Emission Enhancement Properties Research Articles

A Multimode fluorescent sensor for sequential detection of Cu2+ and cysteine as well as pH sensor with real sample Applications: Extensive experimental and DFT studies

Highly responsive and optically selective (E)-1-((4-phenoxyphenyl) diazenyl)naphthalen-2-ol) sensor PDN with aggregation induced emission enhancement (AIEE) properties has been developed for the sequential detection of Cu2+ and L- Cysteine through fluorescence On-Off-On strategy. The selectivity of sensor depends on the presence of a diazo functional group and its appropriate cavity location in sensor molecule. Azo dye-based (E)-1-((4-phenoxyphenyl) diazenyl)naphthalen-2-ol) sensor PDN has been synthesized by utilizing a simple diazotization synthetic methodology that showed extraordinary AIEE behavior with bathochromic shift owing to the formation of J-aggregates. The morphology and size of aggregates were analyzed by SEM and DLS analysis, respectively. The calculated LOD of sensor PDN for Cu2+, and L-cysteine is 0.113 nM, and 84 nM, respectively. Fluorescence, UV–visible, 1H and 13C NMR titration were carried out to understand the interaction of sensor with Cu2+. The sensor was practically utilized in the sequential sensing of Cu2+ and Cys in real samples. Interestingly, sensor PDN was successfully employed for the sensing of a strong acid and base as well as the detection of Cu2+ ions in the solid state. Moreover, these experimental results were supported through DFT calculations.

An Acid-Responsive Fluorescent Molecule for Erasable Anti-Counterfeiting.

A tetraphenylethylene (TPE) derivative, TPEPhDAT, modified by diaminotriazine (DAT), was prepared by successive Suzuki-Miyaura coupling and ring-closing reactions. This compound exhibits aggregation-induced emission enhancement (AIEE) properties in the DMSO/MeOH system, with a fluorescence emission intensity in the aggregated state that is 5-fold higher than that of its counterpart in a dilute solution. Moreover, the DAT structure of the molecule is a good acceptor of protons; thus, the TPEPhDAT molecule exhibits acid-responsive fluorescence. TPEPhDAT was protonated by trifluoroacetic acid (TFA), leading to fluorescence quenching, which was reversibly restored by treatment with ammonia (on-off switch). Time-dependent density functional theory (TDDFT) computational studies have shown that protonation enhances the electron-withdrawing capacity of the triazine nucleus and reduces the bandgap. The protonated TPEPhDAT conformation became more distorted, and the fluorescence lifetime was attenuated, which may have produced a twisted intramolecular charge transfer (TICT) effect, leading to fluorescence redshift and quenching. MeOH can easily remove the protonated TPEPhDAT, and this acid-induced discoloration and erasable property can be applied in anti-counterfeiting.

Rational design of narrowband deep blue MR-TADF dendrimers for high performance solution-processed all fluorescence white OLEDs

Developing solution-processable deep-blue multiple resonances thermally activated delayed fluorescence (MR-TADF) is a formidable challenge. Here, we using a convergent synthesis process successfully developed a series of MR-TADF dendrimers based on C=O/N resonant core (QAO). The alkyl chain alternate-linked functional dendrons not only ensure the narrow-band deep-blue emission but also enable the dendrimers with aggregation-induced emission enhancement (AIEE) properties, which efficiently mitigate the aggregation-induced exciton quenching (ACQ) and obnoxious spectral redshift broadening effect. Notably, the solution-processed deep blue MR-TADF OLEDs achieved a maximum external quantum efficiency (EQE) of 13.5 % and CIE of (0.15, 0.12) with an electroluminescence peak below 450 nm. Further using such dendrimer as a sensitizer for white OLEDs resulted in an optimized high EQE of 18.9 % and a high color-rendering index (CIR) of 81.1 for two and three optical components of white emissions, which are among the highest values of previously reported solution-processed all-fluorescence white OLEDs. This is the first attempt to construct white OLED based on an MR-TADF emitter and the satisfactory results indicate that the flexible dendron engineering strategy can effectively develop high-performance narrow band deep-blue MR-TADF for wide-color gamut display and high CIR white OLEDs.

