Aggregation-induced Emission Properties Research Articles

Synthesis, structure, photophysical property, stability of tetraphenylethylene-based boranil, and applications in cell imaging

A new family of tetraphenylethylene-based N,O-chelated boranil complexes (TPE-BAs) with aggregation-induced emission (AIE) characteristics were developed. X-ray crystallographic analysis indicated that the terminal substituents on the aniline moiety significantly affected the intermolecular stacking mode, thereby influencing the photophysical properties. The stabilities of these compounds are closely related to the substituents on the aniline moiety. Electron-donor-substituted TPE-BA-OMe exhibited the best stability, whereas the electron-acceptor-substituted compounds exhibited poor stability. Benefitting from its AIE properties and suitable lipophilicity, TPE-BA-OMe served as an excellent fluorescent probe for the specific bioimaging of lipid droplets in living cells.

Fluorescence-Quenching Lateral Flow Immunoassay for "Turn-On" and Sensitive Detection of Anti-SARS-Cov-2 Neutralizing Antibodies in Human Serum.

The titer of anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) neutralizing antibodies (NAbs) in the human body is an essential reference for evaluating the acquired protective immunity and resistance to SARS-CoV-2 infection. In this study, a fluorescence-quenching lateral flow immunoassay (FQ-LFIA) is established for quantitative detection of anti-SARS-CoV-2 NAbs in the sera of individuals who are vaccinated or infected within 10min. The ultrabright aggregation-induced emission properties encapsulated in nanoparticles, AIE490 NP, are applied in the established FQ-LFIA with gold nanoparticles to achieve a fluorescence "turn-on" competitive immunoassay. Under optimized conditions, the FQ-LFIA quantitatively detected 103 positive and 50 negative human serum samples with a limit of detection (LoD) of 1.29IUmL-1 . A strong correlation is present with the conventional pseudovirus-based virus neutralization test (R2 =0.9796, P<0.0001). In contrast, the traditional LFIA with a "turn-off" mode can only achieve a LoD of 11.06IUmL-1 . The FQ-LFIA showed excellent sensitivity to anti-SARS-CoV-2 NAbs. The intra- and inter-assay precisions of the established method are below 15%. The established FQ-LFIA has promising potential as a rapid and quantitative method for detecting anti-SARS-CoV-2 NAbs. FQ-LFIA can also be used to detect various biomarkers.

Sensitive Detection of Trace Explosives by a Self-Assembled Monolayer Sensor.

Fluorescence probe technology holds great promise in the application of trace explosive detection due to its high sensitivity, fast response speed, good selectivity, and low cost. In this work, a designed approach has been employed to prepare the TPE-PA-8 molecule, utilizing the classic aggregation-induced emission (AIE) property of 1,1,2,2-tetraphenylethene (TPE), for the development of self-assembled monolayers (SAMs) targeting the detection of trace nitroaromatic compound (NAC) explosives. The phosphoric acid acts as an anchoring unit, connecting to TPE through an alkyl chain of eight molecules, which has been found to play a crucial role in promoting the aggregation of TPE luminogens, leading to the enhanced light-emission property and sensing performance of SAMs. The SAMs assembled on Al2O3-deposited fiber film exhibit remarkable detection performances, with detection limits of 0.68 ppm, 1.68 ppm, and 2.5 ppm for trinitrotoluene, dinitrotoluene, and nitrobenzene, respectively. This work provides a candidate for the design and fabrication of flexible sensors possessing the high-performance and user-friendly detection of trace NACs.

Investigation of Mechanochromic Luminescence of Pyrene-based Aggregation-Induced Emission Luminogens: Correlation between Molecular Packing and Luminescence Behavior.

