Aggregation-induced Emission Properties Research Articles

Cellulose nanofiber-templated metal-organic frameworks for fluorescent detection of methyl parathion pesticides

Methyl parathion is a typical organophosphorus pesticide that poses threats to the global environment and human health. In this study, we developed a portable 2D sensing pad for monitoring methyl parathion based on the aggregation-induced emission (AIE) properties of an innovated hybrid material that integrates cellulose nanofibers (CNFs) with luminescent metal-organic frameworks (LMOFs). The hybrid material enhanced the flexibility and moldability of LMOFs and significantly improved the scalability of sensing material. The resulting CNF/LMOF material was shaped into a 2D pad, exhibiting fluorescent properties under UV exposure. The fluorescence of the pad was quenchable upon exposure to methyl parathion. This host-guest interaction enabled the precise quantification of the pesticide’s concentration by monitoring the intensity variation of the fluorescence at 405 nm wavelength. We further engineered these hybrid pads into a user-friendly and portable sensing prototype, and then validated them with real sample testing. Time-dependent Density Functional Theory calculations were employed to elucidate the underlying fluorescence quenching mechanism triggered by methyl parathion. This work introduces a practical and sustainable sensing platform for pesticide detection.

Aggregation-induced-emission red carbon dots for ratiometric sensing of norfloxacin and anti-counterfeiting

The detection of trace antibiotic residues holds significant importance because it’s related to food safety and human health. In this study, we developed a new high-yield red-emitting carbon dots (R-CDs) with aggregation-induced emission properties for ratiometric sensing of norfloxacin. R-CDs were prepared in 30 min using an economical and efficient microwave-assisted method with tartaric acid and o-phenylenediamine as precursors, achieving a high yield of 34.4 %. R-CDs showed concentration-dependent fluorescence and aggregation-induced-emission properties. A ratiometric fluorescent probe for detecting the norfloxacin was developed. In the range of 0–40 μM, the intensity ratio of two emission peaks (I445 nm/I395 nm) towards norfloxacin show good linear relationship with its concentrations and a low detection limit was obtained (36.78 nM). In addition, complex patterns were developed for anti-counterfeiting based on different emission phenomenon at different concentrations. In summary, this study designed a novel ratiometric fluorescent probe for detection of norfloxacin, which greatly shortens the detection time and improves efficiency compared with high-performance liquid chromatography and other methods. The study will promote the application of carbon dots in anti-counterfeiting and other related fields, laying the foundation for the preparation of low-cost photosensitive anti-counterfeiting materials.

A thermochromic salicylaldehyde Schiff bases derivative with AIE properties due to twisted structure

Great attention has been attracted to the salicylaldehyde Schiff base due to its thermochromic and photochromic characteristics in the solid state. However, the boundary between photochromic and thermochromic salicylaldehyde Schiff base structures is still unclear, and few studies have been conducted to investigate their thermochromic behavior and structures in depth and systematically. In the present work, we have synthesized a novel salicylaldehyde Schiff base derivative (2,2′-((1E,1′E)-((2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diyl)-bis(azaneylylidene))bis(methaneylylidene))diphenol, BTB) with twisted structure, which possesses both thermochromic and aggregation-induced emission (AIE) characteristics, and systematically investigated its thermochromic properties, enol-keto isomerization, AIE properties, aggregated state, and excited state intramolecular proton transfer (ESIPT) process. Interestingly, in our study, we found that the color of the BTB molecule changed gradually during the heating process, and it can be found that the thermochromism of BTB is produced by the reversible equilibrium shift of the enol form and the keto forms due to the temperature change by the color difference test, the in-situ IR spectra and the DSC curves. Finally, the pathway of BTB proton transfer was analyzed through quantum chemical calculations, and it was found that enol ketone isomerization is achieved through single excited state intramolecular proton transfer, rather than the expected double excited state intramolecular proton transfer.

D-π-A type dicyanoethylene derivatives modified by tetraphenylethylene exhibiting aggregation-induced emission and high-contrast mechanofluorochromism

Based on a rational design strategy by combining an electron-withdrawing dicyanoethylene unit and electron-donating tetraphenylethylene moiety, we successfully synthesized two π-conjugated molecules Ph-TPE-MMN and NA-TPE-MMN. According to the optical research and theoretical calculation results, they had highly distorted conformations, D-A type molecular structure and definite intramolecular charge transfer (ICT) properties. Moreover, two molecules Ph-TPE-MMN and NA-TPE-MMN showed aggregation-induced emission (AIE) properties in the THF/water mixture at higher fw (water fraction). Ph-TPE-MMN and NA-TPE-MMN also exhibited fluorescence response to external force. The emitting color of both had changed greatly before and after grinding. The maximum emission wavelengths of Ph-TPE-MMN and NA-TPE-MMN were redshifted by 46 nm and 33 nm, respectively, implying high-contrast mechanofluorochromism. Notably, mechanofluorochromic process also showed a good reversible. XRD experiments indicated that mechanofluorochromic mechanism originated from changes in molecular stacking in solid state.

