellent cell imaging and PDT performance.

The construction of an AIE-based controllable singlet oxygen generation system directed by a supramolecular strategy

An aggregation-induced emission based controllable singlet oxygen generation system has been successfully fabricated in an aqueous phase based on supramolecular host–guest assembly.

Pyridinium-substituted tetraphenylethylene salt-based photosensitizers by varying counter anions: a highly efficient photodynamic therapy for cancer cell ablation and bacterial inactivation

A highly efficient photodynamic therapy of cancer cell ablation and bacterial inactivation by two AIEgens was reported.

A two-photon AIE fluorophore as a photosensitizer for highly efficient mitochondria-targeted photodynamic therapy

Nowadays, photodynamic therapy (PDT) has become an effective method for cancer therapy.

The butterfly effect in bisfluorenylidene-based dihydroacenes: aggregation induced emission and spin switching

Linear acenes are a well-studied class of polycyclic aromatic hydrocarbons and their established physical properties have led to their widespread application across the field of organic electronics. However, their quinoidal forms - dihydroacenes - are much less explored and exhibit vastly different photophysical and electronic properties due to their non-planar, cross-conjugated nature. In this work, we present a series of difluorenylidene dihydroacenes which exhibit a butterfly-like structure with a quinoidal skeleton, resulting in comparatively higher optical gaps and lower redox activities than those of their planar analogs. We found that these compounds exhibit aggregation induced emission (AIE), activated through restriction of the "flapping" vibrational mode of the molecules in the solid state. Furthermore, anthracene-containing dihydroacenes exhibit thermally activated ground-state spin switching as evidenced by planarization of the acene core and diradical activity recorded by EPR. These two characteristics in this relatively unexplored class of materials provide new insights for the design of multifunctional materials.

Manipulating exciton dynamics of thermally activated delayed fluorescence materials for tuning two-photon nanotheranostics

Rational manipulation of energy utilization from excited-state radiation of theranostic agents with a donor–acceptor structure is relatively unexplored. Herein, we present an effective strategy to tune the exciton dynamics of radiative excited state decay for augmenting two-photon nanotheranostics. As a proof of concept, two thermally activated delayed fluorescence (TADF) molecules with different electron-donating segments are engineered, which possess donor–acceptor structures and strong emissions in the deep-red region with aggregation-induced emission characteristics. Molecular simulations demonstrate that change of the electron-donating sections could effectively regulate the singlet–triplet energy gap and oscillator strength, which promises efficient energy flow. A two-photon laser with great permeability is used to excite TADF NPs to perform as theranostic agents with singlet oxygen generation and fluorescence imaging. These unique performances enable the proposed TADF emitters to exhibit tailored balances between two-photon singlet oxygen generation and fluorescence emission. This result demonstrates that TADF emitters can be rationally designed as superior candidates for nanotheranostic agents by the custom controlling exciton dynamics.

Exciton dynamics can be manipulated rationally in the design of TADF materials for nanotheranostics. Regulating the ΔE_ST and f promises efficient energy flow for tailoring balances between singlet oxygen generation and fluorescence emission.

Intrinsically Cancer-Mitochondria-Targeted Thermally Activated Delayed Fluorescence Nanoparticles for Two-Photon-Activated Fluorescence Imaging and Photodynamic Therapy

A recent breakthrough in the discovery of thermally activated delayed fluorescence (TADF) emitters characterized by small single-triplet energy offsets (ΔE_ST) offers a wealth of new opportunities to exploit high-performance metal-free photosensitizers. In this report, two intrinsically cancer-mitochondria-targeted TADF emitters-based nanoparticles (TADF NPs) have been developed for two-photon-activated photodynamic therapy (PDT) and fluorescence imaging. The as-prepared TADF NPs integrate the merits of (1) high ¹O₂ quantum yield of 52%, (2) sufficient near-infrared light penetration depth due to two-photon activation, and (3) excellent structure-inherent mitochondria-targeting capabilities without extra chemical or physical modifications, inducing remarkable endogenous mitochondria-specific reactive oxygen species production and excellent cancer-cell-killing ability at an ultralow light irradiance. We believe that the development of such intrinsically multifunctional TADF NPs stemming from a single molecule will provide new insights into exploration of novel PDT agents with strong photosensitizing ability for various biomedical applications.

