Facile synthesis of AIEgens with wide color tunability for cellular imaging and therapy

A lipid activated color switchable probe for the imaging of diseased aortic valves

Lipid deposition has been considered one of the key factors in the occurrence of valvular heart disease (VHD) and a great potential target for the diagnosis of VHD. However, the development of lipid imaging technologies and efficient lipid specific probes is in urgent demand. In this work, we have prepared a lipid droplets (LDs) targeted fluorescence probe CPTM based on a push-pull electronic structure for the imaging of diseased aortic valves. CPTM showed obvious twisted intramolecular charge transfer (TICT) effect and its emission changed from 600 nm in water to 508 nm in oil. CPTM not only exhibited good biocompatibility and high photostability, but also impressive LDs specific imaging performance in human primary valvular interstitial cells and human diseased aortic valves. Moreover, the dynamic changes of intracellular LDs could be monitor in real-time after staining with CPTM. These results were expected to offer new ideals for the designing of novel LDs specific probes for further bioimaging applications.

Deep blue emitting dual state fluorescent triphenylamine-dicyclohexylurea derivative: Multi-stimuli responsive fluorescence switching and methanol/water sensing

A new deep blue emissive organic fluorophore (N-cyclohexyl-N-(cyclohexylcarbamoyl)-4-(diphenylamino)benzamide (NCDPB)) was designed and synthesized, which showed strong fluorescence both in solution and solid-state. Solid-state structural analysis of NCDPB revealed non-planar twisted molecular conformation with extended hydrogen bonding between the amide functionalities. The propeller shaped triphenylamine (TPA) and non-planar cyclohexyl unit prevented close π…π stacking and produced strong deep blue emission in the solid state (λmax = 400 nm, quantum yield (Φf) = 12.6 %). NCDPB also exhibited strong solvent polarity dependent tunable emission in solution (λmax = 402-462 nm, Φf = 1.15 (compared to quinine sulphate)). NCDPB showed reversible fluorescence switching between two fluorescence states upon mechanical crushing and heating/solvent exposure. Mechanical crushing caused red shifting of fluorescence from 400 to 447 nm and heating/solvent exposure reversed the fluorescence. Further, NCDPB also displayed off-on reversible/self-reversible fluorescence switching upon exposure to trifluoracetic acid (TFA) and NH3. The repeated fluorescence switching cycles indicated high reversibility without any significant change of fluorescence intensity. The drastically different fluorescence of NCDPB in CH3OH and EtOH was utilized to distinguish them and monitor CH3OH contamination in ethanol and benzene. It showed limit of detection (LOD) of methanol up to 0.25 % and 7 % in benzene and ethanol, respectively. The water sensitive fluorescence modulation of NCDPB in organic solvents was used to sensing water contamination in common organic solvents. Thus, integration of twisted TPA with H-bonding urea produced dual state emitting organic fluorophore with multi-responsive fluorescence switching and solvent sensing.

Dynamic Imaging of Lipid Droplets in Cells and Tissues by Using Dioxaborine Barbiturate-Based Fluorogenic Probes

Lipids are essential for various cellular functions, including energy storage, membrane flexibility, and signaling molecule production. Maintaining proper lipid levels is important to prevent health problems such as cancer, neurodegenerative disorders, cardiovascular diseases, obesity, and diabetes. Monitoring cellular lipid droplets (LDs) in real-time with high resolution can provide insights into LD-related pathways and diseases owing to the dynamic nature of LDs. Fluorescence-based imaging is widely used for tracking LDs in live cells and animal models. However, the current fluorophores have limitations such as poor photostability and high background staining. Herein, we developed a novel fluorogenic probe based on a push-pull interaction combined with aggregation-induced emission enhancement (AIEE) for dynamic imaging of LDs. Probe 1 exhibits favorable membrane permeability and spectroscopic characteristics, allowing specific imaging of cellular LDs and time-lapse imaging of LD accumulation. This probe can also be used to examine LDs in fruit fly tissues in various metabolic states, serving as a highly versatile and specific tool for dynamic LD imaging in cellular and tissue environments.

A Rational Design of Electrochemically and Photophysically Tunable Triarylamine Luminophores by Consecutive (Pseudo-)Four-Component Syntheses

The concatenation of Suzuki coupling and two-fold Buchwald-Hartwig amination in sequentially palladium-catalyzed consecutive multicomponent syntheses paves a concise, convergent route to diversely functionalized para-biaryl-substituted triarylamines (p-bTAAs) from simple, readily available starting materials. An extensive library of p-bTAAs permits comprehensive investigations of their electronic properties by absorption and emission spectroscopy, cyclic voltammetry, and quantum chemical calculations, which contribute to a deep understanding of their electronic structure. The synthesized p-bTAAs exhibit tunable fluorescence from blue to yellow upon photonic excitation with quantum yields up to 98 % in solution and 92 % in the solid state. Furthermore, a pronounced bathochromic shift of the emission maxima by increasing solvent polarity indicates positive emission solvatochromism. Aggregation-induced enhanced emission (AIEE) in dimethyl sulfoxide (DMSO)/water mixtures causes the formation of intensely blue fluorescent aggregates. Cyclic voltammetry shows reversible first and second oxidations of p-bTAAs at low potentials, which are tunable by variation of the introduced para substituents. 3D Hammett plots resulting from the correlation of oxidation potentials and emission maxima with electronic substituent parameters emphasize the rational design of tailored p-bTAAs with predictable electrochemical and photophysical properties.