A supramolecular photosensitizer based on triphenylamine and pyrazine with aggregation-induced emission properties for high-efficiency photooxidation reactions

Recently, there has been a great interest in the study of photocatalysts (PCs) and photosensitizers (PSs) in the field of organic photocatalysis. In the present study, a pure organic thermally activated delayed fluorescence (TADF) molecule 4,4′-(12-(pyridin-4-yl)dibenzo[f,h]pyrido[2,3-b]quinoxaline-3,6-diyl)bis(N,N-diphenylaniline) (DPQ-TPA) was designed and synthesized, which not only have excellent TADF property and small energy splitting (ΔEST), but also can self-assembly in water to form cross-linked nanoparticles with exceptional aggregation-induced emission (AIE) characteristics. DPQ-TPA exhibits excellent remarkable selectivity and notably enhances the production capacity of reactive oxygen species (ROS), particularly 1O2, which was employed as a highly effective photocatalyst in the photooxidation reaction of phosphine and hydroazobenzenes under blue light irradiation with high yields up to 94% and 91%, respectively. This work expands the potential application of (donor-acceptor) D-A type AIE-TADF molecules in photocatalytic organic transformations through supramolecular self-assembly.

Mechanofluorochromic behaviors and data security protection properties of salicylaldimine-based difluoroboron complexes with different aryl substituents.

To further explore the relationship between aryl substituents and mechanofluorochromic (MFC) behaviors, four salicylaldimine-based difluoroboron complexes (ts-Ph BF2, ts-Ph-NA BF2, ts-2NA BF2, and ts-triphenylamine [TPA] BF2), including aromatic substituents with different steric hindrance effects, were designed and successfully synthesized. Four complexes with twisted molecular conformation displayed intramolecular charge transfer and aggregation-induced emission properties. Under external mechanical stimuli, the as-synthesized powders of ts-Ph BF2, ts-Ph-NA BF2, and ts-TPA BF2 exhibited redshift fluorescence emission behaviors, and ts-Ph BF2 and ts-TPA BF2 could be recovered to original shifts by fuming, but ts-Ph-NA BF2 displayed irreversible switching. ts-2NA BF2 had no change during the grinding and fuming processes. The results indicated that the MFC behaviors could be attributed to the phase transformation between the well-defined crystalline and disordered amorphous states by X-ray diffraction measurement. Further research illustrated that ts-TPA BF2 with the most significant MFC phenomenon could be applied in data security protection in ink-free rewritable paper.

Unlocking Diverse π-Bond Enrichment Frameworks by the Synthesis and Conversion of Boronated Phenyldiethynylethylenes.

The π-bond enrichment frameworks not only serve as a crucial building block in organic synthesis but also assume a pivotal role in the fields of materials science, biomedicine, photochemistry, and other related disciplines owing to their distinctive structural characteristics. The incorporation of various substituents into the C═C double bonds of tetrasubstituted alkenes is currently a highly significant research area. However, the synthesis of tetrasubstituted alkenes with diverse substituents on double bonds poses a significant challenge in achieving stereoselectivity. Here, we reported an efficient and convergent route of Cu-catalyzed borylalkynylation of both symmetrical and unsymmetrical 1,3-diynes, B2pin2, and acetylene bromide to the construction of boronated phenyldiethynylethylene (BPDEE) derivatives with excellent chemo-, stereo-, and regioselectivities. BPDEE derivatives could transform into novel tetrasubstituted organic π-conjugated gem-diphenyldiethynylethylene (DPDEE), vinylphenyldiethynylethylene (VPDEE), and phenyltriethynylethylene (PTEE) derivatives by a stepwise process, which provides a flexible platform for the synthesis of complex π-bond enrichment frameworks that were difficult to synthesize by previous methods. The initial optical characterization revealed that the synthesized molecules exhibited aggregation-induced emission (AIE) properties, which further establishes the groundwork for future applications and enriches and advances the field of functional π-conjugated frameworks research.

Bioprospecting of Chlamydomonas reinhardtii for boosting biofuel-related products production based on novel aggregation-induced emission active extracellular polymeric substances nanoprobes

Biofuel production from microalgae has been greatly restricted by low biomass productivity and long-term photosynthetic efficacy. Here, a novel strategy for selecting high-growing, stress-resistant algal strains with high photosynthetic capacity was proposed based on biocompatible extracellular polymeric substances (EPS) probes with aggregation-induced emission (AIE) properties. Specifically, AIE active EPS probes were synthesized for in-situ long-term monitoring of the EPS productivity at different algal growth stages. By coupling the AIE-based fluorescent techniques, algal cells were classified into four diverse populations based on their chlorophyll and EPS signals. Mechanistic studies on the sorted algal cells revealed their remarkable stress resistance and high expression of cell division, biopolymer production and photosynthesis-related genes. The sorted and subcultured algal cells consistently exhibited relatively higher growth rates and photosynthetic capacities, resulting in an increased (1.2 to 1.8-fold) algal biomass production, chlorophyll, and lipids. This study can potentially open new strategies to boost microalgal-based biofuel production.

