Aggregation-induced Emission Properties Research Articles

Helical self-assembly and Fe3+ detection of V-shaped AIE-active chiral tetraphenylbutadiene-based polyamides.

Chiral aggregation-induced emission (AIE) molecules have drawn attention for their helical self-assembly and special optical properties. The helical self-assembly of AIE-active chiral non-linear main-chain polymers would produced some desired optical features. In this work, a series of V-shaped chiral AIE-active polyamides P1-C3, P1-C6, P1-C12 and linear P2-C3, P2-C6, bearing n-propyl/hexyl/dodecyl side-chains, based on tetraphenyl-butadiene (TPB) were prepared. All of the target main-chain polymers exhibit distinct AIE characteristics. The polymer P1-C6 with moderate length alkyl chains shows better AIE properties. The V-shaped main-chains and the chiral induction of (1R,2R)-(+)-1,2-cyclohexanediamine in each repeatingunit promote the polymer chains display helical conformations, and multiple helical polymer chains induce nano-fibers helicity when the polymer chains aggregate and self-assemble in THF/H2O mixtures. Simultaneously, the helical conformation polymer chains and helical nano-fibers cause P1-C6 produce strong CD signals with positive Cotton effect. Moreover, P1-C6 could also occur fluorescence quenching response to Fe3+ selectively with a low detection limit of 3.48 μmol/L.

Precise Molecular Engineering of Type I Photosensitizer with Aggregation-Induced Emission for Image-Guided Photodynamic Eradication of Biofilm.

Biofilm-associated infections exert more severe and harmful attacks on human health since they can accelerate the generation and development of the antibiotic resistance of the embedded bacteria. Anti-biofilm materials and techniques that can eliminate biofilms effectively are in urgent demand. Therefore, we designed a type I photosensitizer (TTTDM) with an aggregation-induced emission (AIE) property and used F-127 to encapsulate the TTTDM into nanoparticles (F-127 AIE NPs). The NPs exhibit highly efficient ROS generation by enhancing intramolecular D-A interaction and confining molecular non-radiative transitions. Furthermore, the NPs can sufficiently penetrate the biofilm matrix and then detect and eliminate mature bacterial biofilms upon white light irradiation. This strategy holds great promise for the rapid detection and eradication of bacterial biofilms.

AIE-active dipyridinyltriphenylamine for dual-model visualization of latent fingerprints

The development of highly efficient latent fingerprints technology (LFPs) on different background remains extremely vital for forensic and criminal investigations. In this work, a pure organic molecular sensor (DPTPA1) was designed to image LFP with strong signal-to-noise ratio by optimizing the imaging technology. DPTPA1 exhibits aggregation-induced emission (AIE) properties in both aqueous solution and solid state. Two pyridine moieties and one aldehyde moiety were introduced as the end-capped units. DPTPA1 exhibits the typical solvatochromic effect whose maximum emission wavelengths red-shift from 410 nm to 540 nm with the increasing polarity of solvents. The obvious emission of DPTPA1 in the aqueous solution is observed around 500 nm (φ = 9.6%). Both cyanoacrylate glue fuming (CGF) and powder dusting (PD) methods were used to obtain the fluorescent images of LFP on glass, tinfoil, steel and plastic substrates. Among them, the CGF method can image the clear second level details of LFP on the glass and tinfoil. The PD method using DPTPA1-loaded silica gel material can obtain the high quality LFP images on the curved surface of all four substrates. This work provides a strategy for lowing the cost in the broad fields of LFPs imaging.

Surfactant regulated aggregation-induced emission of tetraphenylethene-based tetracationic salt for the construction of light harvesting supramolecular system

Fluorescence resonance energy transfer (FRET) is an efficient optical molecular scale that has been widely used in many fields, and aggregation-induced emission (AIE) luminescent materials show great potential in constructing FRET systems. In this paper, an efficient supramolecular polymer of AIE was prepared in aqueous solution based on tetraphenylethene-based tetracationic salt molecule (1) with AIE properties, using the hydrophobic effect and electrostatic interaction with sodium dodecyl sulfonate (AS). Then, based on supramolecular aggregate (1-AS) and Rhodamine B (RB) dye, the efficient FRET system was prepared in aqueous solution with 1-AS as energy donor and RB as energy acceptor. The Stokes shift of the system can reach 208 nm, and the fluorescence intensity of RB aqueous solution with the same concentration increased 11.80 times. Moreover, the energy transfer efficiency and the antenna effect value reached 77.5%, 14.3, respectively. The method based on simple AIE donor to achieve efficient luminescence of dye molecules is of great significance for the realization of efficient light-trapping system of aqueous solution in practical applications.

