Aggregation-induced Quenching Research Articles

Development of Polythiophene–Tripeptide Covalent Conjugates Showing Excellent Structure-Dependent Photophysical and Photocurrent Properties

Presently, conducting polymer–peptide conjugates have drawn great interest for their interesting optoelectronic and photophysical properties. To understand the structural dependence of the conjugates on their properties, we have covalently coupled poly(3-thiophene acetic acid) (P3TAA) with a C-protected tripeptide, H2N-F-F-V-OMe (TPEP), to produce their conjugate PTCP-I. A carboxylic acid-deprotected tripeptide polythiophene conjugate (PTCP-II) is also produced by alkaline hydrolysis of PTCP-I to delineate any difference in properties due to the change in molecular structure. The stretching frequencies for −NH– and >C═O groups of PTCP-II are 11 and 26 cm–1 lower than those of PTCP-I, indicating better intermolecular hydrogen bonding interactions in the former. This alters the seaweed morphology of PTCP-I to a sheet morphology for PTCP-II. The blue shift of the π–π* absorption band of polythiophene with gradually increasing the PTCP-I concentration is attributed to the H-type aggregation in DMF solution, but in the solid state, this peak shows a 17 nm red shift from its solution state for better electron delocalization for closer proximity of molecules. The UV–Vis peak of PTCP-II shows a lower blue shift than that of PTCP-I in DMF, attributed to the uncoiled polythiophene chains of the former. In DMF solution, interestingly, both PTCP-I and PTCP-II conjugates exhibit aggregation-induced emission (AIE), showing maxima at 0.08 mg/mL and then aggregation-induced quenching (AIQ) with further increasing its concentration. PTCP-I and PTCP-II exhibit dc conductivities of 0.04 and 0.55 μS cm–1, respectively, at 30 °C, and the higher value for PTCP-II is due to its lower band gap (1.91 eV) compared to that of PTCP-I (2.14 eV). The current (I)–voltage (V) plot of both conjugates exhibits semiconducting properties, which are higher for PTCP-II for its lower band gap. The photocurrent behavior of the conjugates indicates that the on–off response in the PTCP-II system is significantly higher than that in PTCP-I due to the unfolded polymer chain of the former, as the photogenerated electrons and holes can move more freely there. Impedance spectra of both the conjugates show single semicircles for the Nyquist plots, and the charge transfer resistance of PTCP-II is 4.4 times lower than that of PTCP-I but the capacitance value is 27 times higher, arising from the more extended chain configuration of the former, signifying structural importance on the optoelectronic and photocurrent properties of the polymer–peptide conjugates.

Beauty in chemistry: A self-organized and dual-phase emissive diketopyrrolopyrrole derivative as high-yield fluorescent material

In the long-span human history, “beauty” has always been the ultimate pursuit of mankind's civilization. In this work, we report the synthesis of a beautiful fluorescent material based on an old-brand pigment named diketopyrrolopyrrole (DPP) with a high yield up to 90%. The completely overlapping molecules, which in general case would cause aggregation-induced quenching (ACQ) effect, can unexpectedly emit in both solvent and solid state (solid-state fluorescent quantum yield up to 30%). The term “beauty” has been verified by various types of optical spectra, while luminescence mechanism is systematically investigated by single-crystal X-ray diffraction (XRD), time-dependent density functional theory (TD-DFT) calculation and concentration-dependent absorption/emission. A self-organization process is observed. The promising future for large scale production can be foreseeably met by its quick synthesis and satisfied yield.