Aggregation-Induced Emission of Naphthalene Diimides: Effect of Chain Length on Liquid and Solid-Phase Emissive Properties.

The aggregation-induced emission (AIE) properties of a systematic series of naphthalene diimides (NDIs) varying the chain length at the imide positions have been studied. A solvophobic collapse of NDI units through the flash injection of THF NDI solutions in sonicating water triggers the formation of stable suspensions with enhanced fluorescence emissions. Shorter chains favor the π-π stacking of NDI units through H-aggregation producing a strong AIE effect showing remarkably high quantum yields that have not been observed for non core-substitued NDIs previously. On the other hand, NDIs functionalized with longer chains lead to more disordered domains where π-π stacking between NDI units is mainly given by J-aggregation unfavoring the AIE effect.

3-Aroylbenzocoumarin-Based Luminogens: Bright Solid-State Emission, AIE Properties and Cell Imaging Application.

A series of 3-aroylbenzocoumarin-based luminogens have been synthesized for investigating their aggregation-induced emission (AIE) and solid-state fluorescence. The single crystal X-ray diffraction analysis of one of them showed that the molecules are arranged in the form of π-dimers which may lead to excimer emission. The large Stokes shifts and the broad-band emission of these 3-aroylbenzocoumarins in solid/aggregation state demonstrated the probable formation of excimers. The shapes of benzocoumarin units have a great effect on the AIE behaviors. The linear benzocoumarin derivatives show larger Stokes shifts, while the bent-benzocoumarin derivatives exhibit better AIE performances. All of them show aggregation-enhanced excimer emission which is supported by the large Stokes shifts. The electronic effect of 3-aroyl groups also has a certain effect on their fluorescence properties. The polymorphism phenomenon was observed for one of the benzoyl-containing derivatives. Additionally, two of the derivatives containing methoxy group were successfully used for cell imaging.

An AIE Controlled "Off-On" Cu2+-Sensitive Probe for Early Detection of Renal Fibrosis.

Early detection of renal fibrosis (RF) is very important given that it is irreversible when it progresses to the terminal stage. A key marker of RF pathogenesis is activation of myomyofibroblasts, and its targeted imaging may be a promising approach for early detection of RF, but no study has directly imaged activation of renal myomyofibroblasts. Cu2+ plays a major role in the fibrotic activity of myofibroblasts. Herein, inspired by that Cu2+ can complex with bovine serum albumin (BSA), BSA-Ag2S quantum dots (QDs) with aggregation-induced emission (AIE) property are synthesized. Then BSA-Ag2S QDs are modified by chitosan (CS) with renal targeting and hyaluronic acid (HA) with myofibroblast targeting to obtain the AIE assay system (QDs@CS@HA). The system is simple to synthesize, and produces a rapid NIR fluorescence signal turn-on response and a low detection limit of 75× 10-9 m to Cu2+. In addition, cellular and animal experiments have shown that QDs@CS@HA has good biosafety and cell-targeted imaging capability for RF. Based on the successful application of QDs@CS@HA and the mechanism of RF progression in early RF detection, it is expected that QDs@CS@HA may detect RF before the appearance of clinical symptoms.

Palladium-Copper-Catalyzed Oxidative Intermolecular [2 + 2 + 2] Coupling-Annulation: Regioselective Synthesis of Multiaryl-Substituted Benzenes.

A palladium-catalyzed intermolecular [2 + 2 + 2] oxidative coupling-annulation of terminal alkenes and alkynes using copper(II) as the oxidant has been developed through direct C-C bond formation. These reactions provide effective access to multiaryl-substituted benzenes with high regioselectivity in the absence of any ligands. The features of this protocol are broad substrate scope, and high atom and step economy. The aggregation-induced emission properties of selected products were further investigated. These synthesized multiaryl-substituted benzenes may be worth exploring for further applications in the fields of advanced functional materials or drugs.