Base‐Promoted Regioselective Synthesis of α‐Amino BODIPYs through Cross‐Dehydrogenative Coupling with Anilines

AbstractThe construction of C−N bond at the α‐position of BODIPYs (boron dipyrromethene) not only enables flexible reactivity but also leads to strong electron‐donating properties. In this study, a base‐promoted oxidative cross‐dehydrogenative coupling was developed to synthesize α‐amino BODIPYs with air as a green oxidant. By this strategy, a series of weak nitrogen nucleophiles, such as heteroaryl and aryl anilines, were installed to the α‐position. Remarkably, pyrrole, pyrazole and indole were also employed to realize the synthesis of α‐heteroaryl BODIPYs through direct functionalization. Further aggregation‐induced emission enhancement (AIE) properties and lipid droplet‐targeting bioimaging experiments of representative dyes demonstrated their potential applications as organic probes.

A new luminescent nickel nanocluster with solvent and ion induced emission enhancement toward heavy metal analysis

Expanding the family of fluorescent metal clusters beyond gold, silver, and copper has always been an issue for researchers to solve. In this study, a novel type of cysteine-capped nickel nanoclusters (Cys-Ni NCs) with bright turquoise emission was developed. The as-synthesized Ni NCs showed aggregation-induced emission enhancement (AIEE) properties across Cd2+ and various polar organic solvents. Concurrently, solvents with different viscosities were used to explore the principle of solvent-induced AIEE of Cys-Ni NCs, revealing a positive correlation between fluorescence intensity and solution viscosity. In addition, the concentration of Cd2+ that induced the AIEE effect was reduced by nearly two orders of magnitude in highly viscous solvents, indicating the possibility of Cys-Ni NCs as a promising nanomaterial platform for Cd2+ sensing analysis. Moreover, we propose a novel fluorescent sensing method for rapid detection of Cu2+ based on the carboxyl group of Cys-Ni NCs coupling with Cu2+. Further, validation of Cu2+ detecting methodologies in environmental water samples with the accuracy up to 93.94% underscores their potential as robust and efficient sensing platforms. This study expands the repertoire of fluorescent metal nanoclusters for highly sensitive and selective sensing of hazardous ions and paves the way for further exploration and wide applications in Cu2+ detection in biological and medicine fields.

A triphenylamine derivative with multistimuli responsive behavior and high-contrast vapochromism of its Zn(II) complex

In this work, we designed and synthesized a novel multifunctional molecule, (E)-2-(4-(diphenylamino)styryl)-5-(4-pyridyl)-8-quinolinol (HL), which possessed D-π-A structure and exhibited optical responses to acid-base vapor and Zn(II) ions. Zn(II) complex of HL (W1) was obtained and characterized by SC-XRD. Spectral experiments demonstrated that complex W1 displayed aggregation-induced emission enhancement (AIEE) property, which was exact opposite to the aggregation-caused quenching effect of HL. The quantum yield of W1 (15%) was much higher than that of HL (2.1%) in the solid state. Both HL and complex W1 involved sp2 hybrid N atoms, whose protonation and deprotonation gave rise to reversible acidochromism with high contrast. The mechanism was clarified by XPS, 1H NMR, infrared spectroscopy, elemental analysis, PXRD and thermogravimetry results. Benefiting from excited state intramolecular proton transfer in HL together with AIEE of W1, HL could recognize Zn(II) sensitively in aqueous media. The detection limit of HL for Zn(II) reached as low as 5.02 × 10−8 M. An anti-counterfeiting application was realized using HL-loaded test strip, which exhibited fluorescence response, but no color change upon exposure to Zn(II) solution. In addition, HL and W1 solids were combined to develop a stimuli induced encryption/decryption strategy successfully based on their reversible acidochromic behaviors.

Investigating structural dynamics and sensing capabilities: Spectroscopic and DFT analysis of novel AIEE active deferasirox based organic sensor

A deferasirox based sensor DPA was rationally designed through single step amidation reaction. Sensor DPA exhibited aggregation induced emission enhancement (AIEE) property that was attributed to restriction in intramolecular rotation (RIR). Moreover, the sensor DPA displayed remarkable bathochromic shift (red-shift) of 110 nm in wavelength, ascribed to formation of J-aggregates. Furthermore, sensor DPA was employed for the selective and sensitive fluorescence based sensing of hazardous and carcinogenic nitrobenzene (NB). The sensor DPA successfully detected NB in solution through the quenching of emission intensity. The quenching of sensor fluorescence intensity was ascribed to photoinduced electron transfer (PET) mechanism. The sensing mechanism was investigated by 1H NMR titration experiment, Job's plot and density functional theory (DFT) calculations. Additionally, the existence of non-covalent interactions between sensor DPA and NB were examined by Bader's Quantum theory of atoms in molecules (QTAIM) and non-covalent interaction (NCI) analysis. Finally, sensor DPA was employed for the detection of volatile nitrobenzene in vapor phase.

