Aggregation-induced Emission Properties Research Articles

In Situ-Grown 2D Perovskite Based on π-Conjugated Aggregation-Induced Emission Organic Spacer Boosting the Efficiency and Stability of 2D-3D Heterostructured Perovskite Solar Cells.

The two-dimensional-three-dimensional (2D-3D) heterostructured perovskite solar cells (PSCs) have drawn widespread interest, wherein the organic spacer plays a significant role in the photovoltaic performance. Herein, a novel π-conjugated organic spacer with the aggregation-induced emission (AIE) property, (Z)-2-([1,1'-biphenyl]-4-yl)-3-(5-(4-(3-aminopropoxy)phenyl)thiophen-2-yl)acrylonitrile (BPCSA-S), is designed and synthesized, which is successfully applied for the in situ construction of 2D-3D heterostructured PSCs via the two-step solution method. By virtue of the functional groups (i.e., cyano, thiophene, and amino) in BPCSA-S, the BPCSA-S organic spacer can trigger the in situ growth of 2D perovskites, which will serve as the template for the heteroepitaxial growth of 3D perovskites, thus obtaining a 2D-3D heterostructured film with high-quality and few defects. More pleasingly, benefiting from the AIE property and delocalized π-electrons in the π-conjugated BPCSA-S organic spacer, excellent photosensitization process and carrier transport can be achieved. Consequently, the resultant 2D-3D heterostructured PSCs yield a pleasing PCE of 22.07%, accompanied by mitigatory hysteresis, as well as enhanced stability. Our research shows a hopeful multifunctional organic spacer approach using the novel π-conjugated AIE organic spacer for high-performance PSCs.

Fluorescent responsive membrane based on terbium coordination polymer and carbon dots with AIE effect for rapid and visual detection of fluoroquinolone

In this study, based on aggregation-induced emission (AIE) effect and antenna effect, a novel portable fluorescent responsive membrane was constructed with red carbon dots (R-CDs) as reference signal and terbium coordination polymer (Tb-AMP CPs) as response signal for visual, instrument-free, and sensitive detection of fluoroquinolones (FQs). Specifically, the fluorescent responsive membrane (R-T membrane) was prepared by physically depositing R-CDs with AIE property and Tb-AMP CPs on the surface of polyvinylidene fluoride filter membranes at ambient temperature. In the presence of FQs, Tb3+ in the Tb-AMP CPs of the prepared membrane coordinated with the β-diketone structure of FQs, which turned on the yellow-green fluorescence through the “antenna effect”. As the concentration of FQs increased, the R-T membrane achieved a fluorescent color transition from bright pink to yellow-green. Its visual detection sensitivity for three FQs, including ciprofloxacin, difloxacin, and enrofloxacin, was 0.01 μM, and the detection limits were 7.4 nM, 7.8 nM, and 9.2 nM, respectively, by analyzing the color parameter green. In the residue analysis of FQs in real samples, the constructed membrane also exhibited remarkable anti-interference and reliability, which is of great significance for ensuring the safety of animal-derived food.

Bromine substituent position of tetraphenylethylene-based luminogens effect on enhanced AIE and reversible mechanofluorochromic properties by halogen bonding

The halogen atoms have been exploited for designing highly efficient aggregation-induced emission (AIE) materials in recent years, whereas the development of halogenated AIEgen has been greatly limited by the unclear inherent mechanism. In this paper, a series of 1,1,2,2-tetrakis (4-(phenyl ethynyl) phenyl) ethene (TPPE) derivatives with bromine (Br) substituents in different positions were synthesized and their unique photophysical behaviors based on the anti-heavy atom effect were investigated. The brominated TPPE derivatives possessed higher fluorescence quantum yield (ФF) than that of TPPE, resulting from the formation of intermolecular Br-based bonds. Single crystal analysis and theoretical calculations revealed that changing the positions of the Br substituents could induce the formation of different intermolecular interactions. The Br-based bonds efficiently restricted the intermolecular motion, in which the Br⋯Br bond made a decisive factor in determining the highly efficient fluorescence. TPPE derivatives displayed obvious mechanofluorochromic (MFC) properties. PXRD and SEM results demonstrated that the crystal-to-amorphous transition attributed to the reversibility of MFC properties. This work provides a straightforward and practical method to achieve highly efficient AIE-active materials with higher contrast MFC properties via introducing the halogen atoms.

Conformational Isomerization Effect on Singlet/Triplet Energy Consumption Process of Thermally Activated Delayed Fluorescence Molecules with Aggregation Induced Emission: A QM/MM Study.