An AIE-Active NIR Fluorescent Probe with Good Water Solubility for the Detection of Aβ1-42 Aggregates in Alzheimer's Disease.

Alzheimer's disease (AD), an amyloid-related disease, seriously endangers the health of elderly individuals. According to current research, its main pathogenic factor is the amyloid protein, which is a kind of fibrillar aggregate formed by noncovalent self-assembly of proteins. Based on the characteristics of aggregation-induced emission (AIE), a bislactosyl-decorated tetraphenylethylene (TPE) molecule TMNL (TPE + malononitrile + lactose), bearing two malononitrile substituents, was designed and synthesized in this work. The amphiphilic TMNL could self-assemble into fluorescent organic nanoparticles (FONs) with near-infrared (NIR) fluorescence emission in physiological PBS (phosphate buffered saline), achieving excellent fluorescent enhancement (47-fold) upon its combination with Aβ1-42 fibrils. TMNL was successfully applied to image Aβ1-42 plaques in the brain tissue of AD transgenic mice, and due to the AIE properties of TMNL, no additional rinsing process was necessary. It is believed that the probe reported in this work should be useful for the sensitive detection and accurate localization mapping of Aβ1-42 aggregates related to Alzheimer's disease.

The effect of –CF3 substitution position on the aggregation-induced emission, solvatofluorochromism and mechanofluorochromism properties of the conjugated 9-butyl-9H-carbazole phenylacrylonitrile derivatives

A series of 9-butyl-9H-carbazole derivatives with intense solid-state emission were synthesised by the Knoevenagel reaction of 9-butyl-9H-carbazole-3-carbaldehyde with phenyl acetonitrile derivatives with –CF3 group at different substituent positions of the phenyl group. They exhibit remarkable aggregation-induced emission (AIE), solvatofluorochromism and mechanofluorochromic (MFC) properties depending on the –CF3 substitution site. The ortho-substituted derivative shows enhanced charge transfer properties with a distinct dual-state fluorescence emission. This peculiar property is further utilised for data encryption and anti-counterfeiting applications. The para-substituted derivative exhibits an increased solid-state fluorescence quantum yield of 88% with switchable MFC properties. The ground and excited state photophysical properties of the synthesised luminogens were explored using various spectroscopic techniques. The study provides an efficient strategy to understand the effect of the –CF3 substitution position in tuning and modifying the luminescence properties of the organic solids via subtle modifications in the molecular scaffolds.

Regulating the proximity effect of heterocycle-containing AIEgens

Proximity effect, which refers to the low-lying (n,π*) and (π,π*) states with close energy levels, usually plays a negative role in the luminescent behaviors of heterocyclic luminogens. However, no systematic study attempts to reveal and manipulate proximity effect on luminescent properties. Here, we report a series of methylquinoxaline derivatives with different electron-donating groups, which show different photophysical properties and aggregation-induced emission behaviors. Experimental results and theoretical calculation reveal the gradually changed energy levels and different coupling effects of the closely related (n,π*) and (π,π*) states, which intrinsically regulate proximity effect and aggregation-induced emission behaviors of these luminogens. With the intrinsic nature of heterocycle-containing compounds, they are utilized for sensors and information encryption with dynamic responses to acid/base stimuli. This work reveals both positive and negative impacts of proximity effect in heterocyclic aggregation-induced emission systems and provides a perspective to develop functional and responsive luminogens with aggregation-induced emission properties.