An Ultra-low Detection Limit Fe3+ Optical Fiber Fluorescent Sensor Based on a Anti-B18H22 Derivative withAggregation-inducedEmission Enhancement.

A fluorescent Fe3+ probe ((C10H7NO2)2B18H20, M1) by introducing two isoquinoline-1-carboxylic acid group into the 6,9-position of anti-B18H22 was designed and synthesized. The structure of M1 was investigated by 1H NMR, MS, FT-IR and theoretical calculation, and its optical properties were characterized with UV-Vis and PL. M1 showed aggregation induced emission enhancement (AIEE) properties in THF/H2O solution, and exhibited an excellent selectivity toward Fe3+ in THF/H2O (v/v, ƒw = 95%) solution with a detection limit of 1.93 × 10-5M. The interaction mechanism of probe for detecting Fe3+ is attributed to the involvement of intramolecular charge transfer (ICT) process. Furthermore, a optical fiber fluorescent Fe3+ sensor based on M1 sensing film was developed, the detection limit of the optical fiber Fe3+ fluorescent sensor could be improved to13.8pM, the ultra-low detection limit is superior to most reported fluorescent probes (or sensors) towards Fe3+. This method has the advantages of high sensitivity, anti-interference and easy to operate, and has great potential in the field of the analysis of environmental and biological samples.

Regulable high-contrast mechanofluorochromic enhancement behaviour based on substituent effects.

Herein, a facile strategy was established to build mechanoresponsive luminogens with high sensitivity to substituents and positional effects. Even in slightly different structures, distinct optical phenomena, including fluorescence efficiency and mechano-responsive properties, were clearly present. Outstanding mechanical-induced emission enhancement (5-100 times) properties and reversibility makes for promising applications in pressure sensors and OLEDs.

Zn-Salphen Acrylic Films Powered by Aggregation-Induced Enhanced Emission for Sensing Applications

Zn(II) complexes possess attractive characteristics for supramolecular chemistry, catalysis, and optoelectronic applications, while Zn-Salphen counterparts are also suitable as chemical sensors, although limited by solution-based to date. In this study, we report the synthesis of new polymers from methyl methacrylate, n-butyl acrylate, and a non-symmetrical Zn-Salphen complex. We show that this low-fluorescent complex exhibits aggregation-induced emission enhancement (AIEE) properties and that, the incorporation of AIEE complexes into a polymeric matrix make it possible to achieve fluorescent films with enhanced fluorescence suitable for sensing applications. As a proof of concept, these films could detect acetic acid, showing a decrease of up to 73% in the original fluorescence. Host/guest studies showed a subtle disruption of the emission in aggregates upon treatment with anion guests. These results indicate that an interaction between the guest and Zn-Salphen complex may occur, stabilizing or destabilizing the complex and causing a concomitant increase or decrease in emission.

2,3-Diphenylquinoxalin-6-yl based dyes: Synthesis and studies of photophysical, aggregation-induced emission enhancement and electrochemical properties

Herein, 2,3-diphenylquinoxalin-6-yl based derivatives were synthesized, characterized by various spectroscopic method and studied for photophysical, aggregation-induced emission enhancement (AIEE) and electrochemical properties. Existence of intramolecular charge transfer transition (ICT) at 372−379 nm in absorption spectra of molecules confer weak push-pull interaction within it. Broad range of emission from blue to orange with λem = 412−592 nm in dyes arose from different energy state emission viz., locally excited (LE), Twisted intramolecular charge transfer (TICT) and excimer emission. Switching in emission state of molecules from excimer to TICT emission were observed by changing the polarity of solvent due to stabilization of TICT in polar media. Dyes have good solid state emission and AIEE activity desirable for its solid/aggregate state application in OLED's. Good Stokes shift (2183−9703 cm−1), thermal stability and comparable HOMO (−5.65 to −6.02 eV) energy levels with reported hole transporting materials confer desirable role of molecules in various optoelectronic applications. Further, DFT calculation of dyes, designate comparable experimental and theoretical photophysical and electrochemical properties with respect to structure of dyes.