Evaluation of Structure-Function Relationships of Aggregation-Induced Emission Luminogens for Simultaneous Dual Applications of Specific Discrimination and Efficient Photodynamic Killing of Gram-Positive Bacteria

Bacterial infectious diseases, especially those caused by Gram-positive bacteria, have been seriously threatening human health. Preparation of a multifunctional system bearing both rapid bacterial differentiation and effective antibacterial effects is highly in demand, but remains a severe challenge. Herein, we rationally designed and successfully developed a sequence of aggregation-induced emission luminogens (AIEgens) with orderly enhanced D-A strength. Evaluation of structure-function relationships reveals that AIEgens having intrinsic positive charge and proper ClogP value are able to stain Gram-positive bacteria. Meanwhile, one of the presented AIEgens (TTPy) can generate reactive oxygen species (ROS) in extraordinarily high efficiency under white light irradiation due to the smaller singlet-triplet energy gap. Thanks to the NIR emission, excellent specificity to Gram-positive bacteria, and effective ROS generation efficiency, TTPy has been proved to perform well in selective photodynamic killing of Gram-positive bacteria in vitro, such as S. aureus and S. epidermidis, even in S. aureus-infected rat wounds.

Two-photon AIE luminogen labeled multifunctional polymeric micelles for theranostics

Intelligent polymeric micelles with fluorescence imaging feature have been emerged as promising tools for theranostics. However, conventional fluorescent dyes are limited by short wavelength excitation, interference of tissue autofluorescence, limited imaging depth and quenched emission in aggregation state. Methods: We synthesized a novel mPEG-SS-Poly (AEMA-co-TBIS) (mPEATss) copolymer to develop multifunctional polymeric micelles with great AIE feature for cancer therapy and AIE active two-photon bioimaging. The stimuli-responsive behavior and AIE active two-photon cell and tissue imaging as well as in vitro and in vivo antitumor ability of DOX-loaded mPEATss were studied. Results: mPEATss micelles showed excellent AIE active two-photon cell imaging ability and deep tissue imaging ability. Antitumor drug DOX could be encapsulated to form a drug-loaded micellar system with a small diameter of 65 nm. The disassembly and charge-conversion of mPEATss micelles could be triggered by acidic environment, resulting in accelerated drug release and great antitumor efficacy. In vivo, ex vivo imaging and in vivo pharmacokinetic study demonstrated that mPEATss micelles could efficiently accumulate in tumor sites, which ensured ideal anticancer effect. Conclusions: This pH and redox dual responsive and AIE active two-photon imaging polymeric micelles would be a promising candidate for theranostics.

Red/Near-Infrared Thermally Activated Delayed Fluorescence OLEDs with Near 100 % Internal Quantum Efficiency

Developing red thermally activated delayed fluorescence (TADF) emitters, attainable for both high-efficient red organic light-emitting diodes (OLEDs) and non-doped deep red/near-infrared (NIR) OLEDs, is challenging. Now, two red emitters, BPPZ-PXZ and mDPBPZ-PXZ, with twisted donor-acceptor structures were designed and synthesized to study molecular design strategies of high-efficiency red TADF emitters. BPPZ-PXZ employs the strictest molecular restrictions to suppress energy loss and realizes red emission with a photoluminescence quantum yield (Φ_PL ) of 100±0.8 % and external quantum efficiency (EQE) of 25.2 % in a doped OLED. Its non-doped OLED has an EQE of 2.5 % owing to unavoidable intermolecular π-π interactions. mDPBPZ-PXZ releases two pyridine substituents from its fused acceptor moiety. Although mDPBPZ-PXZ realizes a lower EQE of 21.7 % in the doped OLED, its non-doped device shows a superior EQE of 5.2 % with a deep red/NIR emission at peak of 680 nm.