Double-Site Twisted D-π-D′ Conjugates with Versatile Photophysical Facets for Diverse Optical Applications and Wash-Free Bioimaging of Cancer Cells

It is still a conundrum to design a single but simple organic molecule possessing numerous realistic photophysical properties such as mechanofluorochromism, aggregation-induced emission (AIE) properties, solvatochromic DSE-gens (dual-state emissive fluorogens), and viscofluorochromism. Unlike D-π-A, D-π-D′ systems are seldom explored with various applied features. This work finds how a single D-π-D′ indole-anthracene conjugate displays all these properties with real-world applications. Especially, an indole-anthracene-π-phenothiazine conjugate (IAP) appears as a solvatochromic (91 nm shift) DSE-gen that shows the longest 62 nm blueshifted enhanced emission on aggregation and the longest 45 nm blueshifted viscofluorochromic features. Furthermore, IAP adopts a fingertip-pressure-sensitive 35 nm blueshift, while a triphenylamine-linked analogue IAT demonstrates a 23 nm mechanofluorochromic redshift. Conformationally twisted backbone and π-conjugations are judiciously balanced to exhibit these optical features. Such diverse and contrasting photophysical facets are elucidated through experimental and detailed time-dependent density functional theory investigations to meet rational understandings. These fluorophores are utilized as hidden patent fingerprint memory-based platforms and software-assisted comparison studies to identify counterfeiters. Furthermore, highly sensitive fingertip-aided mechanofluorochromic features are useful for inkless security writing. Besides, wash-free bioimaging of robust oral cancer cells (FaDu) could be accomplished satisfactorily in the green (IAT) and orange-red regions (IAP) with a lower probe concentration. The anticancer property of IAT enables visualization of the progressive distortion of the dying cancer cells during wash-free bioimaging.

The blue fluorescence luminescence properties of hyperbranched polysiloxane containing halogen atom

AbstractIn order to obtain a new class of aggregation‐induced emission (AIE) polymers without common conjugated chromophores in their structures, hyperbranched polysiloxanes (HBPSi) containing halogen elements were obtained by introducing chlorine and bromine atoms into HBPSi (Cl‐HBPSi, Br‐HBPSi) through one‐step polycondensation reaction. The relationship between the chemical structure and fluorescence properties of the two types of HBPSi was studied. The results show that both Cl‐HBPSi and Br‐HBPSi prepared in this study can emit bright blue light under a UV lamp of 365 nm wavelength, and appropriate ratio of raw materials can endow the halogenated HBPSi with moderate degree of polymerization, and give it strong excitation intensity and emission intensity. Meanwhile, Br‐HBPSi exhibits a higher fluorescence intensity, which is due to the ‘heavy atom effect’ of halogen atoms. In addition, for different concentrations of tetrahydrofuran (THF) solutions with the same addition of HBPSi, the luminescence intensity increases gradually with the decrease of THF concentration. These results indicate that the emission intensity is affected by the molecular weight and concentration of polymers, and that the AIE properties of halogenated HBPSi are related to the ‘impurity atomic clusters’ formed by halogenated atoms and the hydroxyl groups formed by the heterogeneity of HBPSi. © 2023 Society of Industrial Chemistry.

Dehydroabietic acid and triphenylamine combined BioAIEgens with an imine linker and RIM: mechanochromism and acidichromism

The petrochemical-based multi-stimuli responsive materials have been widely explored as advanced functional materials in the past several decades, but they inevitably face problems like complicated synthesis, non-renewability, and non-sustainability. On this basis, the bio-based materials used to construct multi-stimuli responsive due to the unique natural structures have come to the fore. In this work, three novel triphenylamine-based salicylideneanilines have been simply designed with aggregation-induced emission (AIE) properties. Among all, DAMB-TPAOH and DAMB-TPA possessing the natural structure of dehydroabietic acid from rosin are bioproduct-inspired AIE luminogens (BioAIEgens). Derived from the excited-state intramolecular proton transfer (ESIPT) and restriction of intramolecular motion (RIM) dual-mechanism caused by the hydroxyl group and rigidification of alicyclic moiety, respectively, the solid-state DAMB-TPAOH exhibits red-shifted (compared to DAMB-TPA) and stronger (compared to BA-TPAOH) emission, endowing this BioAIEgen with the best fluorescence behavior. Further, the introduction of the natural skeleton, propeller TPA, and imine group results in the high-contrast mechanochromic and acidichromic properties of DAMB-TPAOH. The multi-stimuli responsive properties endow DAMB-TPAOH with potential utilization in the manufacture of rewritable paper and multi-color ink. The current work contributes greatly to the development of BioAIEgens with both mechanochromism and acidichromism.

Stepwise Solution-Interfacial Nanoarchitectonics for Assembled Film with Full-Color and White-Light Circularly Polarized Luminescence.