A ratiometric luminescence probe for selective detection of Ag+ based on thiolactic acid-capped gold nanoclusters with near-infrared emission and employing bovine serum albumin as a signal amplifier.

When thiolactic acid-capped gold nanoclusters (AuNCs@TLA) with strong near-infrared (NIR, 800nm) emission were applied to detect metal ions, only Ag+ induced the generation of two new emission peaks at 610 and 670nm in sequence and quenching the original NIR emission. The new peak at 670nm generated after the 800-nm emission disappeared utterly. The ratiometric and turn-on responses showed different linear concentration ranges (0.10-4.0μmol·L-1 and 10-50μmol·L-1) toward Ag+, and the limit of detection (LOD) was 40nmol·L-1. Especially, the probe exhibited extremely high selectivity and strong anti-interference from other metal ions. Mechanism studies showed that the novel responses were attributed to the anti-galvanic reaction of AuNCs to Ag+ and formation ofbimetallic nanoclusters. Thetwo new emission peaks were due to the composition change and size growth of the metal core. Besides, bovine serum albumin (BSA) has been employed as a signal amplifier based on the assembly-induced emission enhancement properties of AuNCs, which improved the LOD to 10nmol·L-1. Moreover, the ratiometric method is feasible for Ag+ detection in diluted serum with high recovery rates, showing large application potential in the biological system. The present study supplies a novel ratiometric probe forAg+ with a two-stage response and provides a novel signal amplifier of BSA, which will facilitate and promote the application of NIR-emitted metal nanoclusters in biological system.

Unraveling the substituent group effects on the emission properties of fluorenone derivatives

Elucidating the structure–property relationship is vital for developing organic luminescent materials with excellent properties and performance optimization. Herein, we designed and synthesized three types of fluorenone-based molecules named FO-Ph, FO-Na and FO-An, with similar structures but different sizes of substituent groups (benzene, naphthalene and anthracene). This slight modification resulted in significantly different optical properties of luminogens in dilute solutions and powders. FO-Ph as an aggregation-caused quenching (ACQ) emitter displayed strong emissions in solution; moreover, after the addition of a poor solution, the fluorescence intensity of FO-Ph gradually decreased. On the contrary, FO-Na displayed aggregation-induced emission enhancement properties, and FO-An was non-emissive in solutions but displayed enhanced emission owing to its molecular aggregation, indicating that FO-An comprises an AIE-active molecule. The characterization of the photophysical properties, theoretical calculations and an X-ray single crystal analysis showed that the emission properties of the three compounds could be affected by the size of substituent groups, twisted geometry and molecular packing modes. The three fluorenone luminogens exhibited different force-induced emission enhancement properties. Moreover, FO-Ph can be used as a water detector and showing high sensitivity. This study elucidates the AIE and ACQ phenomena of fluorenone complexes and provides effective ways for developing organic luminescent materials.

Synthesis, tuning of photophysical and electrochemical properties of Yellow-Red emissive, AIEE active benzamide dyes

Herein, Benzamide-based dyes were prepared by the multistep synthetic method and then characterized by various spectroscopic methods. The tuning in photophysical, aggregation-induced emission enhancement (AIEE) and electrochemical properties with alteration in molecular structure of dyes were studied in detail. Molecules possess weak push–pull interaction due to the existence of inbuilt charge transfer (CT) transition at 366–387 nm in absorption spectra. Dyes emit in yellow to red region with emission maxima at 560–599 nm in solution and 548–600 nm in the solid state. The notable positive solvatochromic effect and good Stoke’s shift (9004–9717 cm−1) observed in dyes. Additionally, the existence of good solid-state emission and AIEE activity is desirable for its solid/aggregate state application in Organic light-emitting diodes. Besides, HOMO (−5.60 to − 5.74 eV) and LUMO (−3.14 to − 3.17 eV) energy levels comparable with reported ambipolar materials. Density functional theory (DFT) and time-dependent density-functional theory (TDDFT) calculations agree with the experimental photophysical and electrochemical data. The opto-electrochemical properties possessed by dyes undersign its suitable use in various optoelectronic applications.

