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The abnormal evolution of membrane-less organelles into amyloid fibrils is a causative factor in many neurodegenerative diseases. Fundamental research on evolving organic aggregates is thus instructive for understanding the root causes of these diseases. In-situ monitoring of evolving molecular aggregates with built-in fluorescence properties is a reliable approach to reflect their subtle structural variation. To increase the sensitivity of real-time monitoring, we presented organic aggregates assembled by TPAN-2MeO, which is a triphenyl acrylonitrile derivative. TPAN-2MeO showed a morphological evolution with distinct turn-on emission. Upon rapid nanoaggregation, it formed non-emissive spherical aggregates in the kinetically metastable state. Experimental and simulation results revealed that the weak homotypic interactions between the TPAN-2MeO molecules liberated their molecular motion for efficient non-radiative decay, and the strong heterotypic interactions between TPAN-2MeO and water stabilized the molecular geometry favorable for the non-fluorescent state. After ultrasonication, the decreased heterotypic interactions and increased homotypic interactions acted synergistically to allow access to the emissive thermodynamic equilibrium state with a decent photoluminescence quantum yield (PLQY). The spherical aggregates were eventually transformed into micrometer-sized blocklike particles. Under mechanical stirring, the co-assembly of TPAN-2MeO and Pluronic F-127 formed uniform fluorescent platelets, inducing a significant enhancement in PLQY. These results decipher the stimuli-triggered structural variation of organic aggregates with concurrent sensitive fluorescence response and pave the way for a deep understanding of the evolutionary events of biogenic aggregates.

The development of water-soluble aggregation-induced emission luminogens (AIEgens) emitting in the near-infrared (NIR) window holds promise for efficient biomedical applications. Nevertheless, synthesizing water-soluble counterparts of NIR AIEgens presents difficulties due to their intrinsic hydrophobic properties. To address this issue, researchers have developed various molecular design strategies to improve the water solubility of NIR AIEgens. The integration of hydrophilic groups and targeting moieties is a crucial aspect of achieving precise phototheranostics. Here, diverse approaches to attain water-soluble NIR AIEgens for biomedical applications are presented, and three commonly used strategies that involve decorating NIR AIEgens with positively or negatively charged groups, hydrophilic chains, and bioactive moieties are elaborated. These rational design strategies are believed to provide solutions for enhancing the water solubility and biological performance of NIR AIEgens in a single action. The remaining challenges and opportunities in this field are also discussed. The aim is to provide new insights into the design of water-soluble NIR AIEgens and inspire more researchers to make significant contributions to this promising research area. © 2023 The Authors. Small Science published by Wiley-VCH GmbH.

Breast cancer (BC) remains a significant global health challenge for women despite advancements in early detection and treatment. Isoliquiritigenin (ISL), a compound derived from traditional Chinese medicine, has shown potential as an anti-BC therapy, but its low bioavailability and poor water solubility restrict its effectiveness. In this study, we created theranostic nanoparticles consisting of ISL and a near-infrared (NIR) photosensitizer, TBPI, which displays aggregation-induced emission (AIE), with the goal of providing combined chemo- and photodynamic therapies (PDT) for BC. Initially, we designed an asymmetric organic molecule, TBPI, featuring a rotorlike triphenylamine as the donor and 1-methylpyridinium iodide as the acceptor, which led to the production of reactive oxygen species in mitochondria. We then combined TBPI with ISL and encapsulated them in DSPE-PEG-RGD nanoparticles to produce IT-PEG-RGD nanoparticles, which showed high affinity for BC, better intersystem crossing (ISC) efficiency, and Fo''rster resonance energy transfer (FRET) between TBPI and ISL. In both 4T1 BC cell line and a 4T1 tumor-bearing BC mouse model, the IT-PEG-RGD nanoparticles demonstrated excellent drug delivery, synergistic antitumor effects, enhanced tumor-killing efficacy, and reduced drug dosage and side effects. Furthermore, we exploited the optical properties of TBPI with ISL to reveal the release process and distribution of nanoparticles in cells. This study provides a valuable basis for further exploration of IT-PEG-RGD nanoparticles and their anticancer mechanisms, highlighting the potential of theranostic nanoparticles in BC treatment.