The fabrication of chiral thin films with tunable circularly polarized luminescence (CPL) colors is important in developing chiroptical materials but remains challenging due to the lack of assembly-initiated chiral film formation methodology. Here, by adopting a combined solution aggregation and interfacial assembly strategy, we report the fabrication of chiral film materials with full-color and white-light CPL. A biquinoline glutamic acid ester (abbreviated as BQGE) shows a typical aggregation-induced emission property with blue CPL after solution aggregation. Subsequent interfacial assembly of these solution aggregates on a solid substrate leads to the formation of a CPL active film consisting of nanobelt structures. Since the BQGE molecule has a coordination site, the CPL emission of an individual BQGE film can be extended from blue to green emission upon coordination with a zinc ion, accompanied by morphology transition from nanobelts to nanofibers. Further extension to red-color CPL is successfully achieved by coassembly with an achiral acceptor dye. Interestingly, the proper combination of coordination ratio and acceptor loading ratio provides bright white-light CPL emission from the BQGE/Zn2+/PDA triad composite film. This work provides a new approach to fabricating chiroptical film materials with controlled microscopic morphology and tunable CPL properties.

Synthesis and aggregation-induced emission properties of α-perimidinyl 3-pyrrolyl BODIPY

A new dye called the [Formula: see text]-perimidinyl 3-pyrrolyl BODIPY(PPyBODIPY) was synthesized readily by treating [Formula: see text]-formyl 3-pyrrolyl BODIPY with 1,8-diamino naphthalene in ethanol at reflux. The PPyBODIPY was thoroughly characterized and studied by HR-MS, 1D & 2D NMR, absorption, fluorescence and DFT/TDDFT techniques. The PPyBODIPY absorbs strongly in the 500-600 nm region and emits weakly in the region of 550–650 nm with low quantum yield. DFT optimized structure of PPyBODIPY revealed that the 3-pyrrolyl BODIPY unit was almost planar and the perimidinyl moiety was oriented at 78.88[Formula: see text] relative to appended pyrrole of 3-pyrrolyl BODIPY unit. The photophysical studies revealed that the PPyBODIPY acts as AIEgen and showed aggregation-induced emission behavior in a 60% H2O-THF mixture.

Development of meso-Five-Membered Heterocycle BODIPY-Based AIE Fluorescent Probes for Dual-Organelle Viscosity Imaging.

Fluorescent rotors with aggregation-induced emission (AIE) and organelle-targeting properties have attracted great attention for sensing subcellular viscosity changes, which could help understand the relationships of abnormal fluctuations with many associated diseases. Despite the numerous efforts spent, it remains rare and urgent to explore the dual-organelle targeting probes and their structural relationships with viscosity-responsive and AIE properties. Therefore, in this work, we reported four meso-five-membered heterocycle-substituted BODIPY-based fluorescent probes, explored their viscosity-responsive and AIE properties, and further investigated their subcellular localization and viscosity-sensing applications in living cells. Interestingly, the meso-thiazole probe 1 showed both good viscosity-responsive and AIE (in pure water) properties and could successfully target both mitochondria and lysosomes, further imaging cellular viscosity changes by treating lipopolysaccharide and nystatin, attributing to the free rotation and potential dual-organelle targeting ability of the meso-thiazole group. The meso-benzothiophene probe 3 with a saturated sulfur only showed good viscosity-responsive properties in living cells with the aggregation-caused quenching effect and no subcellular localization. The meso-imidazole probe 2 showed the AIE phenomenon without an obvious viscosity-responsive property with a C═N bond, while the meso-benzopyrrole probe 4 displayed fluorescence quenching in polar solvents. Therefore, for the first time, we investigated the structure-property relationships of four meso-five-membered heterocycle-substituted BODIPY-based fluorescent rotors with viscosity-responsive and AIE properties, and among these, 1 with a C═N bond and a saturated sulfur on the meso-thiazole, potentially contributing to their corresponding AIE and viscosity-responsive properties, served as a sensitive AIE fluorescent rotor for imaging dual-organelle viscosity in both mitochondria and lysosomes.