Carbon dots-based fluorescence enhanced probe for the determination of glucose

In this work, a novel “turn-on” fluorescence sensor for the detection of H2O2 and glucose was developed based on green fluorescent carbon dots (CDs). The CDs was newly prepared by a facile one-pot hydrothermal method with Eosin Y and branched polyethylenimine as precursors. Interestingly, in the presence of H2O2 and HRP, the fluorescence of the CDs enhanced significantly with a red-shift emission due to their “aggregation”. Meanwhile, the oxidation of glucose catalyzed by glucose oxidase could generate H2O2. Thus, a simple sensing system based on the CDs as fluorescent probes was constructed for H2O2 and glucose determination, avoiding the fluorescence quenching and subsequent recovery process in conventional turn-on strategy. The method showed good selectivity and sensitivity for glucose sensing with the detection limit of 0.12 μM. The method was further applied to glucose detection in real samples. The obtained results demonstrated the simplicity, selectivity and practicality of the method. This work expands the carbon nanomaterials with fluorescence emission enhancement properties. It provides a new and direct “turn-on” strategy for H2O2 and glucose detection, which could be a simple and effective tool for screening biological substances involved in H2O2-generation reaction.

Dibenzthiophene and carbazole modified dicyanoethylene derivative exhibiting aggregation-induced emission enhancement and mechanochromic luminescence

A novel D-A type dicyanoethylene derivative DBT-Cz-DCN was designed and synthesized using dibenzthiophene, dicyanoethylene and carbazole as raw materials. Photophysical studies indicated that the luminogen DBT-Cz-DCN possessed unique intramolecular charge transfer (ICT) characteristic from electron donating carbazole unit to electron accepting dicyanoethylene moiety and aggregation-induced emission enhancement (AIEE) property. Theoretical calculations indicated that DBT-Cz-DCN exhibited a highly twisted conformation due to the steric hindrance effect of the dicyanoethylene unit. It was worth noting that DBT-Cz-DCN also exhibited distinct mechanochromic luminescence property. Specifically, when the pristine powder of DBT-Cz-DCN underwent grinding, the emitting color shifted from yellow to orange-yellow. The emitting color and wavelength could be restored to the pristine state after fuming with dichloromethane vapor. Powder X-ray diffraction confirmed that the transformation between the amorphous state and the crystalline state under external force stimuli was the reason for the MCL (mechanochromic luminescent) behavior of DBT-Cz-DCN. The current work not only developed a novel molecular structure with AIEE characteristic and MCL behavior, but also laid the foundation for the development of MCL materials with high contrast, high luminescence efficiency and good reversibility.

AIEE-Active Flavones as a Promising Tool for the Real-Time Tracking of Uptake and Distribution in Live Zebrafish.

In recent years, aggregation-induced emission enhancement (AIEE) molecules have shown great potential for applications in the fields of bio-detection, imaging, optoelectronic devices, and chemical sensing. Based on our previous studies, we investigated the fluorescence properties of six flavonoids and confirmed that compounds 1-3 have good aggregation-induced emission enhancement (AIEE) properties through a series of spectroscopic experiments. Compounds with AIEE properties have addressed the limitation imposed by the aggregation-caused quenching (ACQ) of classic organic dyes owing to their strong fluorescence emission and high quantum yield. Based on their excellent fluorescence properties, we evaluated their performance in the cell and we found that they could label mitochondria specifically by comparing their Pearson correlation coefficients (R) with Mito Tracker Red and Lyso-Tracker Red. This suggests their future application in mitochondrial imaging. Furthermore, studies of uptake and distribution characterization in 48 hpf zebrafish larvae revealed their potential for monitoring real-time drug behavior. The uptake of compounds by larvae varies significantly across different time cycles (between uptake and utilization in the tissue). This observation has important implications for the development of visualization techniques for pharmacokinetic processes and can enable real-time feedback. More interestingly, according to the data presented, tested compounds aggregated in the liver and intestine of 168 hpf larvae. This finding suggests that they could potentially be used for monitoring and diagnosing liver and intestinal diseases.