Thiophene Stability in Photodynamic Therapy: A Mathematical Model Approach

Thiophene-containing photosensitizers are gaining recognition for their role in photodynamic therapy (PDT). However, the inherent reactivity of the thiophene moiety toward singlet oxygen threatens the stability and efficiency of these photosensitizers. This study presents a novel mathematical model capable of predicting the reactivity of thiophene toward singlet oxygen in PDT, using Conceptual Density Functional Theory (CDFT) and genetic programming. The research combines advanced computational methods, including various DFT techniques and symbolic regression, and is validated with experimental data. The findings underscore the capacity of the model to classify photosensitizers based on their photodynamic efficiency and safety, particularly noting that photosensitizers with a constant rate 1000 times lower than that of unmodified thiophene retain their photodynamic performance without substantial singlet oxygen quenching. Additionally, the research offers insights into the impact of electronic effects on thiophene reactivity. Finally, this study significantly advances thiophene-based photosensitizer design, paving the way for therapeutic agents that achieve a desirable balance between efficiency and safety in PDT.

Photophysical Analysis of Aggregation-Induced Emission (AIE) Luminogens Based on Triphenylamine and Thiophene: Insights into Emission Behavior in Solution and PMMA Films

Aggregation-Induced Emission (AIE) luminogens have garnered significant interest due to their distinctive applications in different applications. Among the diverse molecular architectures, those based on triphenylamine and thiophene hold prominence. However, a comprehensive understanding of the deactivation mechanism both in solution and films remains lacking. In this study, we synthesized and characterized spectroscopically two AIE luminogens: 5-(4-(bis(4-methoxyphenyl)amino)phenyl)thiophene-2-carbaldehyde (TTY) and 5'-(4-(bis(4-methoxyphenyl)amino)phenyl)-[2,2'-bithiophene]-5-carbaldehyde (TTO). Photophysical and theoretical analyses were conducted in both solution and PMMA films to understand the deactivation mechanism of TTY and TTO. In diluted solutions, the emission behavior of TTY and TTO is influenced by the solvent, and the deactivation of the excited state can occur via locally excited (LE) or twisted intramolecular charge transfer (TICT) state. In PMMA films, rotational and translational movements are constrained, necessitating emission solely from the LE state. Nevertheless, in the PMMA film, excimers-like structures form, resulting in the emergence of a longer wavelength band and a reduction in emission intensity. The zenith of emission intensity occurs when molecules are dispersed at higher concentrations within PMMA, effectively diminishing the likelihood of excimer-like formations. Luminescent Solar Concentrators (LSC) were fabricated to validate these findings, and the optical efficiency was studied at varying concentrations of luminogen and PMMA.

B-embedded disulfide-bridged π-conjugated compounds: structures and optical tuning

Two novel B-embedded disulfide-bridged π-conjugated compounds (BS-CZ and BS-N) bearing different electron donor groups (phenyl carbazole and triphenylamine) have been prepared and show different optical mechanisms. The compound BS-CZ exhibits significant multiple resonance thermal activation delayed fluorescence (MR-TADF) properties with a small singlet-triplet energy gap (ΔEST = 0.16 eV) and a narrow half-peak full width (FWHM = 33 nm), while the compound BS-N shows traditional fluorescence luminescence (FL) characteristics with a larger ΔEST (0.28 eV) and FWHM (57 nm). Time-dependent density functional theory (TD-DFT) calculations show that the lowest excited singlet state (S1) of the compound BS-CZ exhibits local excited (LE) state characteristics, while the charge transfer (CT) state characteristics can be found in S1 of the compound BS-N. Considering good optical performance, the compound BS-CZ is used as an emitting layer of the organic light-emitting diode device and achieved saturated blue emission (473 nm) with a narrow FWHM (39 nm), and CIE color coordinates of (0.12, 0.21). This work provides an important strategy for the optical mechanism regulation and photoelectric applications of B-embedded disulfide-bridged π-conjugated molecules.

Endoplasmic Reticulum-Targeted Aggregation-Induced Emission Luminogen for Synergetic Tumor Ablation with Glibenclamide

Photodynamic therapy based on fluorescence illumination of subcellular organelles and in situ bursts of reactive oxygen species (ROS) has been recognized as a promising strategy for cancer theranostics. However, the short life of ROS and unclarified anticancer mechanism seriously restrict the application. Herein, we rationally designed and facilely synthesized a 2,6-dimethylpyridine-based triphenylamine (TPA) derivative TPA-DMPy with aggregation-induced emission (AIE) features and production of type-I ROS. Except for its selective binding to the endoplasmic reticulum (ER), TPA-DMPy, in synergy with glibenclamide, a medicinal agent used against diabetes, induced significant apoptosis of cancer cells in vitro and in vivo. Additionally, TPA-DMPy greatly incited the release of calcium from ER upon light irradiation to further aggravate the depolarization of ER membrane potential caused by glibenclamide, thus inducing fatal ER stress and crosstalk between ER and mitochondria. Our study extends the biological design and application of AIE luminogens and provides new insights into discovering novel anticancer targets and agents.

A new class of teraryl-based AIEgen for highly selective imaging of intracellular lipid droplets and its detection in advanced-stage human cervical cancer tissues

Lipid droplets (LDs) have drawn much attention in recent years. They serve as the energy reservoir of cells and also play an important role in numerous physiological processes. Furthermore, LDs are found to be associated with several pathological conditions, including cancer and diabetes mellitus. Herein, we report a new class of teraryl-based donor-acceptor-appended aggregation-induced emission luminogen (AIEgen), 6a, for selective staining of intracellular LDs in in vitro live 3T3-L1 preadipocytes and the HeLa cancer cell line. In addition, AIEgen 6a was found to be capable of staining and quantifying the LD accumulation in the tissue sections of advanced-stage human cervical cancer patients. Unlike commercial LD staining dyes Nile Red, BODIPY and LipidTOX, AIEgen 6a showed a high Stokes shift (195 nm), a good fluorescence lifetime decay of 12.7 ns, and LD staining persisting for nearly two weeks.