Tumor-targeted photodynamic therapy (PDT) is desirable as it can achieve efficient killing of tumor cells with no or less harm to normal cells. Herein, a facile molecular engineering strategy is developed for photosensitizers (PSs) with aggregation induced emission (AIE) characteristics and responsive properties to the acidic tumor microenvironment (TME). By the marriage of pH-sensitive sulfonamide moieties with AIE PSs, two near-infrared AIE luminogens called DBP-SPy and DBP-SPh are designed and synthesized. Both luminogens can form negatively charged nanoaggregates in the aqueous medium at physiological pH. The DBP-SPy nanoaggregates undergo surface charge conversion to become positive at pH close to the signature pH of TME, while DBP-SPh nanoaggregates show no such property. The endowed response to acidic TME enables the enhanced cellular uptake of DBP-SPy at pH = 6.8. By contrast, its cellular uptake is much sacrificed at pH 7.4. As a result, under white light irradiation, DBP-SPy nanoaggregates demonstrate a considerable photodynamic therapeutic effect on cancer cells in vitro and excellent tumor growth inhibition in vivo. Hence, this study not only provides an acidic TME-responsive AIE PS for precise PDT, but also inspires new design strategies for AIE-based theragnostic systems with targeting characteristics.

Specific bioconjugation for native primary amines is highly valuable for both chemistry and biomedical research. Despite all the efforts, scientists lack a proper strategy to achieve high selectivity for primary amines, not to mention the requirement of fast response in real applications. Herein, we report a chromone-based aggregation-induced emission (AIE) fluorogen called CMVMN as a self-reporting bioconjugation reagent for selective primary amine identification, and its applications for monitoring bioprocesses of amination and protein labeling. CMVMN is AIE-active and capable of solid-state sensing. Thus, its electrospun films are manufactured for visualization of amine diffusion and leakage process. CMVMN also shows good biocompatibility and potential mitochondria-staining ability, which provides new insight for organelle-staining probe design. Combined with its facile synthesis and good reversibility, CMVMN would not only show wide potential applications in biology, but also offer new possibilities for molecular engineering.

The integration of aggregation-induced emission luminogens (AIEgens) and inorganic constituents to generate multifunctional nanocomposites has attracted much attention because it couples the bright aggregate-state fluorescence of AIEgens with the diverse imaging modalities of inorganic constituents. Herein, a facile and universal strategy to prepare metal–phenolic-network (MPN)-coated AIE dots in a high encapsulation efficiency is reported. Through precise control on the nucleation of AIEgens and deposition of MPNs in tetrahydrofuran/water mixtures, termed as coacervation, core–shell MPN-coated AIE dots with bright emission are assembled in a one-pot fashion. The optical properties of MPN-coated AIE dots can be readily tuned by varying the incorporated AIEgens. Different metal ions, such as Fe3+, Ti4+, Cu2+, Ni2+, can be introduced to the nanoparticles. The MPN-coated AIE dots with a red-emissive AIEgen core are successfully used to perform magnetic resonance/fluorescence dual-modality imaging in a tumor-bearing mouse model and blood flow visualization in a zebrafish larva. It is believed that the present study provides a tailor-made nanoplatform to meet the individual needs of in vivo bioimaging. © 2022 The Authors. Advanced Science published by Wiley-VCH GmbH