In vitro anticancer activity of AIEgens

Fluorogens with aggregation-induced emission (AIE) characteristics (AIEgens) possess unique optical properties, design flexibility, and multi-functional capabilities and have established their niche as smart materials since their discovery in 2001. In recent years, AIEgens have found varied applications in sensing, imaging, and therapy in biomedical research. In this work, we systematically and comprehensively investigate the in vitro anticancer activity of AIEgens. We report the high cytotoxicity of AIEgens against cancer cells, especially against cancer stem cells (CSCs) which show high resistance to existing therapeutic drug regimens. Furthermore, we explore the role of AIEgens as novel image-guided chemotherapy agents that offer a new avenue for efficient cancer treatment.

Multifunctional Two-Photon AIE Luminogens for Highly Mitochondria-Specific Bioimaging and Efficient Photodynamic Therapy

In recent years, photodynamic therapy (PDT) has drawn much attention as a noninvasive and safe cancer therapy method due to its fine controllability, good selectivity, low systemic toxicity, and minimal drug resistance in contrast to the conventional methods (for example, chemotherapy, radiotherapy, and surgery). However, some drawbacks still remain for the current organic photosensitizers such as low singlet oxygen (¹O₂) quantum yield, poor photostability, inability of absorption in the near-infrared (NIR) region, short excitation wavelength, and limited action radius of singlet oxygen, which will strongly limit the PDT treatment efficiency. As a consequence, the development of efficient photosensitizers with high singlet oxygen quantum yield, strong fluorescent emission in the aggregated state, excellent photostability, NIR excitation wavelength ranging in the biological transparency window, and highly specific targeting to mitochondria is still in great demand for the enhancement of PDT treatment efficiency. In this study, two new two-photon AIEgens TPPM and TTPM based on a rigid D-π-A skeleton have been designed and synthesized. Both AIEgens TPPM and TTPM show strong aggregation-induced emission (AIE) with the emission enhancement up to 290-folds, large two-photon absorption with the two-photon absorption cross section up to 477 MG, and highly specific targeting to mitochondria in living cells with good biocompatibility. They can serve as two-photon bioprobes for the cell and deep tissue bioimaging with a penetration depth up to 150 μm. Furthermore, high ¹O₂ generation efficiency with high ¹O₂ quantum yield under white light irradiation has been found for both TPPM and TTPM and high PDT efficiency to HeLa cells under white light irradiation has also been proven. To the best of our knowledge, AIEgens in this work constitute one of the strongest emission enhancements and one of the highest ¹O₂ generation efficiencies in the reported organic AIEgens so far. The great AIE feature, large two-photon absorption, high specificity to mitochondria in living cells, and high PDT efficiency to living cells as well as excellent photostability and biocompatibility of these novel AIEgens TPPM and TTPM reveal great potential in clinical applications of two-photon cell and tissue bioimaging and image-guided and mitochondria-targeted photodynamic cancer therapy.

A novel probe for colorimetric and near-infrared fluorescence detection of cysteine in aqueous solution, cells and zebrafish

Cysteine(Cys) is tightly related to physiological and pathological of human, and the imbalance of concentration of cysteine in the intracellular are associated with many diseases. Here, a novel NIR fluorescent probe TCF-Cys was designed and synthesized, and both the optimal excitation and emission wavelength of them were between 650 and 900 nm, that within the "optical window" of biological tissues. In aqueous solution, TCF-Cys, which with an acrylate extremity as a recognizing unit, exhibited excellent "turn-on" fluorescence response for Cys superior to other amino acids and thiols with a limit of detection of 0.1323 μM. Moreover, as an excellent naked-eye colorimetric indicator, TCF-Cys could effectively distinguishing the Cys, Hcy and GSH in aqueous solution through color change. Then, the response mechanism of TCF-Cys for Cys was revealed by TLC, ¹H NMR, HPLC, HRMS and DFT calculation. Finally, TCF-Cys was successfully employed to fluorescence specifically map of exogenous and endogenous Cys in living cells and zebrafish with low toxicity.