Synthesis and Characterization of Tetraphenylethene AIEgen-Based Push-Pull Chromophores for Photothermal Applications: Could the Cycloaddition-Retroelectrocyclization Click Reaction Make Any Molecule Photothermally Active?

Three new tetraphenylethene (TPE) push-pull chromophores exhibiting strong intramolecular charge transfer (ICT) are described. They were obtained via [2 + 2] cycloaddition-retroelectrocyclization (CA-RE) click reactions on an electron-rich alkyne-tetrafunctionalized TPE (TPE-alkyne) using both 1,1,2,2-tetracyanoethene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄-TCNQ) as electron-deficient alkenes. Only the starting TPE-alkyne displayed significant AIE behavior, whereas for TPE-TCNE, a faint effect was observed, and for TPE-TCNQ and TPE-F₄-TCNQ, no fluorescence was observed in any conditions. The main ICT bands that dominate the UV-Visible absorption spectra underwent a pronounced red-shift beyond the near-infrared (NIR) region for TPE-F₄-TCNQ. Based on TD-DFT calculations, it was shown that the ICT character shown by the compounds exclusively originated from the clicked moieties independently of the nature of the central molecular platform. Photothermal (PT) studies conducted on both TPE-TCNQ and TPE-F4-TCNQ in the solid state revealed excellent properties, especially for TPE-F4-TCNQ. These results indicated that CA-RE reaction of TCNQ or F₄-TCNQ with donor-substituted are promising candidates for PT applications.

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

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

Machine-learning screening of luminogens with aggregation-induced emission characteristics for fluorescence imaging

Due to the excellent biocompatible physicochemical performance, luminogens with aggregation-induced emission (AIEgens) characteristics have played a significant role in biomedical fluorescence imaging recently. However, screening AIEgens for special applications takes a lot of time and efforts by using conventional chemical synthesis route. Fortunately, artificial intelligence techniques that could predict the properties of AIEgen molecules would be helpful and valuable for novel AIEgens design and synthesis. In this work, we applied machine learning (ML) techniques to screen AIEgens with expected excitation and emission wavelength for biomedical deep fluorescence imaging. First, a database of various AIEgens collected from the literature was established. Then, by extracting key features using molecular descriptors and training various state-of-the-art ML models, a multi-modal molecular descriptors strategy has been proposed to extract the structure-property relationships of AIEgens and predict molecular absorption and emission wavelength peaks. Compared to the first principles calculations, the proposed strategy provided greater accuracy at a lower computational cost. Finally, three newly predicted AIEgens with desired absorption and emission wavelength peaks were synthesized successfully and applied for cellular fluorescence imaging and deep penetration imaging. All the results were consistent successfully with our expectations, which demonstrated the above ML has a great potential for screening AIEgens with suitable wavelengths, which could boost the design and development of novel organic fluorescent materials.

Characterization Techniques of Polymer Aging: From Beginning to End

Polymers have been widely applied in various fields in the daily routines and the manufacturing. Despite the awareness of the aggressive and inevitable aging for the polymers, it still remains a challenge to choose an appropriate characterization strategy for evaluating the aging behaviors. The difficulties lie in the fact that the polymer features from the different aging stages require different characterization methods. In this review, we present an overview of the characterization strategies preferable for the initial, accelerated, and late stages during polymer aging. The optimum strategies have been discussed to characterize the generation of radicals, variation of functional groups, substantial chain scission, formation of low-molecular products, and deterioration in the polymers' macro-performances. In view of the advantages and the limitations of these characterization techniques, their utilization in a strategic approach is considered. In addition, we highlight the structure-property relationship for the aged polymers and provide available guidance for lifetime prediction. This review could allow the readers to be knowledgeable of the features for the polymers in the different aging stages and provide access to choose the optimum characterization techniques. We believe that this review will attract the communities dedicated to materials science and chemistry.

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.

3-Aryl-5-aminobiphenyl Substituted [1,2,4]triazolo[4,3-c]quinazolines: Synthesis and Photophysical Properties

Amino-[1,1']-biphenyl-containing 3-aryl-[1,2,4]triazolo[4,3-c]quinazoline derivatives with fluorescent properties have been designed and synthesized. The type of annelation of the triazole ring to the pyrimidine one has been unambiguously confirmed by means of an X-ray diffraction (XRD) method; the molecules are non-planar, and the aryl substituents form the pincer-like conformation. The UV/Vis and photoluminescent properties of target compounds were investigated in two solvents of different polarities and in a solid state. The samples emit a broad range of wavelengths and display fluorescent quantum yields of up to 94% in toluene solutions. 5-(4'-Diphenylamino-[1,1']-biphenyl-4-yl)-3-(4-(trifluoromethyl)phenyl)-[1,2,4]triazolo[4,3-c]quinazoline exhibits the strongest emission in toluene and a solid state. Additionally, the solvatochromic properties were studied for the substituted [1,2,4]triazolo[4,3-c]quinazolines. Moreover, the changes in absorption and emission spectra have been demonstrated upon the addition of water to MeCN solutions, which confirms aggregate formation, and some samples were found to exhibit aggregation-induced emission enhancement. Further, the ability of triazoloquinazolines to detect trifluoroacetic acid has been analyzed; the presence of TFA induces changes in both absorption and emission spectra, and acidochromic behavvior was observed for some triazoloquinazoline compounds. Finally, electronic-structure calculations with the use of quantum-chemistry methods were performed for synthesized compounds.