Phototheranostic agents have thrived as promising tools for cancer theranostics because of the integration of sensitive in situ fluorescence imaging and effective multi-model synergistic therapy. However, how to manipulate the intangible photon energy transfer to balance the competitive radiative and nonradiative processes is still challenging. Although numerous phototheranostic molecules are reported, their complicated molecular design and tedious synthesis often stumble further their development. Herein, three simple molecules with electron donating−accepting structures are developed. The electron acceptor engineering on molecules by introducing acridinium unit gives rise to TPEDCAc with aggregation-induced second near-infrared emission (AIE NIR-II), high reactive oxygen species generation capability, and excellent photothermal conversion efficiency (44.8%) due to the drastic intramolecular motion of large acridinium rotor and balanced AIE effect. Experimental analysis and calculation on the controlled molecules suggested that large torsional angle and the strong electron-withdrawing ability of the acridinium unit are keys for NIR-II emission and balanced photodynamic/photothermal conversion. Impressively, the positively charged TPEDCAc shows mitochondria-targeting capability and high performance in in vivo multi-modal cancer theranostics under NIR laser irradiation. Hence, this work not only provides a single NIR-II AIE-based multi-modal cancer theranostic system but inspires new insights into future development of new theranostic platforms. © 2022 Wiley-VCH GmbH

Molecular aggregates with environmental responsive properties are desired for their wide practical applications such as bioprobes. Here, a series of smart near-infrared (NIR) luminogens for hyperlipidemia (HLP) diagnosis is reported. The aggregates of these molecules exhibit a twisted intramolecular charge-transfer effect in aqueous media, but aggregation-induced emission in highly viscous media due to the restriction of the intramolecular motion. These aggregates, which can autonomously respond to different environments via switching the aggregation state without changing their chemical structures are described, as “smart aggregates”. Intriguingly, these luminogens demonstrate NIR-II and NIR-III luminescence with ultralarge Stokes shifts (>950 nm). Both in vitro detection and in vivo imaging of HLP can be realized in a mouse model. Linear relationships exist between the emission intensity and multiple pathological parameters in blood samples of HLP patients. Thus, the design of smart aggregate facilitates rapid and accurate detection of HLP and provides a promising attempt in aggregate science.

The development of fluorescent probes based on the skeletal structure of small-molecule targeted anticancer drugs is promising for biomedical applications because these probes generally show trackable fluorescence and connatural bioactivity inherited from the parental anticancer drugs. By mimicking a classic estrogen receptor (ER) antagonist, namely, tamoxifen, we herein design and synthesize a photoactivatable luminogen with aggregation-induced emission and medicinal benefits. The probe is weakly emissive when it is selectively internalized by estrogen receptor-positive cells. Under photo-irradiation, its emission can be turned on to report the intracellular distribution. The cell viability assay suggests that the probe only exhibits cytotoxicity to ER-positive cells but negligible cytotoxicity to ER-negative cells. This study thus provides new access to targeted theranostic systems with photoactivity.

Fluorescence imaging in the second near-infrared window (NIR-II, 1000-1700 nm) using small-molecule dyes has high potential for clinical use. However, many NIR-II dyes suffer from the emission quenching effect and extremely low quantum yields (QYs) in the practical usage forms. The AIE strategy has been successfully utilized to develop NIR-II dyes with donor-acceptor (D-A) structures with acceptable QYs in the aggregate state, but there is still large room for QY improvement. Here, we rationally designed a NIR-II emissive dye named TPE-BBT and its derivative (TPEO-BBT) by changing the electron-donating triphenylamine unit to tetraphenylethylene (TPE). Their nanoparticles exhibited ultrahigh relative QYs of 31.5% and 23.9% in water, respectively. By using an integrating sphere, the absolute QY of TPE-BBT nanoparticles was measured to be 1.8% in water. Its crystals showed an absolute QY of 10.4%, which is the highest value among organic small molecules reported so far. The optimized D-A interaction and the higher rigidity of TPE-BBT in the aggregate state are believed to be the two key factors for its ultrahigh QY. Finally, we utilized TPE-BBT for NIR-II photoluminescence (PL) and chemiluminescence (CL) bioimaging through successive CL resonance energy transfer and Förster resonance energy transfer processes. The ultrahigh QY of TPE-BBT realized an excellent PL imaging quality in mouse blood vessels and an excellent CL imaging quality in the local arthrosis inflammation in mice with a high signal-to-background ratio of 130. Thus, the design strategy presented here brings new possibilities for the development of bright NIR-II dyes and NIR-II bioimaging technologies. © 2022 American Chemical Society.