To better understand the correlation between molecular structure and optical properties such as aggregation-induced emission (AIE) and mechanochromic luminescence (MCL) emission, two new pyrene-based derivatives with substitutions at the 4- and 5-positions (1HH) and at the 4-, 5-, 9-, and 10-positions (2HH) were designed and synthesized. Cyano groups were introduced at the periphery of the synthesized compounds (1HCN, 1OCN, 1BCN, 2HCN, 2OCN, and 2BCN) to investigate the influence of these groups on the emission properties of the pyrene derivatives both in solution and in the solid state. The fluorescence emission performance of these compounds in water/acetone mixtures was simultaneously studied, revealing outstanding aggregation-induced emission properties. The typical shift in emission maxima to higher values was attributed to J-aggregate formation in the aggregate state. Careful investigation of the crystal structures demonstrated abundant and intense intermolecular interactions, such as C-H…π and C-H…N hydrogen bonds, contributing to the remarkable mechanochromic luminescence performance of these compounds. The MCL properties of all the compounds were investigated using powder X-ray diffraction, and the remarkable mechanochromic properties were attributed to J-aggregate phenomena in the solid state. These results provide valuable insights into the structure-property relationship of organic MCL materials, guiding the design of efficient organic MCL materials.

The inherent AIE feature revealed the drug molecular state in cyclodextrin metal–organic framework for enhanced stability and absorption

The amorphous form of a drug can greatly improve the solubility and rates of dissolution for enhancing oral bioavailability. However, amorphous drugs tend to crystallize thus negating their solubility advantages. Here, we use a nanoconfinement strategy to prevent the crystallization of amorphous solids by loading the poorly soluble drug indomethacin (IMC) into a porous γ-cyclodextrin-based metal–organic framework (CD-MOF). The inherent aggregation-induced emission (AIE) property of IMC was successfully applied as a sensitive fluorescence imaging tool to visualize its molecular state in the solid form. A distinct high-energy, non-aggregated molecular state of IMC in CD-MOF was revealed by the AIE turn-off phenomenon together with other solid-state characterization methods. The IMC@CD-MOF exhibited excellent physical stability even when stored at high temperature or humidity. The high supersaturated drug solutions were immediately generated and maintained during the dissolution of IMC@CD-MOF, resulting in a great enhancement of in vivo bioavailability. The inherent AIE feature of drugs can facilitate the understanding of the structure–property relationship in complex delivery systems, which is essential for the design and optimization of drug carriers with desired stability and biopharmaceutical performance.

Synthesis of highly substituted alkenes by sulfur-mediated olefination of N-tosylhydrazones

Tetraphenylethylenes (TPEs) are well-known for their aggregation-induced emission properties. The synthesis of TPE derivatives, as well as other highly substituted olefins, generally requires the use of hazardous reagents, such as metalorganic compounds, to overcome the high activation energies caused by the sterically congested double bond. Herein, we present an efficient and metal-free procedure for the synthesis of tetraarylethylenes via alkylidene-homocoupling of N-tosylhydrazones, derived from readily available benzophenones, in excellent yields. The method relies only on cheap and benign additives, i.e. elemental sulfur and potassium carbonate, and easily competes with other established procedures in terms of scope, yield and practicability. A mechanistic study revealed a diazo compound, a thioketone and a thiirane as key intermediates in the pathway of the reaction. Based on this, a modified method, which allows for selective alkylidene-cross-coupling, generating a broader scope of tri- and tetrasubstituted olefins in good yields, is showcased as well.

Fine-tuning bromide AIE probes for Hg2+ detection in mitochondria with wash-free staining

Mercury ions (Hg2+) primarily target mitochondria in the cells. Therefore, the development of novel probes that specifically target mitochondria in the presence of Hg2+ is of immense importance. Most previously reported probes that utilize the softness of S, Te, O, and/or N atoms for Hg2+ binding often face problems such as fluorescence quenching and off-target signals. In this study, bromide-hydrocarbon pyridinium salts were designed to target the mitochondria and chelate Hg2+ via Hg–Br coordination bonds. As a prototype, four aggregation-induced emission (AIE) fluorogens, namely TPP-Br, TPP-Cl, R1, and R2, with a similar D-π-A structure but slight differences in their halogen substituents, were designed. Among them, only TPP-Br achieved the highly selective and sensitive detection of Hg2+ by triggering its AIE properties, resulting in remarkable emission enhancement (80-fold), colorimetry, and the Tyndall effect. TPP-Br exhibited high selectivity and sensitivity to Hg2+ with a detection limit of 0.35 μM, rapid response time (<10 s), and large Stokes shift of 185 nm. Their interaction modes were studied using a combination of 1H nuclear magnetic resonance spectroscopy, scanning electron microscopy, fluorescent lifetime decay, and theoretical calculations. TPP-Br exhibited a low emission background in cells, whereas in the presence of Hg2+, mitochondria were lit up with wash-free staining. This study provides a powerful tool for accurately diagnosing mercury poisoning–related diseases in mitochondria.