Fulgide Derivative-Based Solid-State Reversible Fluorescent Switches for Advanced Optical Memory

Fulgide Derivative-Based Solid-State Reversible Fluorescent Switches for Advanced Optical Memory

Inversion in usual excitation intensities from solid state phosphor and improved fluorescence of Eu3+ ion in type (IV) deep eutectic solvent

To resolve the issue of aggregation induced quenching (AIQ), poor adhesion/dispersion on film and fiber, limited dispersability/solubility and non biocompatibility issue; phosphor powder particles are generally casted into solution form. It was found in most cases that lanthanide luminescence and lifetime reduced substantially in aqueous medium and ionic liquid. Deep eutectic solvent (DES) has been found to be an alternate and more efficient solvent for lanthanide luminescence. With similar intention we have synthesized europium type (IV) DES (EuDES) via mechanochemical synthesis employing europium nitrate and urea. Fourier transformed infrared spectroscopy (FTIR) studies confirms that in DES, the Eu3+ ion is surrounded by bidentate nitrate ions and urea is coordinated to europium centre by CO group. There is no water molecule in primary coordination sphere of Eu3+ ion. Interestingly with rigid H-bonding and strong chemical interaction offered by DES; Eu3+ CTB is quenched whereas very high intensity of Eu3+ intra f-f transition appears which was reversal from usual trend. Moreover asymmetry ratio was found to be more than 3 with predominantly high intensity of electric dipole transition (EDT) suggesting very asymmetric environment around Eu3+ in DES. But the distribution of europium was found to be very homogenous with luminescence lifetime of ~3.7 ms and point group symmetry ~ C6v. Judd-Ofelt analysis suggested very low non-radiative channels present in DES resulting in extremely high quantum yield ~76% and very high color purity of 94.72% which was also assisted by absence of any water molecule as suggested by FTIR measurement.

Protic acid-induced LCST rigid-chain polymeric gel with enhanced blue emission via weakened conjugation effect

Rigid-chain polymeric gels with excellent performance and multi-functions are rarely reported due to the difficulty in balancing solubility and precipitation caused by π-π stacking. Herein, a rigid aromatic polyamide organogel containing benzimidazole moiety was prepared successfully by utilizing protonation effect of protic acid HCl. Due to protonation, coplanarity of stacking structures was destroyed and the dissolution interaction of benzimidazole moiety and solvent was weakened. With increasing temperature, the further decreased solvation capacity led to the formation of interchain hydrogen bonds with a self-assembly process that induced gelation. What’ s more, due to weakened conjugation of protonated PABI, aggregation-induced quenching (ACQ) was suppressed, and this LCST-type organogel showed aggregation-induced emission (AIE) phenomenon with enhanced blue-light emission. This paper provides an ingenious approach via regulating conjugation and solvation for constructing functional rigid-chain polymer gels.

A Novel Fluorescence Tool for Monitoring Agricultural Industry Chain Based on AIEgens

With the development of the global economy, the safety of agricultural production has attracted intense attention. To minimize the risk of harmful ingredients in the whole industry chain, it is very necessary to cover the entire process of safety inspections from planting to production to environmental management. Fluorescence sensing as a promising and powerful screening tool is widely used for the detection of ions, toxic gases, biological molecules and so on. However, traditional fluorescent probes often suffer from aggregation-induced quenching(ACQ) effects, which limits their practical applications. In this regard, aggregation-induced emission luminogens(AIEgens) can perfectly address this notorious issue and have shown great potential in agricultural safety analysis. In this review, we briefly summarize their applications in agricultural safety monitoring, including the fabrication of agricultural film, agricultural sewage treatment and selective detection of harmful residues in agricultural products. The challenge and future development of AIEgens in this field are also discussed and highlighted. Hopefully, this review can inspire more researchers to participate in this fascinating area.

A New Strategy Using a Fluorescent Probe Combined with Polydopamine for Detecting the Activity of Acetylcholinesterase

A water-soluble and sensitive fluorescent probe N,N′-bis[tris-(2-aminoethyl)amine]-3,4,9,10-perylenetetracarboxylic diimide (PTRIS) was synthesized and, in combination with polydopamine (PDA), utilised in the detection of acetylcholinesterase (AChE) activity. PDA is spontaneously polymerized from dopamine (DA) in aerobic and alkaline solutions. The excellent absorption of PDA results in the aggregation of PTRIS around PDA as well as π–π stacking between them, which consequently quenched the fluorescence of PTRIS due to aggregation induced quenching (AIQ) in 9 min. The hydrolysis product of acetylthiocholine (ATCh) catalyzed by AChE, thiocholine (TCh), was proved to inhibit the polymerization of DA, therefore the free monomeric PTRIS retained its strong fluorescence intensity. The fluorescence was switched off and on depending on the activity of AChE. According to the change of fluorescence intensity at 550 nm, the detection limit of AChE was quantified as 0.02 mU mL−1. It was also proved that this probe possessed excellent selectivity for AChE. Tacrine and the organophosphate pesticide diazinon were further evaluated for inhibitor screening. The half-maximal inhibitory concentration value of tacrine and diazinon was calculated to be 1.4 and 1.6 μM respectively, revealing potential applications for inhibition and pesticide detecting.