Thermally activated delayed fluorescence (TADF) molecules with aggregation-induced emission (AIE) properties hold tremendous potential in biomedical sensing/imaging and telecommunications. In this study, a multiscale method combined with thermal vibration correlation function (TVCF) theory is used to investigate the photophysical properties of the novel TADF molecule CNPy-SPAC in toluene and crystal and amorphous states. In the crystal state, an increase in radiative rates and a decrease in nonradiative rates lead to AIE. Additionally, conformational isomerization effects result in significantly different luminescent efficiencies between the two crystal structures. Furthermore, the isomerization effect allows for the coexistence of three configurations in the amorphous state. Among them, the non-TADF quasi-axial (Qa) configuration may facilitate energy transfer to the TADF-characteristic quasi-equal/quasi-equal-H (Qe/Qe-H) configurations, enhancing AIE. Moreover, the Qa configuration enables rapid electron transport, offering the potential for self-doped devices. Our work elucidates a new mechanism for the isomerization effect in AIE-TADF molecules.

Strong Circularly Polarized Luminescence Promoted by AIE-active Chiral Co-assemblies in Liquid Crystal Polymer Films.

Recently, extensive works have focused on increasing the dissymmetry factors (glum) of various circularly polarized luminescence (CPL) materials, which is one of the most important factors for future applications of CPL. Herein, we designed a chiral co-assembled liquid crystal polymer (LCP) PTZ@R/S-PB2, which was prepared by chiral binary co-polymer (R/S-PB2) doped with achiral phenothiazine derivation dye (PTZ). For comparison, ternary co-polymerized LCP (R/S-PT) was synthesized by co-polymerizing with mesogenic monomer, chiral monomer and emissive monomer. Both PTZ@R/S-PB2 and R/S-PT showed aggregation-induced emission (AIE) properties. Interestingly, the CPL signals of both PTZ@R/S-PB2 and R/S-PT were reversed and amplified after thermal annealing treatment. The |glum| values of the co-assembled PTZ@R/S-PB2 were up to 0.13 at a 32 nm thickness, which was 5.4 times that of R/S-PT (|glum|=0.024). This is due to PTZ@R/S-PB2 could form more orderly chiral co-assembly structures. Noticeably, increasing the LCP film thickness could further improve the glum value, and the maximum glum of PTZ@R/S-PB2 could be enhanced to +0.91/-0.82 at a 220 nm thickness.

Structural tuning of coordination polymers with photoluminescent properties via temperature control

Using a two-solvent interdiffusion technique, the ligand tpatpy that possesses aggregation-induced emission (AIE) properties was coordinated to Cd2+ to construct two coordination polymers under conditions that differed only by reaction temperatures of 30 °C and 0 °C for 1 and 2, respectively. Single-crystal X-ray diffraction studies revealed the key structural differences were that the metal centers in 1 were five-coordinate, versus four-coordinate in 2. Thus, this system could be tuned by controlling the temperature during synthesis. UV-visible spectroscopy (UV-Vis), infrared spectroscopy (IR), powder X-ray diffraction (PXRD), thermogravimetry (TG), and the fluorescence of 1 and 2 are discussed to provide a comprehensive discussion of physical and electronic properties.

Excimer emission from polycyclic arenes bearing triphenylmethyl group: Solid-state fluorescence, mechanofluorochromism, aggregation-induced emission and cell imaging application

The excimer emission based on discrete π-stacked dimers of polycyclic π-systems has generated significant interest in the structure-luminescence relationship of excimers owing to their ultra-large Stokes shift. Herein, a series of excimer emissive luminogens were obtained by conjugating different polycyclic aromatic aldehydes (anthraldehyde, pyrenealdehyde and perylenealdehyde) with triphenylmethylamine. In crystalline states, all the molecules were arranged in the form of π-stacked arene dimers which were spatially isolated from each other by the bulky triphenylmethyl groups, and thus emitted bright excimer emission. The anthracene and pyrene derivatives showed fluorescence enhancement responses to grinding and the enhanced fluorescence could recover to the original state upon heating. The aggregation-induced emission (AIE) properties of them were dependent on the shapes and sizes of the polycyclic aromatic groups. The pyrene derivative showed the most excellent excimer-based AIE behavior among them. All of them were more apt to exhibit the excimer emission when formed nanoparticles with pluronic F-127 than that without pluronic F-127. Furthermore, PETP was utilized for bioimaging of living Hela cells and the high-resolution image was observed.