An interesting fluorescent probe with aggregation-induced emission for highly sensitive and selective detection of Hg2+

The development of highly sensitive analytical methods for detection of trace level of mercury (II) has always arouse great interests owing to its notoriously toxicity to natural environment and human health. In this paper, an interesting “turn-on” fluorescent probe L for detection of Hg2+ based on 2-hydroxy-1-naphthaldehyde derivative was synthesized, and its chemical structure was confirmed by IR, 1H NMR, 13C NMR, ESI-MS and single crystal. Probe L exhibits aggregation-induced emission properties and provides a simple and efficient strategy for highly selective and sensitive detection of Hg2+ in an aqueous solution of DMSO/H2O (1:4, v:v). According to job curve and fluorescence titration, probe L with Hg2+ forms a 1:1 ratio of complex, and its lowest detection limit is 6.35×10−9 mol/L. Probe L toward detection of Hg2+ presents significant advantages such as low-cost, structural stability, high water solubility, rapid response and allowing their long-term use. The potent applicants for probe L were also investigated and indicated it could conveniently be made a series of sensor strips and applied to rapidly detect trace Hg2+ in traditional Chinese medicine.

Unraveling the Mechanism of ACQ-to-AIE Transformation of Fluorescein Derivatives.

Although fluorescein derivatives have excellent properties and strong practicability, they are typical aggregation-induced quenching (ACQ) molecules, which are not conducive to working in the solid state. Recently, the fluorescein derivative Fl-Me with aggregation-induced emission (AIE) property was synthesized, which brought a new dawn for the research and development of fluorescein-based materials. In this study, the AIE mechanism of Fl-Me was investigated based on time-dependent density functional theory and the ONIOM method. The results revealed that an effective dark-state deactivation pathway leads to the fluorescence quenching of Fl-Me in a solution environment. Accordingly, the AIE phenomenon originates from the closure of the dark-state quenching channel. It is worth emphasizing that we found that the carbonyl group of molecular Fl-Me has intermolecular hydrogen bonding interaction with the adjacent molecules, which caused the increase of the dark-state energy in the crystalline state. Moreover, the restriction of the rotational motion and the nonexistence of the π-π stacking interaction are beneficial to the enhancement of fluorescence upon aggregation. Finally, the ACQ-to-AIE transformation mechanisms of fluorescein derivatives have been discussed. This work provides deeper insight into the photophysical mechanism for the fluorescein derivatives Fl-Me with AIE feature and eventually is expected to help researchers to develop more fluorescein-based AIE materials with remarkable properties for various fields.

Cyano and Isocyano-substituted Tetraphenylethylene with AIE Behavior and Mechanoresponsive Behavior

Dual-functional materials with AIE behavior and mechanoresponsive behavior have attracted considerable attention due to their promising applications in mechano-sensors, optical storage, solid-state optoelectric devices and bioimage systems. AIEgens bearing tetraphenylethylene (TPE) core become elementary building blocks in many fluorescent functional materials. In this article, cyano-and isocyano-electronic withdrawing groups are incorporated with TPE skeleton to form tetracyanophenylethylene (TPE-CN) and tetraisocyanophenylethylene (TPE-NC). Their structures are confirmed by NMR, Mass Spectra and single crystal X-ray measurement. These two isomers reflect aggregation-induced emission (AIE) property in solution state and mechanochromic behavior in solid state. Interestingly, their luminescent intensities, quantum yields and fluorescent lifetime in solid state have an obvious increase upon grinding. The theoretical calculation of these two compounds clarify their difference in optical properties. The mechanochromic mechanism is also intensively explained by powder X-ray measurements.

Visible light-triggered acceptor-acceptor type dithienylethene with aggregation-induced emission for NIR photochromism in aqueous media

Photochromic dithienylethene (DTE) derivatives with aggregation-induced emission (AIE) performance are appealing for photoelectric functional materials and photopharmacology. However, they often have to be triggered by ultraviolet light to induce photoisomerization, severely limiting their potential applications in biological systems. Herein, a novel acceptor (A)-acceptor (A) type DTE derivative (CNSDTE) has been rationally designed and prepared, in which the cyanostilbene moieties as strong electron-withdrawing groups are incorporated into both sides of DTE skeleton. Its chemical structure is fully verified by 1H NMR, 13C NMR and HRMS. Upon alternating irradiation of visible and near-infrared light, CNSDTE shows excellent photochromic properties in toluene, chloroform and DMSO. Before irradiation with visible light, AIE properties and solid state luminescence behavior are observed. Furthermore, CNSDTE-loaded nanoparticles (CNSDTE NPs) are facilely fabricated by taking the amphiphilic Pluronic F127 as the encapsulating matrix. The as-prepared CNSDTE NPs display excellent photoswitching behavior in aqueous media. The experimental results of the excellent AIE properties and photoswitching behaviors in the various media is also confirmed by DFT calculations. In short, it may be employed in functional biomaterials as a novel visible light-triggered fluorescence switch with AIE features.