Polymersomes with Red/Near-Infrared Emission and Reactive Oxygen Species Generation

In photodynamic therapy (PDT), the uses of nanoparticles bearing photosensitizers (PSs) can overcome some of the drawbacks of using a PS alone (e.g., poor water solubility and low tumor selectivity). However, numerous nano-formulations are developed by physical encapsulation of PSs through Van der Waals interactions, which have not only a limited load efficiency but also some in vivo biodistribution problems caused by leakage or burst release. Herein, polymersomes made from an amphiphilic block copolymer, in which a PS with aggregation-induced emission (AIE-PS) is covalently attached to its hydrophobic poly(amino acid) block, are reported. These AIE-PS polymersomes dispersed in aqueous solution have a high AIE-PS load efficiency (up to 46% as a mass fraction), a hydrodynamic diameter of 86 nm that is suitable for in vivo applications, and an excellent colloidal stability for at least 1 month. They exhibit a red/near-infrared photoluminescence and ability to generate reactive oxygen species (ROS) under visible light. They are non-cytotoxic in the dark as tested on Hela cells up to concentration of 100 µm. Benefiting from colloidal stability, AIE property and ROS generation capability, such a family of polymersomes can be great candidates for image-guided PDT.

Near-infrared AIE-active phosphorescent iridium(III) complex for mitochondria-targeted photodynamic therapy

Mitochondria-targeted photodynamic therapy (PDT) has recently been recognized as a promising strategy for effective cancer treatment. In this work, a mitochondria-targeted near-infrared (NIR) aggregation-induced emission (AIE)-active phosphorescent Ir(III) complex (Ir1) is reported with highly favourable mitochondria-targeted bioimaging and cancer PDT properties. Complex Ir1 has strong absorption in the visible light region (∼500 nm) and can effectively produce singlet oxygen (¹O₂) under green light (525 nm) irradiation. It preferentially accumulates in the mitochondria of human breast cancer MDA-MB-231 cells as revealed by colocalization analysis. Complex Ir1 displays high phototoxicity toward human breast cancer MDA-MB-231 cells and mouse breast cancer 4T1 cells. Complex Ir1 induces reactive oxygen species (ROS) production, mitochondrial dysfunction, and endoplasmic reticulum (ER) stress in MDA-MB-231 cells upon photoirradiation, leading to apoptotic cell death. The favorable PDT performance of Ir1in vivo has been further demonstrated in tumour-bearing mice. Together, the results suggest that Ir1 is a promising photosensitizer for mitochondria-targeted imaging and cancer phototherapy.

AIE Polymer Micelle/Vesicle Photocatalysts Combined with Native Enzymes for Aerobic Photobiocatalysis

Biocatalytic transformation has attracted increasing attention in the green synthesis of chemicals due to the diversity of enzymes, their high catalytic activities and specificities, and environmentally benign conditions. Most redox enzymes in nature are dependent on nicotinamide cofactors like β-nicotinamide adenine dinucleotide (NAD⁺)/reduced nicotinamide adenine dinucleotide (NADH). The use of solar energy, especially visible light, in the regeneration of cofactors through the combination of photocatalysis and biocatalysis provides an extraordinary opportunity to make complete green processes. However, the combination of photocatalysts and enzymes has been challenged by the rapid degradation and deactivation of the enzymatic material by photogenerated reactive oxygen species (ROS). Here, we design core-shell structured polymer micelles and vesicles with aggregation-induced emission (AIE) as visible-light-mediated photocatalysts for highly stable and recyclable photobiocatalysis under aerobic conditions. NAD⁺ from NADH can be efficiently regenerated by the photoactive hydrophobic core of polymer micelles and the hydrophobic membrane of polymer vesicles, while the enzymatic material (glucose 1-dehydrogenase) is screened from the attack of photogenerated ROS by the hydrophilic surface layer of polymer colloids. After at least 10 regeneration cycles, the enzyme keeps its active state; meanwhile, polymer micelles and vesicles maintain their photocatalytic activity. These polymer colloids show the potential to be developed for the implementation of industrially relevant photobiocatalytic systems.

Nanoscopic evaluation on mitochondrial ultrastructures by regulating reactive oxygen species productivity within terpyridyl Zn(II) complexes with different alkyl chain lengths

Mitochondria targeting complexes are widely utilized as photosensitizers in photodynamic therapy. However, the mechanisms by which they regulate reactive oxygen species (ROS) production at the molecular level and their influence on intracellular mitochondrial signaling and ultrastructures remain rarely studied. Herein, we present two terpyridyl Zn(II) complexes with different side alkyl chain lengths (Zn-2C and Zn-6C) that lead to low and high ROS productivities in vitro, respectively. Both complexes could enter live cells effectively with minimal dark toxicity and accumulate preferably in the mitochondria. We also demonstrated that Zn-6C, with more efficient ROS productivity, could significantly downregulate the caspase signaling pathway but showed no evident influence on mitochondrial membrane proteins. We also highlighted and compared the mitochondrial ultrastructural variations during such a process by stimulated emission depletion (STED) super-resolution nanoscopy.

Molecularly Engineered Unparalleled Strength and Supertoughness of Poly(urea-urethane) with Shape Memory and Clusterization-Triggered Emission

To address the challenge of realizing multifunctional polymers simultaneously exhibiting high strength and high toughness through molecular engineering, ultrastrong and supertough shape-memory poly(urea-urethane) (PUU) is fabricated by regulating: i) the reversible cross-links composed of rigid units and multiple hydrogen bonds, and ii) the molecular weight of soft segments. The optimal material exhibits an unparalleled strength of 84.2 MPa at a large elongation at a break of 925.6%, a superior toughness of 322.8 MJ m^-3 , and remarkable fatigue resistance without fracture. The repeated stretching of this material induces an irreversible deformation, which, however, can be rapidly recovered by heating. Moreover, all samples are capable of temporary shape fixation at -40 °C (recovering the original shape at 30 °C) and exhibit blue fluorescence when excited at the optimum wavelength, which is ascribed to clusterization-triggered emission (CTE) due to the formation of microphase-separation structures. Thus, the adopted approach provides a solution to a long-standing problem and paves the way to the realization of intrinsically luminescent shape-memory materials exhibiting both ultrahigh strength and ultrahigh toughness.