Dynamic emissive supramolecular polyrotaxanes with aggregation-induced emission property

The design and application of advanced functional materials based on pillar[5]arene derivatives have recently garnered significant attention in the field of supramolecular materials. Herein, we report a series of supramolecular polyrotaxanes based on different pillar[5]arene derivatives, namely Z16-18, Z20, and Z22, which are constructed through host–guest mediated quadruple hydrogen bonding interactions. Owing to the dynamic nature of these hydrogen bonding interactions, precise manipulation of host–guest chemistry enables the fabrication of both emissive and non-emissive polyrotaxanes. Notably, the emission response of polyrotaxane Z22 is solvent-dependent, making it a promising material for supramolecular applications due to its aggregation-induced emission (AIE) characteristics.

Synthesis of V-shaped Thiophene Based Rotor-Stilbene: Substituent Dependent Aggregation and Photophysical Properties.

Thiophene core V-shaped rotor-stilbene derivatives have been synthesized utilizing two-fold Heck coupling reaction. These compounds are blue emitters with moderate quantum yield in dilute solution. Rotor nature of the synthesized stilbenes supports aggregation induced emission (AIE) behaviour and they show substituent dependent emission behavior in aggregate state. In presence of donating groups (e.g., tert-butyl, methoxy, diphenylamine group) in stilbenes, they exhibit AIE property. But with the introduction of electron withdrawing group (nitro group), they shows aggregation caused quenching (ACQ) behavior. Different types of nano-aggregates formation is observed in aggregated state, which was confirmed by dynamic light scattering (DLS) and scanning electron microscopy (SEM) studies. The details photophysical (absorption, fluorescence, and lifetime), electrochemical property (cyclic voltammetry) and thermal stability have been investigated. Optimized structure, energy and electronic distribution of molecular orbitals have been studied by theoretical calculation.

An AIEgen and Iodine Double-Ornamented Platinum(II) Complex for Bimodal Imaging-Guided Chemo-Photodynamic Combination Therapy.

Real-time biodistribution monitoring and enhancing the therapeutic efficacy of platinum(II)-based anticancer drugs are urgently required to elevate their clinical performance. Herein, a tetraphenylethene derivative (TP) with aggregation-induced emission (AIE) properties and an iodine atom are selected as ligands to endow platinum (II) complex TP-Pt-I with real-time in vivo self-tracking ability by fluorescence (FL) and computerized tomography (CT) imaging, and improved anticancer efficacy by the combination of chemotherapy and photodynamic therapy. Especially, benefiting from the formation of a donor-acceptor-donor structure between the AIE photosensitizer TP and Pt-I moiety, the heavy atom effects of Pt and I, and the presence of I, TP-Pt-I displayed red-shifted absorption and emission wavelengths, enhanced ROS generation efficiency, and improved CT imaging capacity compared with the pristine TP and the control agent TP-Pt-Cl. As a result, the enhanced intratumoral accumulation of TP-Pt-I loaded nanoparticles is readily revealed by dual-modal FL and CT imaging with high contrast. Meanwhile, the TP-Pt-I nanoparticles show significantly improved tumor growth-inhibiting effects on an MCF-7 xenograft murine model by combining the chemotherapeutic effects of platinum(II) and the photodynamic effects of TP. This self-tracking therapeutic complex thus provides a new strategy for improving the therapeutic outcomes of platinum(II)-based anticancer drugs.

Synthesis, Characterization, and Properties of Sila-Annulated Phenanthrene Imides.

A series of sila-annulated phenanthrene imides were synthesized through a three-step synthetic route, which represent a hybrid class of biphenyl-based π-conjugated molecules incorporating an imide unit and silole. A comprehensive investigation of their structural, photophysical, and electronic properties was studied by experiment and theoretical calculations. Notably, sila-annulated phenanthrene imides with significant aggregation-induced emission (AIE) properties were observed.

Red-emissive quinoxaline-based BODIHY: Aggregation-induced emission and multi-responsive properties

Two new BODIHY-based AIEgens DQB1 and DQB2 including quinoxaline and benzothiazole scaffold have been synthesized and characterized. Comprehensive photophysical properties of the compounds in solution and aggregated/solid state have been investigated and fine-tuned via structural modifications. These display quite high Stokes shift (≥5991 cm−1) in solution and aggregated/solid state. Further, these derivatives display faint emission in solution (THF), while bright yellow [λem; 560 nm (DQB1)] and intense red [λem; ∼650 nm (DQB2)] in aggregated state with good quantum yield [Φf; 17.5 (DQB1) and 23.2 (DQB2)], and represent a family of dye with good AIE characteristics. Both the systems display superior solid state emission and crystallization-induced red-shifted emission. It has been shown that the compounds under study exhibit multi-responsive characteristics toward external stimuli, particularly significant color tuning in solid state due to mechanical stress and acid/base vapors. Crystal structure analyses for both DQB1 and DQB2 revealed efficient J-type aggregation and vital role of the intermolecular interactions toward AIE and multi-responsive properties.