Synthesis of D−A based violet−red light emitting indolo[2,3-b]quinoxalin-2-yl(phenyl)methanone amine dyes: Opto-electrochemical, AIE, and theoretical properties

In this work, we have designed and synthesized seven new amine derivatives of indolo[2,3-b]quinoxalin-2-yl(phenyl)methanone through the use of palladium-catalyzed Buchwald−Hartwig (C−N) coupling amination reaction and characterized by spectroscopic methods. Molecules offers intramolecular charge transfer (ICT) transitions, which result in absorption spectra with longer wavelengths (λmax = 385−509 nm), resembling a donor−acceptor (D−A) assembly. Consequently, the dyes emit light in violet–red region (λemi = 406−637 nm) in solution and solid film. Moreover, dye 5 and 6 demonstrate aggregation–induced emission (AIE) in THF−Water system due to the formation of nanoaggregates. Electrochemical properties investigated using cyclic voltammetry. The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were determined within the range from −4.91 to −5.76 eV and −3.03 to −3.45 eV, respectively, and comparable with reported ambipolar materials. Theoretical studies also conducted using density functional theory (DFT) and time–dependent density functional theory (TD–DFT) calculations, which agreeing with experimental data. The small energy difference between singlet (S1) and triplet (T1) states (∆EST = 0.24−0.45 eV) suggests that these dyes possess thermally activated delayed fluorescence (TADF) emitting properties. Thus, dyes propose their potential application in optoelectronic devices.

Simple Donor-π-Acceptor Compounds Exhibiting Aggregation-Induced Emission as Hidden Fingerprints Detecting Agents.

Latent fingerprints are a significant carrier of information for a court expert. To detect this type of forensic trace, what is necessary is a method that is easy to use, compact, and versatile. The research aimed to investigate the physicochemical properties of luminescent substances of donor-π-acceptor systems in terms of their potential use in detecting hidden fingerprints. During the research, a group of fluorene compounds consisting of the (-CH=C(CN)(COOR)) moiety was designed and successfully synthesized. The optical, electrochemical, and aggregation-induced emission properties were studied. The aggregation-induced emission of compounds has been studied in the mixture of THF (as a good solvent) and water (as a poor solvent) with different water fractions ranging from 0% to 99%. Due to the molecular structure, substances showed different affinities to organic traces. As a result, it was noticed that all compounds showed the AIE phenomenon, while during tests on latent fingerprints, it was observed that two substances had particularly forward-looking features in this field.

Controllable fluorescent switch based on ferrocene derivatives with AIE-active tetraphenylethene moiety

Stimuli-responsive supramolecular materials have attracted much attention because of their controllable microstructure and luminescence behavior. In this study, the fluorescent molecule ((1E)-1-((4-(1,2,2-triphenylvinyl)benzylidene)hydrazineylide-ne)ethyl)ferrocene (FcMe-TPE) with aggregation-induced emission (AIE) property and redox activity was synthesized. The morphology as well as fluorescence behavior could be modulated by changing solvent, adding oxidant or applying voltage, and the translation mechanism was explored in detail by means of density functional theory (DFT). Based on the presence of competitive hydrogen bonding, FcMe-TPE assemblies showed different aggregate behaviors and properties under different water contents (fw). As fw increased from 20% to 60%, the morphology of assemblies could be transformed from 2D sheet to elliptical crystal structure, then the precipitation gradually disappeared for the further increase of fw. At the same time, the addition of oxidant as well as the application of voltage could also cause changes in the fluorescence intensity of the assemblies. When the voltage increased from 0 V to 3 V, the fluorescence intensity increased and reached the maximum value at 1 V. Based on this property, the electrofluorochromic (EFC) device with low trigger voltage was made. This work provides a feasible strategy for controllable self-assembly and the fabrication of multiple fluorescence switches, which has potential practical application in the field of advanced anti-counterfeiting, intelligent display and information encryption.