Self-cleaning wearable masks for respiratory infectious pathogen inactivation by type I and type II AIE photosensitizer

Although face masks as personal protective equipment (PPE) are recommended to control respiratory diseases with the on-going COVID-19 pandemic, improper handling and disinfection increase the risk of cross-contamination and compromise the effectiveness of PPE. Here, we prepared a self-cleaning mask based on a highly efficient aggregation-induced emission photosensitizer (TTCP-PF₆) that can destroy pathogens by generating Type I and Type II reactive oxygen species (ROS). The respiratory pathogens, including influenza A virus H1N1 strain and Streptococcus pneumoniae (S. pneumoniae) can be inactivated within 10 min of ultra-low power (20 W/m²) white light or simulated sunlight irradiation. This TTCP-PF₆-based self-cleaning strategy can also be used against other airborne pathogens, providing a strategy for dealing with different microbes.

AIEgen-Peptide Bioprobes for the Imaging of Organelles

Organelles are important subsystems of cells. The damage and inactivation of organelles are closely related to the occurrence of diseases. Organelles’ functional activity can be observed by fluorescence molecular tools. Nowadays, a series of aggregation-induced emission (AIE) bioprobes with organelles-targeting ability have emerged, showing great potential in visualizing the interactions between probes and different organelles. Among them, AIE luminogen (AIEgen)-based peptide bioprobes have attracted more and more attention from researchers due to their good biocompatibility and photostability and abundant diversity. In this review, we summarize the progress of AIEgen-peptide bioprobes in targeting organelles, including the cell membrane, nucleus, mitochondria, lysosomes and endoplasmic reticulum, in recent years. The structural characteristics and biological applications of these bioprobes are discussed, and the development prospect of this field is forecasted. It is hoped that this review will provide guidance for the development of AIEgen-peptide bioprobes at the organelles level and provide a reference for related biomedical research.

Advances in the Structural Strategies of the Self-Assembly of Photoresponsive Supramolecular Systems

Photosensitive supramolecular systems have garnered attention due to their potential to catalyze highly specific tasks through structural changes triggered by a light stimulus. The tunability of their chemical structure and charge transfer properties provides opportunities for designing and developing smart materials for multidisciplinary applications. This review focuses on the approaches reported in the literature for tailoring properties of the photosensitive supramolecular systems, including MOFs, MOPs, and HOFs. We discuss relevant aspects regarding their chemical structure, action mechanisms, design principles, applications, and future perspectives.

Unusual Electron Donor-Acceptor sequenced NIR AIEgen for Highly Efficient Mitochondria-Targeted Cancer Cell Photodynamic Therapy

Photodynamic therapy (PDT) is recognized to be a promising strategy for anticancer treatment. Considering the progressive application of PDT in clinical trials, highly efficient and photostable photosensitizers (PSs) are in strong demand. Aggregation-induced emission (AIE) based PSs are promising phototheranostic materials for tumor imaging and PDT due to their high fluorescence efficiency and photostability. Herein, a mitochondria-targeted PS, TPA-2TCP with AIE characteristics is developed by adopting an acceptor-π-donor-π-acceptor (A-π-D-π-A) structure. The untypical sequence of the electron donors and electron acceptors endows the derived AIE PS with evident redshift of the absorption and emission, and efficient generation of reactive oxygen species. With the positively charged pyridinium groups, nanoparticulated AIE PS (TPA-2TCP NPs) exhibits high cell binding efficiency towards 4T1 breast cancer cells, leading to the massive cell death via the apoptotic pathway under white light irradiation, demonstrating its potential application in cancer imaging and PDT.

Highly Deep‐Blue Luminescent Twisted Diphenylamino Terphenyl Emitters by Bromine‐Lithium Exchange Borylation‐Suzuki Sequence

Four novel intensively blue luminescent chromophores were readily synthesized by bromine‐lithium exchange borylation‐Suzuki (BLEBS) sequence in moderate to good yields. Their electronic properties were studied by absorption and emission spectroscopy and quantum chemical calculations revealing deep‐blue emission in solution as well as in the solid state and upon embedding into a PMMA (polymethylmethacrylate) matrix with small FWHM (full width at half maximum) values and CIE y values smaller than 0.1. Moreover, high photoluminescence quantum yields (PLQY), partially close to unity, are found.

A Novel Fluoro-Pyrazine-Bridged Donor-Accepter-Donor Fluorescent Probe for Lipid Droplet-Specific Imaging in Diverse Cells and Superoxide Anion Generation

PURPOSE

Lipid droplets (LDs) are dynamic organelles which associated with many metabolic processes. Reliable long-term imaging of LD is of great importance in LD-based therapy and research. Conventional fluorescent probes suffer from poor photostability and difficulty of preparation, which compromise their LD imaging ability. In this study, we aim to provide a novel and universal fluorescent probe for LD-specific imaging in both eukaryotic and prokaryotic cells. The versatile and potential applications of the probe were also evaluated.

METHODS

We used one-step Suzuki coupling reaction to synthesize a fluoro-pyrazine-bridged donor-acceptor-donor fluorescent probe (T-FP-T). The fluorescent properties and stability of T-FP-T were detected. Then, LD-specific imaging and dynamic movement tracking capabilities of T-FP-T were studied in fungus, bacteria, plant and animal tissues. The biosafety and photodynamic toxicity of the probe under different light irradiation were characterized.