Nonradiative decay invariably competes with radiative decay during the deexcitation process of matter. In the community of luminescence research, nonradiative decay has been deemed less attractive than radiative decay. However, all things in their being are good for something and so is nonradiative decay. As the molecular motion-facilitated nonradiative decay (MMFND) effect is inevitable in photophysical processes, it provides a new avenue to convert the harvested light energy into exploitable forms by harnessing molecular motion. In many cases, active molecular motion enables thermal deactivation from excited states. In this Minireview, recent advances in photothermal and photoacoustic systems with MMFND character are summarized. We believe that this presentation of the rational engineering of molecular motion for efficient photothermal generation will deepen the understanding of the relationship between molecular motion and nonradiative decay and navigate people to rethink the positive aspects of nonradiative decay for the establishment of new light-controllable techniques. © 2022 Wiley-VCH GmbH.

Efficient theranostic systems can realize better outcomes in disease treatment because of precise diagnosis and the concomitant effective therapy. Aggregation-induced emission luminogens (AIEgens) are a unique type of organic emitters with intriguing photophysical properties in the aggregate state. Among the AIEgens studied for biomedical applications, so far, metal-based AIE systems have shown great potential in theranostics due to the enhanced multimodal bioimaging ability and therapeutic effect. This research field has been growing rapidly, and many rationally designed systems with promising activities to cancer and other diseases have been reported recently. In this review, we summarized the recent progress of metal-based AIE materials in bioimaging and biological theranostics, and deciphered the pertinent design strategies. We hope that this review can offer new insights into the development of this growing field. © 2021 Wiley-VCH GmbH

Efficient theranostic systems can realize better outcomes in disease treatment because of precise diagnosis and the concomitant effective therapy. Aggregation-induced emission luminogens (AIEgens) are a unique type of organic emitters with intriguing photophysical properties in the aggregate state. Among the AIEgens studied for biomedical applications, so far, metal-based AIE systems have shown great potential in theranostics due to the enhanced multimodal bioimaging ability and therapeutic effect. This research field has been growing rapidly, and many rationally designed systems with promising activities to cancer and other diseases have been reported recently. In this review, we summarized the recent progress of metal-based AIE materials in bioimaging and biological theranostics, and deciphered the pertinent design strategies. We hope that this review can offer new insights into the development of this growing field. © 2021 Wiley-VCH GmbH

The development of dark pro-aggregation-induced-emission luminogens (pro-AIEgens) based on the solid-state intramolecular motion–caused quenching effect has been rarely reported in biochemical analysis. Herein, an azo-conjugated pro-AIEgen derived from tetraphenylethene is constructed. Due to the active molecular motion of the azo bond, it retains a nonemissive property in both solution and solid forms. The obtained pro-AIEgen can be internalized by living cells and undergo reductase-modulated derotation under hypoxia to emit light. It shows increasing fluorescence when the intracellular oxygen concentration becomes lower, making it a potential probe to sense the hypoxic environment. The present probe can also visualize the hypoxic environment created by photodynamic therapy treatment.

Hypoxia-responsive fluorescent probes have emerged as a novel scaffold for tumor diagnosis. However, dilemma often exists between simple synthesis and high water solubility in traditional probes. Owing to the intrinsic property of N-oxides, herein, a new strategy is proposed to design and synthesize probes for in vitro hypoxia imaging. Equipped with tetraphenylethene (TPE), the N-oxides exhibit aggregation-induced emission characteristics and emit no light in aqueous solutions. Interestingly, the N-oxides can be reduced by ferrous ions in different rates. The aggregation of the resulting hydrophobic TPE residues restricts the intramolecular motions of the molecules, which “turns-on” their fluorescence. The NO covalent bond of one molecule can be specifically cleaved by cellular reductase overexpressed under hypoxic conditions, and thus turn-on hypoxia imaging in vitro is achieved. The new strategy to design hypoxia imaging probes is extremely valuable and has great potential for application in tumor diagnosis.