A triphenylamine-based near-infrared fluorescence turn off probe for nitroreductase imaging

Nitroreductase (NTR) is an essential biomarker for various diseases and widely used to evaluate the hypoxia status in tumor cells. In this work, we developed a near-infrared (NIR) fluorescence “on-off” probe PTP based on a triphenylamine scaffold, with an intrinsic long wavelength emission more than 700 nm. This probe showed typical aggregation-induced emission (AIE) properties with the increase of PBS fraction (fw), which might be attributed to the restriction of intramolecular motions (RIM) effect in high aqueous solution. The frontiers molecular orbitals (FMO) of the probe PTP and the resulting reduction compounds (PT-OH and TPA-OH) were calculated to determine their structure differences. The two nitro groups were reduced in response to NTR and then released the substance TPA-OH through the 1,6-rearrangement-elimination, resulting in simultaneous fluorescence decrease. This process was also demonstrated by the DFT/TD-DFT and docking calculations, indicating a favorable structural and spatial match between the probe and NTR. More importantly, the probe was successfully used to visualize the NTR distribution in living A431 cells with nontoxicity. It exhibited a time-dependent fluorescence quenching behavior at the cellular level, making it of great potential in NTR detection for other biosystems.

Integrating Aggregation Induced Emission and Twisted Intramolecular Charge Transfer via Molecular Engineering

AbstractThe pursuit of sensitive fluorescent chromophores with integrated aggregation‐induced emission (AIE) and twisted intramolecular charge transfer (TICT) properties are attractive due to the tunable emission properties and increased intensity. However, this type of chromophore has yet to be exemplified mechanistically. In this study, a strategy is presented for manipulating the formation of TICT and the AIE effect through molecular engineering. The feasibility of TICT properties is validated by theoretical calculations and ultrafast spectroscopies. By precisely adjusting the hydrophobicity of the donor group, the fluorescence is significantly enhanced through the addition of poor solvent. These findings not only provide mechanistic elucidation for chromophores exhibiting integrated TICT and AIE properties in various environmental conditions but also underscore the critical factors for the systematic design of chromophores with high tunability and strong emissions.

Substituent-Controlled Photophysical Responses in Dihydropyridine Derivatives and Their Application in the Detection of Volatile Organic Contaminants.

In the ever-expanding realm of organic fluorophores, structurally simple and synthetically straightforward molecules with unique photophysical properties have received special attention. Among these, 1,4-dihydropyridine (DHP) is an important scaffold that permits fine-tuning of their photophysical properties through substituents on the periphery. Herein, we describe a series of solid-emissive N-substituted 2,6-dimethyl-4-methylene-1,4-dihydropyridine derivatives appended with electron-withdrawing substituents (dicyanomethylene or 2-dicyanomethylene-3-cyano-2,5-dihydrofuran) at the C-4 position and alkyl or alkylaryl groups on the DHP nitrogen. Electronic and steric tuning exerted by these substituents resulted in interesting photophysical properties such as negative solvatochromism, solidstate, and aggregation-induced emission (AIE). Theoretical calculations were carried out to explain the solvatochromic properties. Insight into the AIE properties was obtained through variable-temperature nuclear magnetic resonance and viscosity- and temperature-dependent emission studies. The variations in molecular packing in the crystal lattice with changes in the N-substituents contributed to the tuning of solid state emission properties. Detection of aromatic volatile organic compounds (VOCs) was achieved using the aggregates of the DHP derivatives. Among the VOCs, p-xylene elicited a significant enhancement in emission, allowing its detection at submicromolar levels.

Aroyl-S,N-Ketene Acetals: Luminous Renaissance of a Class of Heterocyclic Compounds.

Aroyl-S,N-ketene acetals represent a peculiar class of heterocyclic merocyanines, compounds bearing pronounced and rather short dipoles with great push-pull characteristics that define their rich properties. They are accessible via a wide array of synthetic concepts and procedures, ranging from addition-elimination and condensation procedures up to rearrangement and metal-mediated reactions. With our work from 2020, aroyl-S,N-ketene acetals have been identified as powerful and promising dyes with pronounced and vastly tunable solid-state emission and aggregation-induced emission properties. One characteristic trademark of this class of dye molecules is the level of control that could be exerted and which was thoroughly explored. Based on these results, the field was opened to extend the system to bi- and multichromophoric systems by the full toolkit of synthetic organic chemistry thus giving access to even more exciting properties and manifolded substance libraries capitalizing on the AIE properties. This review aims at outlining the reaction-based principles that allow for a swift and facile access to aroyl-S,N-ketene acetals, their methodological and structural evolution and the plethora of fluorescence and aggregation properties.