AIE material for photodynamic therapy.

Photodynamic therapy (PDT) is emerging as an excellent strategy to treat different types of cancers. The advantages of using PDT over other cancer treatment modalities are owing to its non-invasive nature, spatiotemporal precession, controllable photoactivity, and least side effects. The photosensitization ability of traditional photosensitizers (PSs) are severely curtailed by aggregation-induced quenching (ACQ). On the contrary, aggregation induced emission (AIE) molecules/fluorogens (AIEgens) show enhanced fluorescence emission and high reactive oxygen species (ROS)/singlet oxygen (1O2) production capability in the aggregated state. These unique characteristics of AIEgens make them potential AIE-PSs for fluorescence/luminescence image-guided combination PDT. In this chapter, we discussed the strategies that are developed to synthesize small molecule-based AIE-PSs, metal complex-based AIE-PSs, and AIE-PSs with two-photon absorbance (TPA) properties, polymer-based AIE-PSs, and nanoparticles based AIE-PSs for PDT. We have also discussed the rational design of targeting peptide conjugated AIE-PSs to selective target cancer cells over normal cells. Furthermore, recent findings on nanoparticle-based combination AIE-PSs are also discussed, where the combination AIE-PSs show synergistically improved anticancer activity and overcome the drug resistance. Finally, we shed light on the recent development, ongoing challenges, and future directions for designing better AIE-PS for PDT.

A long-wavelength activable AIEgen fluorescent probe for HClO and cell apoptosis imaging.

Hypochlorous acid (HClO) is an important bactericide, and adjusting the content of HClO helps to improve the host's innate immunity and resist microbial invasion. Aggregation-induced luminescence (AIE) is the opposite of aggregation-induced quenching (ACQ). Compounds with AIE properties emit weakly in a dispersed state in solution and they can emit strong fluorescence in an aggregated state. In this article, we proposed a new AIE fluorescent probe QM-ClO based on the quinoline-malononitrile (QM) fluorophore and dimethylthiocarbamate (DMTC) to detect HClO. The probe QM-ClO showed a fast response time, a low detection limit of 30.8 nM and a large Stokes shift (190 nm). Carbonyl cyanide metachlorophenyl-hydrazone (CCCP) was used to induce cell apoptosis, and then an increase in the HClO content was observed in the cell. It is proved that cell apoptosis can lead to the increase of the HClO content in the cell. This probe provides an effective tool for studying apoptosis-related diseases.

Red fluorescent and electrochemical detection of Hg2+ ions using perylene diimide dye: Analysis in soil, urine and water samples

Red (λem =620 nm) fluorescent and electrochemical detection of Hg2+ ions has been achieved in HEPES buffer/DMSO (9/1, v/v, pH = 7.4) using dimethylthiocarbamoyl (DMTC)-functionalized perylene diimide (PDI 2) dye. The self-assembly of PDI 2 showed formation of red-violet non-fluorescent aggregates having spherical microstructures at the interface in >50 % H2O/DMSO mixture supported by optical methods, dynamic light scattering (DLS) studies and atomic force microscopy. The aggregation induced emission (AIE) in PDI 2 transformed into aggregation induced quenching (ACQ) in >30 % H2O/DMSO. Linear correlation ranges for the detection of Hg2+ ions are 0–2 μM and 0–10 nM showed LOD of 8.1 nM and 7.4 nM by absorption and emission-based methods, respectively. The mechanism involves interaction of DMTC with Hg2+ ions however longer incubation time (>24 h) shows chemodosimeter mechanism wherein Hg2+ induced cleavage of DMTC moiety to release PDI-OH. These mechanisms have been supported by NMR/IR studies, model reaction and partially by electrochemical and DLS methods. PDI 2 has been applied for detection of Hg2+ in real water, soil and urine samples with excellent recovery.