TPE[2]arenes: Luminescent macrocyclic arenes with aggregation-induced emission and Al3+ detection

Luminescent macrocyclic arenes have attracted interest owing to their unique cyclic geometry and adaptive emission. Herein, a series of fluorescent macrocyclic arenes, denoted as TPE [2]arenes, were easily synthesized by the one-pot condensation of tetraphenylethene (TPE) moiety and paraformaldehyde in the presence of BF3·OEt2 and readily derivatized to yield cyclic arenes with diverse substitution patterns. The macrocyclic arenes shared similar cyclic skeleton with resorcin [4]arene, and existed as two enantiomers with boat conformation confirmed via single crystal analysis. Furthermore, TPE [2]arenes all retained the aggregation-induced emission properties owing to the incorporation of TPE moiety and obvious mechanochromic luminescence behavior due to the relative flexible skeleton. The carboxylic acid substituted analogues, namely TPE [2]arene-COOH, exhibited specific “turn-on” detection of Al3+ ion in aqueous media.

Donor-Acceptor Assembly of Amphiphilic Molecules Based on 9,10-Distyrylanthracene Derivatives with Terminal Naphthalene Groups.

Amphiphilic rod-coil compounds have excellent photophysical properties and can be assembled into supramolecular nanostructures of different sizes in water or polar solvents. Herein, we synthesized the amphiphilic compounds 2N-DSA, 4N-DSA, and 6N-DSA with 9,10-distyrylanthracene (DSA) as the core and a naphthalene unit as the terminal group that connected DSA through a tetraethylene glycol chain. These compounds have excellent aggregation-induced emission (AIE) properties in aqueous solution and are assembled into worm-like fragments or different sizes of spherical assemblies, defending the volume ratio of the rod to coil segments. Notably, the donor-acceptor interaction between DSA and electron- deficient compounds 2,4,6-trinitrophenol (TNP), 2,4,5,7-tetranitrofluorenone (TNF), and tetraethylene glycol dinitrobenzoate (TGDNB) forms a charge transfer complex, which can be used as a nanoreactor to improve the yield of the Suzuki coupling reaction about 8-10 times. The experimental results reveal that the synergy effect of the donor-acceptor, intermolecular π-π stacking, and hydrophobic-hydrophilic interactions significantly influences the morphology of aggregates and the efficiency of the nanoreactor.

Effects of a Larger N‐Heterocyclic Ring in Rofecoxib Analogues on AIE Activity and Multifunctional Applications

Two analogues of rofecoxib, 2‐Pyr‐ROF and 2‐Pip‐ROF, were designed according to the strategy of heterocyclic ring enlargement and facilely synthesized in a facile manner by Knoevenagel reactions. The first compound, 2‐Pyr‐ROF, had low quantum yields (QY) of 3.0% in the solid states. After replacing the pyrrolidinyl with piperidinyl, the resulting 2‐Pip‐ROF had a significantly increased QY, with a value of 28%. The root‐mean‐square deviation (RMSD) values between S0 and S1 of 2‐Pyr‐ROF and 2‐Pip‐ROF in tetrahydrofuran were 0.51, 0.35 Å, respectively. As compared with 2‐Pyr‐ROF, compound 2‐Pip‐ROF exhibits a smaller RMSD, which indicates a lower non‐radiative transition rate. A single‐crystal X‐ray diffraction study and Hirshfeld surfaces analysis revealed that 2‐Pip‐ROF had a more nonplanar molecule structure and a weaker π‐π interaction, which might result in a higher fluorescence intensity and QY. Owing to its better aggregation‐induced emission (AIE) behavior, compound 2‐Pip‐ROF showed more multi‐functional applications, including mechanochromism, acidochromism, and lipid droplets imaging ability. These results imply that the strategy of heterocyclic ring enlargement provides a new paradigm for the design of new luminogens with AIE properties.

C3 -Symmetric Luminescent Diketone with Amido-Linkage as a Polymorphic Fluorescence Emitter.

The study introduces a novel C3 -symmetric β-diketone compound, BTA-D3, and its monomeric counterpart, D, with a focus on their synthetic procedure, photophysical properties and aggregation behavior. Both compounds exhibit characteristic absorption and weak fluorescence in solution, with BTA-D3 displaying higher absorption coefficients due to its larger number of diketone units. Density Functional Theory (DFT) calculations suggest increased co-planarity of diketone groups in BTA-D3. A significant finding is the Aggregation-Induced Emission (AIE) property of BTA-D3, as its fluorescence intensity increases dramatically when exposed to specific solvent ratios. The AIE behavior is attributed to intermolecular excitonic interaction between BTA-D3 molecules in self-organized aggregates. We also studied fluorescence anisotropy of BTA-D3 and D. Despite its larger size, BTA-D3 showed reduced anisotropy values because of efficient intramolecular energy migration among three diketone units. Furthermore, BTA-D3 demonstrates unique polymorphism, yielding different emission colors and structures depending on the solvent used. A unique approach is presented for promoting the growth of self-organized aggregate structures via solvent evaporation, leading to distinct fluorescence properties. This research contributes to the understanding of C3 -symmetric structural molecules and provides insights into strategies for controlling molecular alignment to achieve diverse fluorescence coloration in molecular materials.

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.