RESULTS

T-FP-T showed large Stokes shift, superior brightness, excellent photostability, low toxicity. T-FP-T exhibited significant overlaps with adipophilin antibody or the commercial LD probe (LipidSpot™) in the cytoplasm, but not with Mitotracker red, Lysotracker red and Peroxisome Labeling dye. Moreover, T-FP-T also showed efficient superoxide anion generation capability under white LED light irradiation. The viability of Hela cells co-treated with T-FP-T and 1-h white LED light irradiation decreased to 62%.

CONCLUSIONS

All these outstanding capabilities make T-FP-T a new efficient LD-specific imaging probe. The generated superoxide anion from T-FP-T under white LED light irradiation could cause obvious cell death, which will inspire broad study in LD-targeted photodynamic therapy.

The fast-growing field of photo-driven theranostics based on aggregation-induced emission

Photo-driven theranostics, also known as phototheranostics, relying on the diverse excited-state energy conversions of theranostic agents upon photoexcitation represents a significant branch of theranostics, which ingeniously integrate diagnostic imaging and therapeutic interventions into a single formulation. The combined merits of photoexcitation and theranostics endow photo-driven theranostics with numerous superior features. The applications of aggregation-induced emission luminogens (AIEgens), a particular category of fluorophores, in the field of photo-driven theranostics have been intensively studied by virtue of their versatile advantageous merits of favorable biocompatibility, tuneable photophysical properties, unique aggregation-enhanced theranostic (AET) features, ideal AET-favored on-site activation ability and ready construction of one-for-all multimodal theranostics. This review summarised the significant achievements of photo-driven theranostics based on AIEgens, which were detailedly elaborated and classified by their diverse theranostic modalities into three groups: fluorescence imaging-guided photodynamic therapy, photoacoustic imaging-guided photothermal therapy, and multi-modality theranostics. Particularly, the tremendous advantages and individual design strategies of AIEgens in pursuit of high-performance photosensitizing output, high photothermal conversion and multimodal function capability by adjusting the excited-state energy dissipation pathways are emphasized in each section. In addition to highlighting AIEgens as promising templates for modulating energy dissipation in the application of photo-driven theranostics, current challenges and opportunities in this field are also discussed.

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...

Optimizing Comprehensive Performance of Aggregation-Induced Emission Nanoparticles through Molecular Packing Modulation for Multimodal Image-Guided Synergistic Phototherapy

Fluorescent nanoparticles (NPs) with aggregation-induced emission (AIE) characteristics hold remarkable potential for image-guided phototherapy. The molecular packing is the key point for optimizing the performance of AIE luminogens (AIEgens) in the aggregated or solid state. However, so far, the packing mode of AIEgens in NPs is still vague, causing some challenges for understanding the relationship between the photophysical property and packing mode, as well as further optimizing the performance of NPs for biomedical applications. In this contribution, by simply controlling the length of alkoxy chains in the donor-acceptor conjugated OPTPA, a packing balance between the twisted molecular structure and effective π-conjugation is actualized. Subsequently, the possibility of amorphous-crystalline transition of AIEgens in the polymer-encapsulated NPs is presented for the first time, and the comprehensive performance of NPs is further optimized. Both in vitro and in vivo experiments indicate that crystalline AIEgen-based NPs are remarkably effective in trimodal imaging-guided synergistic phototherapy.

Metal-Based Aggregation-Induced Emission Theranostic Systems

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.

Recent advances in assembled AIEgens for image-guided anticancer therapy

Image-guided therapy, with simultaneous imaging and therapy functions, has the potential to greatly enhance the therapeutic efficacy of anticancer therapy, and reduce the incidence of side effects. Fluorescence imaging has the advantages of easy operation, abundant signal, high contrast, and fast response for real-time and non-invasive tracking. Luminogens with aggregation-induced emission characteristics (AIEgens) can emit strong luminescence in an aggregate state, which makes them ideal materials to construct applicative fluorophores for fluorescence imaging. The opportunity for image-guided cancer treatment has inspired researchers to explore the theranostic application of AIEgens combined with other therapy methods. In recent years, many AIEgens with efficient photosensitizing or photothermal abilities have been designed by precise molecular engineering, with superior performance in image-guided anticancer therapy. Owing to the hydrophobic property of most AIEgens, an assembly approach has been wildly utilized to construct biocompatible AIEgen-based nanostructures in aqueous systems, which can be used for image-guided anticancer therapy. In the present review, we summarize the recent advances in the assembled AIEgens for image-guided anticancer therapy. Five types of image-guided anticancer therapy using assembled AIEgens are included: chemotherapy, photodynamic therapy, photothermal therapy, gene therapy, and synergistic therapy. Moreover, a brief conclusion with the discussion of current challenges and future perspectives in this area is further presented.

A Biomimetic Aggregation-Induced Emission Photosensitizer with Antigen-Presenting and Hitchhiking Function for Lipid Droplet Targeted Photodynamic Immunotherapy

Photodynamic therapy (PDT) is a promising alternative approach for effective cancer treatment that is associated with an antitumor immune response. However, immunosuppression of the tumor microenvironment limits the immune response induced by PDT. Stimulation and proliferation of T cells is a critical step for generating immune responses and depends on the efficient presentation of tumor antigens and co-stimulatory molecules by antigen-presenting cells (APCs). Here, biomimetic aggregation-induced emission (AIE) photosensitizers with antigen-presenting and hitchhiking abilities (DC@AIEdots) are developed by coating dendritic cell (DC) membranes on the nanoaggregates of the AIEgens. Notably, the inner AIE molecules can selectively accumulate in lipid droplets of tumor cells, and the outer cell membrane can facilitate the hitchhiking of DC@AIEdots onto the endogenous T cells and enhance the tumor delivery efficiency by about 1.6 times. Furthermore, DC@AIEdots can stimulate the in vivo proliferation and activation of T cells and trigger the immune system. The potential applications of therapeutic agents targeting lipid droplets for immunotherapy are indicated and a new hitchhiking approach for drug delivery is provided. Lastly, the study presents a photoactive and artificial antigen-presenting platform for effective T cell stimulation and cancer photodynamic immunotherapy.