Turning enol* emission of SBOH via restricting twisted intramolecular charge transfer behavior by pressure.

Stimuli-responsive luminogens with aggregation-induced emission and excited state intramolecular proton transfer (ESIPT) properties have applications in storage devices, anti-counterfeiting, imaging, and sensors. Nevertheless, group rotation appears in twisted intramolecular charge transfer (TICT) state, resulting in decreased fluorescence intensity. Inhibiting TICT remains a challenge based on their intrinsic molecular configuration. Herein, we present a simple facile pressure-induced method to restrict the TICT behavior. Steady-state spectroscopy measurement shows that fluorescence enhancement and color shifts can be achieved under high pressure. Combined with in situ high-pressure ultrafast spectroscopy and theoretical calculations, the TICT behavior was restricted in two aspects. The ESIPT process was damaged, hence more particles stored in the E* state, and transferred to the TICT state hardly. Also, the rotation of (E)-dimethyl5-((4-(diethylamino)-2-hydroxybenzylidene)amino)isophthalate (SBOH) was restricted, significantly increasing the fluorescence intensity. This approach provides a new strategy for the development of stimulus-responsive materials.

Aggregation-induced emission near-infrared photosensitizer with time-responsive dual-organelles targeting for accelerating cancer cells apoptosis and metastasis inhibition

Photodynamic therapy (PDT) combined with critical organelle targeting can maximize ablation of malignant tumors, which is a desirable route against cancer. However, the short excitation/emission wavelengths of conventional photosensitizers (PSs), the inefficient production of reactive oxygen species (ROS) and the inevitable aggregation-induced quenching phenomenon have restricted their development. Herein, we developed and synthesized a set of photoactivated fluorescent probes named MoTQu and MeTQu with aggregation-induced emission properties. The both of fluorescent probes have merits of bright near-infrared fluorescence emission, large stokes shift and enhanced intramolecular charge transfer attributed to the synergistic interaction of strong donor and acceptor of molecular. In addition, the optimal PS named MoTQu not only possesses superior anti-photobleaching, biocompatibility and extremely high-level ROS generation efficiency, on the other hand, can time-responsive target mitochondria and lysosomes in living cells to cause lysosomal dysfunction by generating large amount of ROS in situ under photoexcitation, subsequently targeting mitochondria through the positive electrical properties of the quinoline fraction, further inducing and promoting cancer cell damage and irreversible apoptosis. Consequently, we are convinced that MoTQu can be a powerful tool to foster the development of image-guided PDT.

Highly selective discriminating E, E/E, Z isomers of functionalized 1-phenyl-2,5-divinyl-1H-pyrrole for n-/sec-/tert-butyl amines and as temperature sensor

A series of novel E, E/E, Z isomers based on 5-(2-cyano-3-ethoxy-3-oxoprop-1-en-1-yl)-1H-pyrrol-2-yl acrylic acid have been successfully synthesized. The comparative studies between compounds presenting E, E/E, Z isomers on the properties of emission and effects of temperature had been discussed. Interestingly, the E, Z, and E, E isomers emitted different luminous colors and aggregation-induced emission (AIE) properties. Notably, the E, Z-OC2H5COOH and E, E-OC2H5COOH loaded on filter paper could identify alkaline compounds. Furthermore, E, E-OC2H5COOH strips could selectively discriminate for n-/sec-/tert-butylamine by changing the color of the fluorescence. In addition, E, E-OC2H5COOH, doped into polymer dimethyl silicone (PDMS) film could exhibit an evident change in emission color from orange to yellow at 90 °C and gradually vanished at 190 °C, while that of E, Z-OC2H5COOH didn't change significantly with heating. Therefore, the configuration of two double bonds can be used to regulate the change of fluorescence, improve the chemical and physical properties of materials, and break through the deficiency of single configuration regulation.