An Unexpected 4,5-Diphenyl-2,7-naphthyridine Derivative with Aggregation-Induced Emission and Mechanofluorochromic Properties Obtained from a 3,5-Diphenyl-4H-pyran Derivative.

For a specific fluorescent molecule, the increase of molecular conformation distortion is beneficial to endow it with aggregation-induced emission (AIE) and mechanofluorochromic (MFC) properties. Herein, 3,5-diphenyl-4H-pyran derivative 5 and 4,5-diphenyl-2,7-naphthidine derivative 7 with highly twisted conformations were synthesized. For compound 5, although the introduction of phenyl rings with large steric hindrance at 3 and 5 positions of the 4H-pyran skeleton realized the transformation from aggregation-induced quenching (ACQ)-active molecule to AIE-active molecule, it only showed a low-contrast MFC activity. Compound 7 was accidentally obtained from compound 5 and n-butylamine via a ring-opening and subsequent intramolecular ring-closing mechanism. Compound 7 was confirmed to have a highly twisted molecular conformation by the crystal structural analysis and exhibited AIE activity originated from the restriction of intramolecular rotation. Furthermore, compound 7 exhibited reversible high-contrast MFC activity. Upon grinding, the change of solid-state fluorescence color from orange to yellow was confirmed to be due to the partial destruction of crystal structure. This work provides new ideas for the design and synthesis of novel AIE-active and MFC-active fluorescent molecules based on ACQ-active parent molecules.

ROS and GSH Dual‐Responsive GEM Prodrug Micelles for ROS‐Triggered Fluorescence Turn on Bioimaging and Cancer Therapy

AbstractNanocarriers with minimal drug leakage in blood and sufficient drug release at tumor sites are essential for tumor targeted drug delivery and bioimaging. Herein, a reactive oxygen species (ROS) and glutathione (GSH) dual‐responsive aggregation‐induced quenching (ACQ) prodrug micelle system is developed based on PMPC‐P (Se‐co‐RB)‐P (SS‐GEM) copolymer to avoid drug leakage and specifically locate the tumor via a ROS‐triggered fluorescence turn on manner. Selenium (Se) group is designed to respond to the ROS environment of tumor so as to turn on the fluorescence of Rhodamine B (RB) and Gemcitabine (GEM) is conjugated to the copolymer via a disulfide bond. These GEM prodrug micelles exhibit small particle size of 166.3 nm with uniformed size distribution, a very weak fluorescence emission, and minimal drug release with only 3.33% drug release under physiological conditions after 48 h. However, ROS (0.1% H2O2) and GSH (10 × 10−3 m) could synergistically promote disassembly of the micellar structure which causes accelerated drug release up to around 91.57% after 48 h. These prodrug micelles exhibit great in vitro and in vivo antitumor ability with minimal side effects. This novel drug delivery system provides new possibilities for designing stimuli‐responsive nanocarriers for tumor therapy and bioimaging.

Disulfide bond-based self-crosslinked carbon-dots for turn-on fluorescence imaging of GSH in living cells.

Herein, we report a turn-on fluorimetric nanoprobe for intracellular glutathione (GSH) imaging. The principle of this probe is designed on the basis of the selective reduction between GSH and disulfide bond-based self-crosslinked red emissive carbon dots (abbreviated as SCCDs). The nanoprobe (i.e., SCCDs) was facilely fabricated from thiol-modified carbon dots (CDs) through oxidation in the presence of H2O2, and its fluorescence was greatly reduced due to the effect of aggregation induced quenching (AIQ). However, in the presence of GSH, the SCCDs were separated into many single CDs. As a result, the fluorescence of the nanoprobe was recovered in a GSH concentration-dependent manner, which is the basis for the quantitative analysis of GSH. The nanoprobe shows excellent specificity and a linear range from 0 to 0.15 mM towards GSH with a limit of detection (LOD) of 5.7 μM. Finally, the nanoprobe was demonstrated to have extremely low cytotoxicity, and was successfully applied for monitoring the GSH level in living cells. This work would provide a promising probe for the research of GSH in cytobiology.