Theoretical Investigation of Iridium Complex with Aggregation-Induced Emission Properties

The mechanism of aggregation-induced emission (AIE) for the bis(1-(2,4-difluorophenyl)-1H-pyrazole)(2-(20-hydroxyphenyl)-2-oxazoline)iridium(III) complex, denoted as Ir(dfppz)2(oz), was investigated with use DFT and the TD-DFT level of theory. The mechanism of radiationless deactivation of the triplet state was elucidated. Such a mechanism requires an additional, photophysical triplet channel of the internal conversion (IC) type, which is activated as a result of intramolecular motion deforming the structure of the oz ligand and distorting the iridium coordination sphere. Formally, the rotational movement of the oxazoline relative to the C–C bond in the oz ligand is the main active coordinate that leads to the opening of the triplet channel. The rotation of the oxazoline group and the elongation of the Ir-Nox bond cause a transition between the luminescent, low-lying triplet state with a d/π→π* characteristic (T1(eq)), and the radiationless d→d triplet state (T1(Ir)). This transition is made possible by the low energy barrier, which, based on calculations, was estimated at approximately 8.5 kcal/mol. Dimerization, or generally aggregation of the complex molecules, blocks the intramolecular movement in the ligand and is responsible for a strong increase in the energy barrier for the T1(eq)⇝T1(Ir) conversion of triplet states. Thus, the aggregation phenomenon blocks the nonradiative deactivation channel of the excited states and, consequently, contributes to directing the photophysical process toward phosphorescence. The mechanism involved in locking the nonradiative triplet path can be called restricted access to singlet–triplet crossing (RASTC).

Organotin(IV)-tetraphenylethylene acylhydrazone compounds with aggregation-induced emission property and application in anticancer therapy

Organotin (IV)-tetraphenylethylene (TPE) acylhydrazone compounds with aggregation-induced emission (AIE) property were prepared and characterized. The organotin (IV) compounds showed a conspicuous fluorescence improvement with a high absolute fluorescence quantum yield of 25.2 % (ClSnTPE) in the aggregation state, and restriction of intramolecular rotation (RIR) contributed to this AIE property. Using suitable fluorescence, confocal tests verified that these compounds could accumulate in the mitochondria of A549 cancer cells and decrease the mitochondrial membrane potential. Meanwhile, compounds could improve the intracellular reactive oxygen species (ROS) levels and inhibit the cell cycle (G1/G0 phase), then contributing to apoptosis. In addition to favorable in-vitro anti-proliferative activity (the similar to cisplatin), these compounds could also suppress A549 cancer cell migration. Above all, organotin (IV)-TPE acylhydrazone compounds show the promise as the mitochondrial targeting anticancer drugs for further study.

Two helical Schiff bases with “AIE+ESIPT” characteristics exhibiting selective ion recognition properties

Two racemic Schiff bases (H4L1 and H4L2) were synthesized and characterized, and the crystal structures indicated their helical configurations with equal amounts of P- and M-helicity. The aggregation-induced emission (AIE) and selective ion recognition properties of H4L1 and H4L2 were investigated using UV–vis absorption and fluorescence spectra. The results showed that both H4L1 and H4L2 exhibited obvious “AIE + ESIPT” characteristics in THF/H2O solution upon increasing the water fraction. Both H4L1 and H4L2 displayed an obvious turn-off fluorescence response to Cu2+ and F−, and a slight turn-off response to Fe3+ in DMSO, while they displayed an efficient selective ion recognition of Cu2+ in THF/H2O (1: 1, V/V). The corresponding stoichiometry ratio, association constant, Stern-Volmer quenching constant, and the detection limits were determined via Job's plots, UV–vis spectra titration as well as fluorescence spectra titration experiments. The crystal structures of the complexes obtained from the interactions of H4L1 with Cu2+ and Fe3+ illustrated their binding modes and binding differences, which helped us interpret the ion recognition mechanism of H4L1 and H4L2. In addition, the application of H4L2 on test strips was performed, indicating that H4L2 can be used for the rapid detection of Cu2+ and F− in THF. The acid-responsive fluorescence behavior of H4L2 showed that the white light emission can be obtained upon the addition of hydrochloric acid or aldehyde c into H4L2.