Design, synthesis, and properties of a novel red asymmetric luminescent material incorporating diphenylfumaronitrile, carbazole and acridine units

Herein, a deep red luminescent material BCZ-DBFN-AD containing asymmetric structure with both aggregation-induced emission (AIE) and hot exciton properties has been designed and synthesized through bilateral substitution molecular design strategy by introducing 9,9-dimethyl-9,10-dihydroacridine and carbazole electron donors with rotor effect on both sides of diphenylfumanitrile. The distorted molecular configuration and the introduction of larger rigid electron donors endow BCZ-DBFN-AD obvious AIE properties and high solid-state photoluminescence quantum yield (PLQY). Additionally, the distorted molecular configuration can also reduce the carrier injection barrier, activate the conversion channel from triplet exciton to singlet exciton, effectively take into account the locally excited (LE) state component and charge transfer (CT) state component in the hybrid excited state, and effectively improve the efficiency of the device. The PLQY of BCZ-DBFN-AD in the amorphous thin film is 31 %, and the maximum emission wavelength of the non-doped OLED prepared based on BCZ-DBFN-AD is 672 nm with Commission Internationale de L'Eclairage (CIE) coordinates of (0.64, 0.34). The Lmax, CEmax, PEmax, EQEmax are 2489 cd m−2, 1.01 cd A−1, 0.82 lm W−1, 1.83 %, respectively, the efficiency roll-off is only 3 %, and the exciton utilization rate is 29 %, which exceeds the upper limit of 25 % of traditional fluorescent materials.

Kilogram-scale synthesis of carbon dots with high-efficiency full-color solid-state fluorescence using an aggregation-induced emission strategy

Carbon dots (CDs), one of the most promising luminescent nanomaterials, have attracted widespread concern due to their unique optoelectronic properties and widespread application. However, mass production of solid-state CDs with highly efficient full-color emission has rarely been reported, severely limiting their practical application in solid-state lighting and displays. Here, using an aggregation-induced emission (AIE) strategy, full-color solid-state fluorescent (SSF) CDs with quantum yields (QYs) of up to 55.3–27.9% have been prepared on a kilogram scale through one-step microwave-assisted pyrolysis of the same precursors. Detailed structure–property studies demonstrate that the SSF of CDs is derived from the suppression of surface carboxyl group motions and the decrease of the non-radiative rate in their aggregated state, and that their tunable emission is attributed to the excessive fluorescence resonance energy transfer (FRET) induced by the increasing number of aromatic rings on CD surfaces. Therefore, these CDs exhibit both the AIE enhancement and red shift throughout the entire visible spectrum in the solid state. Finally, because of their excellent AIE properties, these highly efficient SSF CDs have been applied to pattern encryption, large-area luminescent fibrous membranes (LFMs), light-emitting diodes (LEDs), and fingerprint detection.

Synthesis, Structures, and Aggregation-Induced Emission Properties of Distyrylbenzene Derivatives Containing Fluorine Groups.

Distyrylbenzene derivatives with substituents on the vinylene moieties have been studied due to interest in their optoelectronic properties. In this study, we focused on distyrylbenzene derivatives with monofluoroolefin structures, expecting intermolecular H-F interactions in the solid state. UV-vis and fluorescence spectra of the obtained compounds were measured and compared with those of unsubstituted distyrylbenzene. The crystal structures of each compound were determined by single crystal X-ray diffraction and Hirshfeld surface analysis to understand the intermolecular contacts.

More Is Better: Dual-Acceptor Engineering for Constructing Second Near-Infrared Aggregation-Induced Emission Luminogens to Boost Multimodal Phototheranostics.