AIE material for photodynamic therapy

Photodynamic therapy (PDT) is emerging as an excellent strategy to treat different types of cancers. The advantages of using PDT over other cancer treatment modalities are owing to its non-invasive nature, spatiotemporal precession, controllable photoactivity, and least side effects. The photosensitization ability of traditional photosensitizers (PSs) are severely curtailed by aggregation-induced quenching (ACQ). On the contrary, aggregation induced emission (AIE) molecules/fluorogens (AIEgens) show enhanced fluorescence emission and high reactive oxygen species (ROS)/singlet oxygen (¹O₂) production capability in the aggregated state. These unique characteristics of AIEgens make them potential AIE-PSs for fluorescence/luminescence image-guided combination PDT. In this chapter, we discussed the strategies that are developed to synthesize small molecule-based AIE-PSs, metal complex-based AIE-PSs, and AIE-PSs with two-photon absorbance (TPA) properties, polymer-based AIE-PSs, and nanoparticles based AIE-PSs for PDT. We have also discussed the rational design of targeting peptide conjugated AIE-PSs to selective target cancer cells over normal cells. Furthermore, recent findings on nanoparticle-based combination AIE-PSs are also discussed, where the combination AIE-PSs show synergistically improved anticancer activity and overcome the drug resistance. Finally, we shed light on the recent development, ongoing challenges, and future directions for designing better AIE-PS for PDT.

AIEgen-loaded nanofibrous membrane as photodynamic/photothermal antimicrobial surface for sunlight-triggered bioprotection

The outbreak of infectious diseases such as COVID-19 causes an urgent need for abundant personal protective equipment (PPE) which leads to a huge shortage of raw materials. Additionally, the inappropriate disposal and sterilization of PPE may result in a high risk of cross-contamination. Therefore, the exploration of antimicrobial materials possessing both microbe interception and self-decontamination effects to develop reusable and easy-to-sterilize PPE is of great importance. Herein, an aggregation-induced emission (AIE)-active luminogen-loaded nanofibrous membrane (TTVB@NM) sharing sunlight-triggered photodynamic/photothermal anti-pathogen functions are prepared using the electrospinning technique. Thanks to its porous nanostructure, TTVB@NM shows excellent interception effects toward ultrafine particles and pathogenic aerosols. Benefiting from the superior photophysical properties of the AIE-active dopants, TTVB@NM exhibits integrated properties of wide absorption in visible light range, efficient ROS generation, and moderate photothermal conversion performance. A series of antimicrobial evaluations reveal that TTVB@NM could effectively inactivate pathogenic aerosols containing bacteria (inhibition rate: >99%), fungi (~88%), and viruses (>99%) within only 10 min sunlight irradiation. This study represents a new strategy to construct reusable and easy-to-sterilize hybrid materials for potential bioprotective applications.

Tuning the emission color of a quantum emitter by using photonic local density of states

Quantum emitters characterized by their emission colors constitute important elements in the design of modern nano-optics. Although we can change the emission colors of a quantum emitter by tailoring its chemical component, once selected, the color usually cannot be changed. It will be tempting to find out whether the emission color of an emitter could be tuned without touching its chemical component. In this Letter, we theoretically propose a strategy to externally tune the emission color of a model emitter by changing its electromagnetic environment. We found that the photonic local density of states (PLDOS) strongly affect the competition between various internal radiative and nonradiative channels, thus enabling a selective electronic state to dominate the emission spectrum. Indeed, quantitative calculations show that the emission color of a model emitter could be tuned from red to green and blue as the PLDOS increases. Moreover, due to direct correspondence between the emission color and PLDOS, the emitter can be potentially used as a sensor to characterize the local electromagnetic environment by its emission color at the nanoscale. This simple strategy may prove to be useful in the future design of various nano-optical devices.

Aggregation-induced emission fluorophores based on strong electron-acceptor 2,2'-(anthracene-9,10-diylidene) dimalononitrile for biological imaging in the NIR-II window

In this communication, three novel donor-acceptor-donor type second near-infrared AIE fluorophores based on strong electron-acceptor 2,2'-(anthracene-9,10-diylidene) dimalononitrile have been successfully developed for bioimaging, in which they exhibit good photostability and can be used in mouse ear vessel imaging with high resolution (FWHM = 93.4 μm/SBR = 1.5) after capsuling in nanoparticles with good biocompatibility.

Progress and trends of photodynamic therapy: From traditional photosensitizers to AIE-based photosensitizers

Photodynamic therapy (PDT) is an established clinical treatment technology which utilizes excitation light of a specific wavelength to activate photosensitizers (PSs) to generate reactive oxygen species (ROS), which leads to cancer cell death. Over the past decades of PDT research, progress have been made in the development of PSs. However, many inherent characteristics of traditional PSs have caused various problems in PDT, such as low treatment efficiency at aggregation state and shallow treatment depth. In solution to these problems, aggregation-induced emission (AIE)-based PSs have been reported in recent years. Here, this article reviews the design strategy and the biomedical applications of AIE PSs in detail, which begins with a summary of traditional PSs for a comparison between traditional PSs and AIE PSs. Subsequently, the different functional AIE PSs in photodynamic cancer cells ablation and image-guided therapy are discussed in detail taking controllable excitation wavelength, stimulus response and PDT/photothermal therapy synergistic effect as examples. These studies have demonstrated the great potential of AIE PSs as effective theranostic agents. And the review provides references for the development of new PSs and hopefully spur research interest in AIE PSs for future clinical application.