Photodynamic inactivation of Listeria monocytogenes using a natural aggregation-induced emission photosensitizer and its application in salmon preservation

Photodynamic sterilization has been regarded as a promising alternative to conventional antibacterial approaches. However, the photodynamic efficiency of conventional photosensitizer is often compromised by aggregation-induced quenching effects. Photosensitizers, especially natural products, with aggregation-induced emission (AIE) properties open a new avenue for photodynamic sterilization. Herein, we investigated the photodynamic antibacterial performance and mechanism of the AIE-type natural product of berberine (BBR) against Listeria monocytogenes (L. monocytogenes). The bactericidal effect was assessed through the determination of minimum bactericidal concentration and implementation of anti-biofilm experiments. The results showed that BBR can significantly suppress the proliferation of L. monocytogenes and can efficiently remove the L. monocytogenes-derived biofilm in a concentration-dependent trend. The mechanism of killing L. monocytogenes has been speculated based on bacterial morphology characterization, viability staining results, enzyme activity assays, DNA electrophoresis analysis, and molecular docking. The excellent anti-bacterial activity of BBR mediated photodynamic process may account for its abilities to the irreversibly disruption of bacterial membrane, inhibition of intracellular enzyme activity and decomposition of intracellular DNA molecules. We also demonstrated that BBR embedded sodium alginate/chitosan packaging film is feasible to maintain the freshness of salmon under light illumination by inhibiting the bacterial proliferation.

Influence of Steric Effects on the Emission Behavior of Pyrene-Based Blue Luminogens.

Pyrene-based derivatives have been widely deployed in organic luminescent materials because of their bright fluorescence, high charge carrier mobility, and facile modification. Nevertheless, the fluorescence output of conventional pyrenes is prone to quenching upon aggregation due to extensive intermolecular π-π stacking interactions. To address this issue, a set of new Y-shaped pyrene-containing luminogens are synthesized from a new bromopyrene chemical precursor, 2-hydroxyl-7-tert-butyl-1,3-bromopyrene, where the bromo and hydroxyl groups at the pyrene core can be readily modified to obtain the target products and provide great flexibility in tuning the photophysical performances. When the hydroxy group at the 2-position of pyrene was replaced by a benzyl group, the steric hindrance of the benzyl group not only efficiently inhibits the detrimental intermolecular π-π stacking interactions but also rigidifies the molecular conformation, resulting in a narrow-band blue emission. Moreover, the TPE-containing compounds 2c and 3c possessed characteristic aggregation-induced emission (AIE) properties with fluorescence quantum yields of up to 66% and 38% in the solid state, respectively. Thus, this article has methodically investigated the factors influencing the optical behavior, such as intermolecular interactions, and the steric effects of the substituent group, thereby opening up the potential to develop narrow-band pyrene-based blue emitters for OLED device applications.

Malachite green: a long-buried water-soluble AIEgen with near-infrared fluorescence for living cell nucleus staining.

Fluorescent imaging probes are crucial for exploring nucleus-related cellular events in live cells. Ideal probes should be photostable, small-sized, highly contrasted, and low in background. Here, we discovered that malachite green is a water-soluble near-infrared luminogen with aggregation-induced emission properties. Importantly, it can be used for living cell nucleus staining in a wash-free manner.

Precise molecular engineering for the preparation of pyridinium photosensitizers with efficient ROS generation and photothermal conversion.

Organic photosensitizers (PSs) with aggregation-induced emission properties have great development potential in the integrated application of multi-mode diagnosis and treatment of photodynamic therapy (PDT) and photothermal therapy (PTT). However, preparing high-quality PSs with both optical and biological properties, high reactive oxygen species (ROS) and photothermal conversion ability are undoubtedly a great challenge. In this work, a series of pyridinium AIE PSs modified with benzophenone have been synthesized. A wide wavelength range of fluorescent materials was obtained by changing the conjugation and donor-acceptor strength. TPAPs5 has a significant advantage over similar compounds, and we have also identified the causes of high ROS generation and high photothermal conversion in terms of natural transition orbitals, excited state energy levels, ground-excited state configuration differences and recombination energy. Interestingly, migration of target sites was also found in biological imaging experiments, which also provided ideas for the design of double-targeted fluorescent probes. Therefore, the present work proposed an effective molecular design strategy for synergistic PDT and PTT therapy.

Redox regulation of electrofluorochromic behavior for an AIEgen-doped PVA hydrogel based on a ferrocene derivate

The fluorescent molecule FcMe-TPE with aggregation-induced emission properties was synthesized to prepare an EFC hydrogel material with high conductivity. The obtained hydrogel exhibited reversible fluorescent switching behavior on external stimulus.