Nobiletin with AIEE Characteristics for Targeting Mitochondria and Real-Time Dynamic Tracking in Zebrafish.

Nobiletin is a natural product with multiple physiological activities and is the main ingredient of Pericarpium Citri Reticulatae. We successfully discovered that nobiletin exhibits aggregation induced emission enhancement (AIEE) properties and it has significant advantages such as a large Stokes shift, good stability and excellent biocompatibility. The increase in methoxy groups endows nobiletin a greater fat-solubility, bioavailability and transport rate than the corresponding unmethoxylated flavones. Ulteriorly, cells and zebrafish were used to explore the application of nobiletin in biological imaging. It emits fluorescence in cells and is specifically targeted at mitochondria. Moreover, it has a noteworthy affinity for the digestive system and liver of zebrafish. Due to the unique AIEE phenomenon and stable optical properties of nobiletin, it paves the way for discovering, modifying and synthesizing more molecules with AIEE characteristics. Furthermore, it has a great prospect with regard to imaging cells and cellular substructures, such as mitochondria, which play crucial roles in cell metabolism and death. Indeed, three-dimensional real-time imaging in zebrafish provides a dynamic and visual tool for studying the absorption, distribution, metabolism and excretion of drugs. In this article, more directions and inspiration can be presented for the exploration of non-invasive pharmacokinetic research and intuitive drug pathways or mechanisms.

Y-Shaped D-A Type Thioxanthone Derivatives: Mechano-Induced Thermally Activated Delayed Fluorescence and High-Contrast Mechano-Responsive Luminescence.

High-contrast mechano-responsive luminescence (MRL) materials with mechano-induced emission enhancement properties are fascinating candidates but few, for applications in rewritable media and recording devices. Here, an interesting design strategy of "Y-shape" donor-acceptor (D-A) type molecules for high-contrast MRL materials was presented, based on substituted diphenylamine donor and planar acceptor. Interestingly, their D-A torsion angles are small in crystals but increased after ground, resulted in planar and twist intramolecular charge transfer (PICT and TICT) states, respectively. Therefore, high-contrast MRL switching between weak blue (450 nm) fluorescence and bright yellow (552 nm) thermally activated delayed fluorescence (TADF) can be achieved for compound TXDO (4,4'-dimethoxydiphenylamine donor), which photoluminescence quantum yield increased from 2.8% to 54.7% after ground. Most importantly, the two independent D-A conjugation dihedral angles are actually independent in the "Y-shape" molecules. Especially for compound TXDT (4,4'-di-tert-butyldiphenylamine donor), its crystal exhibited both PICT and TICT processes inside, resulted from the different dihedral angles of 11.8° and 35.5°, respectively. The TXDT crystal thus showed dual-peak emission, including both TICT fluorescence and PICT room-temperature phosphorescence. Therefore, this strategy of "Y-shape" D-A type molecules provide a new approach to design advanced luminescent materials with mechano-induced TADF feature, for high-contrast MRL and single-component white luminescence.

Structure-Property Relationship of Macrocycles in Organic Photoelectric Devices: A Comprehensive Review.

Macrocycles have attracted significant attention from academia due to their various applications in organic field-effect transistors, organic light-emitting diodes, organic photovoltaics, and dye-sensitized solar cells. Despite the existence of reports on the application of macrocycles in organic optoelectronic devices, these reports are mainly limited to analyzing the structure-property relationship of a particular type of macrocyclic structure, and a systematic discussion on the structure-property is still lacking. Herein, we conducted a comprehensive analysis of a series of macrocycle structures to identify the key factors that affect the structure-property relationship between macrocycles and their optoelectronic device properties, including energy level structure, structural stability, film-forming property, skeleton rigidity, inherent pore structure, spatial hindrance, exclusion of perturbing end-effects, macrocycle size-dependent effects, and fullerene-like charge transport characteristics. These macrocycles exhibit thin-film and single-crystal hole mobility up to 10 and 26.8 cm2 V-1 s-1, respectively, as well as a unique macrocyclization-induced emission enhancement property. A clear understanding of the structure-property relationship between macrocycles and optoelectronic device performance, as well as the creation of novel macrocycle structures such as organic nanogridarenes, may pave the way for high-performance organic optoelectronic devices.