Innovative Synthetic Procedures for Luminogens Showing Aggregation-Induced Emission

As a consequence of their intrinsic advantageous properties, luminogens that show aggregation-induced emission (AIEgens) have received increasing global interest for a wide range of applications. Whereas general synthetic methods towards AIEgens largely rely on tedious procedures and limited reaction types, various innovative synthetic methods have now emerged as complementary, and even alternative, strategies. In this Review, we systematically highlight advancements made in metal-catalyzed functionalization and metal-free-promoted pathways for the construction of AIEgens over the past five years, and briefly illustrate new perspectives in this area. The development of innovative synthetic procedures will enable the facile synthesis of AIEgens with great structural diversity for multifunctional applications.

Aggregation-Induced Emission Properties in Fully π-Conjugated Polymers, Dendrimers, and Oligomers

Aggregation-Induced Emission (AIE) in organic molecules has recently attracted the attention of the scientific community because of their potential applications in different fields. Compared to small molecules, little attention has been paid to polymers and oligomers that exhibit AIE, despite having excellent properties such as high emission efficiency in aggregate and solid states, signal amplification effect, good processability and the availability of multiple functionalization sites. In addition to these features, if the molecular structure is fully conjugated, intramolecular electronic interactions between the composing chromophores may appear, thus giving rise to a wealth of new photophysical properties. In this review, we focus on selected fully conjugated oligomers, dendrimers and polymers, and briefly summarize their synthetic routes, fluorescence properties and potential applications. An exhaustive comparison between spectroscopic results in solution and aggregates or in solid state has been collected in almost all examples, and an opinion on the future direction of the field is briefly stated.

A lipid droplet targeted fluorescent probe for high-efficiency image-guided photodynamic therapy of renal cell carcinoma

A lipid droplets (LDs) specific fluorescent probe TTIE is prepared for LDs specific image-guided photodynamic therapy (PDT), which can light up the LDs in human clear cell renal cell carcinoma cells and tissues, and kill tumor cells via PDT process.

A triphenylamine derived fluorescent probe for efficient detection of H2S based on aggregation-induced emission

The probe TPA-HS can quickly identify H₂S (20 minutes) and release TPA-CHO with aggregation-induced emission properties.

Nanomaterials with Supramolecular Assembly Based on AIE Luminogens for Theranostic Applications

One of the major pursuits of biomedical science is to develop advanced strategies for theranostics, which is expected to be an effective approach for achieving the transition from conventional medicine to precision medicine. Supramolecular assembly can serve as a powerful tool in the development of nanotheranostics with accurate imaging of tumors and real-time monitoring of the therapeutic process upon the incorporation of aggregation-induced emission (AIE) ability. AIE luminogens (AIEgens) will not only enable fluorescence imaging but will also aid in improving the efficacy of therapies. Furthermore, the fluorescent signals and therapeutic performance of these nanomaterials can be manipulated precisely owing to the reversible and stimuli-responsive characteristics of the supramolecular systems. Inspired by rapid advances in this field, recent research conducted on nanotheranostics with the AIE effect based on supramolecular assembly is summarized. Here, three representative strategies for supramolecular nanomaterials are presented as follows: a) supramolecular self-assembly of AIEgens, b) the loading of AIEgens within nanocarriers with supramolecular assembly, and c) supramolecular macrocycle-guided assembly via host-guest interactions. Meanwhile, the diverse applications of such nanomaterials in diagnostics and therapeutics have also been discussed in detail. Finally, the challenges of this field are listed in this review.

Nonconjugated Biocompatible Macromolecular Luminogens for Sensing and Removals of Fe(III) and Cu(II): DFT Studies on Selective Coordination(s) and On-Off Sensing

This work reports the design and synthesis of two nonaromatic biocompatible macromolecular luminogens, i.e., 2-(dimethylamino)ethyl methacrylate-co-2-(dimethylamino)ethyl 3-(N-(methylol)acrylamido)-2-methylpropanoate-co-N-(methylol)acrylamide/DMAEMA-co-DMAENMAMP-co-NMA (P1) and methacrylic acid-co-3-(N-(methylol)acrylamido)-2-methylpropanoic acid-co-N-(methylol)acrylamide/MEA-co-NMAMPA-co-NMA (P2), prepared through in situ anchored acrylamido-ester/DMAENMAMP and acrylamido-acid/NMAMPA third comonomers, respectively, in a facile polymerization of two non-luminous monomers in water medium to circumvent the drawbacks related to aggregation-caused quenching of aromatic luminogens. The structures of P1/P2, in situ anchored comonomers, fluorophores, N-branching associated n-π* interactions, and hydrogen bonding assisted aggregation-enhanced emissions are comprehended by nuclear magnetic resonance, Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible, thermogravimetric analysis (TGA), dynamic light scattering (DLS), transmission electron microscopy (TEM), fluorescence lifetime, and fluorescence imaging. P1 and P2 are appropriate for sensitive detections/exclusions of Fe(III)/Cu(II) and cell-imaging. The intrinsic fluorescence, on-off sensing, selective coordinations of Fe(III) and Cu(II) with fluorophores, emission quenching mechanisms, and removals of Fe(III) and Cu(II) are investigated by DFT/NTO analyses of P1/P2 and Fe(III)-P1 and Cu(II)-P2 complexes, XPS, and isotherms and kinetics parameters. The excellent biocompatibilities, comparable limit of detections, i.e., 1.70 × 10^-7 and 1.59 × 10^-7 [m], and higher adsorption capacities, i.e., 77.25 and 154.13 mg g^-1 , at low ppm; 303 K; and pH = 7 compel P1/P2 to be acceptable for multipurpose applications.