The manipulation of electron donor/acceptor (D/A) shows an endless impetus for innovating optical materials. Currently, there is booming development in electron donor design, while research on electron acceptor engineering has received limited attention. Inspired by the philosophical idea of "more is different", two systems with D'-D-A-D-D' (1A system) and D'-D-A-A-D-D' (2A system) structures based on acceptor engineering were designed and studied. It was demonstrated that the 1A system presented a weak aggregation-induced emission (AIE) to aggregation-caused quenching (ACQ) phenomenon, along with the increased acceptor electrophilicity and planarity. In sharp contrast, the 2A system with one more acceptor exhibited an opposite ACQ-to-AIE transformation. Interestingly, the fluorophore with a more electron-deficient A-A moiety in the 2A system displayed superior AIE activity. More importantly, all compounds in the 2A system showed significantly higher molar absorptivity (ε) in comparison to their counterparts in the 1A system. Thanks to the highest ε, near-infrared-II (NIR-II, 1000-1700 nm) emission, desirable AIE property, favorable reactive oxygen species (ROS) generation, and high photothermal conversion efficiency, a representative member of the 2A system handily performed in fluorescence-photoacoustic-photothermal multimodal imaging-guided photodynamic-photothermal collaborative therapy for efficient tumor elimination. Meanwhile, the NIR-II fluorescence imaging of blood vessels and lymph nodes in living mice was also accomplished. This study provides the first evidence that the dual-connected acceptor tactic could be a new molecular design direction for the AIE effect, resulting in high ε, aggregation-intensified NIR-II fluorescence emission, and improved ROS and heat generation capacities of phototheranostic agents.

ESIPT‐AIE Active Schiff Base Fluorescent Organic Nanoparticles Based on 2‐(2‐(4‐(4‐bromo Phenyl) Thiazol‐2‐yl)Vinyl)Phenol (BTVP) Utilized as a Multi‐Functional Fluorescent Probe

AbstractThe present study reports the synthesis and characterization of Aggregation‐Induced Emission (AIE) – Excited‐state intramolecular proton transfer (ESIPT) active 2‐(2‐(4‐(4‐bromo phenyl) thiazol‐2‐yl)vinyl)phenol (BTVP). The AIE properties of BTVP in Acetone/Water solution are investigated, and fluorescent organic nanoparticles (FONs) (sizes ranging from 150–200 nm) are prepared in various water fractions (fH2O). The established visco‐chromic property suggests that the restriction of intramolecular rotation is responsible for the AIE‐ESIPT behavior of the molecule, providing a means to sense viscosity. The synthesized FONs act as fluorescence chemosensors to detect Al3+ ions via a photoinduced electron transfer (PET) mechanism. Job's, Benesi–Hildebrand method, and 1HNMR titration confirm the 1:1 binding of BTVP with the metal ion. Studies on the emission concerning pH reveal the high stability of FONs over a broad range of pH, and a gradual change in the emission wavelength for the BTVP‐Al3+ complex (BTVP‐Al) is observed, providing a means to sense pH ranging from 2–8. The solid‐state photoluminescence of BTVP is used for latent fingerprint detection, demonstrating its efficiency in detecting both primary and secondary information. Additionally, both BTVP FNOs and BTVP‐Al are used in cell imaging, where specific nuclear staining with BTVP‐Al and cytoplasm staining with BTVP are observed.

Controlling ESIPT-based AIE effects for designing optical materials with single-component white-light emission

Aggregation-induced emission (AIE) molecules have gained significant importance in various fields such as biological imaging and organic light-emitting diodes. Here, we focused on exploring the process of the induction and control of AIE effects by modifying intramolecular hydrogen bonds. Firstly, inspired by the AIE characteristics of our reported amino-type excited-state intramolecular proton transfer (ESIPT)-based molecules, qualitative and quantitative relationships between the acidity of the amino group and the ESIPT process were investigated. They were successfully revealed through artificial intelligence modeling and quantum chemical calculations. Based on this, eight compounds, (2-(2′-aminophenyl) benzothiazole (1) and its derivatives), were synthesized. Then, their mechanism of structural and optical phenomena (AIE or aggregation-caused quenching (ACQ)) was further verified by quantum chemical calculations and experiments. It has been proved that multistage photochemical reactions could lead to the AIE phenomenon. Finally, the eight compounds were applied to biological imaging and white light material applications, benefiting from tunable dual-emission spectroscopic properties of amino compounds with ESIPT properties. This study provided extensive guidance on developing molecules with AIE properties and opened up new avenues for AIE-based principles, as well as single-component white-light emission optical materials.