Ratiometric detection of alkaline phosphatase based on aggregation-induced emission enhancement.

Alkaline phosphatase (ALP) is an important enzyme that is associated with many human diseases, so the quantitative detection of ALP is vital from a clinical perspective. Nevertheless, most fluorescent assays for monitoring ALP depend on aggregation-induced quenching (ACQ), single-signal modulation, or a "signal off" mode, which suffer from poor sensitivity, a "false positive" problem, and low signal output. In this work, we utilized the electrostatically driven self-assembly of glutathione-capped gold nanoclusters (GSH-AuNCs, which show aggregation-induced emission, AIE) and amino-modified silicon nanoparticles (SiNPs) to create a hybrid probe (SiNPs@GSH-AuNCs). This nanohybrid probe showed emission from the SiNPs at around 470nm as well as aggregation-induced emission enhancement (AIEE) of the GSH-AuNCs at 580nm. The AIEE of the GSH-AuNCs was quenched in the presence of KMnO4, but the AIEE was recovered by adding ascorbic acid as an oxidation-reduction reaction occurred between KMnO4 and the ascorbic acid. The fluorescence of the SiNPs remained constant whether the AIEE was quenched or not, meaning that the fluorescence of the SiNPs could be used as an internal reference. In a typical enzymatic reaction, ascorbic acid 2-phosphate is hydrolyzed by ALP to produce ascorbic acid. Therefore, the hybrid probe was shown to allow the ratiometric detection of ALP, with a linear range of 0.5-10UL-1 and a limit of detection (LOD) of 0.23UL-1. Finally, the proposed analytical strategy was successfully applied to detect ALP in human serum samples and to determine the concentration of an ALP inhibitor. Graphical Abstract.

Mn (II) and Zn (II) complexes of a benzimidazole ligand having undecyl chains: Crystal structures, photophysical and thermal properties

A new tridentate benzimidazole ligand (L‐C11) containing undecyl chains and its Mn (II) and Zn (II) complexes were synthesised and characterized by spectroscopic and analytical methods. Molecular structures of complexes [Mn(L‐C11)Cl2] and [Zn(L‐C11)Cl2] were evaluated by X‐ray diffraction studies. The X‐ray data showed metal ions in both complexes are five‐coordinate with distorted square pyramidal geometry around the metal centres. The undecyl chains in the structure of the complexes are aligned in an interdigitated manner (head to tail) forming a non‐polar domain. The aggregation properties of the ligand and its complexes were investigated by UV–Vis. absorption and emission spectroscopies in DMF‐water mixtures. The emission spectral data revealed that the compounds showed aggregation induced quenching (AIQ) in DMF‐water solutions. Moreover, thermal properties of the compounds were investigated by TG, DTG and DSC analysis.

Nitrogen-doped carbon dots as a ratiometric fluorescent probe for determination of the activity of acid phosphatase, for inhibitor screening, and for intracellular imaging.

The author describe a method for preparation of green fluorescent nitrogen-doped carbon dots (N-CDs) through hydrothermal treatment of a mixture of lotus leaf juice and ethylenediamine (EDA). The N-CDs have uniform size, good dispersibility and water solubility. Under 316 and 366nm photoexcitation, they show dual fluorescence with emission peaks at 415 and 509nm, respectively. They are positively charge and display low cytotoxicity. This makes them an excellent choice for fluorometric assays and for bioimaging. A ratiometric assay was developed for the determination of the activity of acid phosphatase (ACP). It is based on the aggregation- induced quenching (AIQ) of the fluorescence of the N-CDs by sodium hexametaphosphate (NaPO3)6. Enzymatic hydrolysis of (NaPO3)6 by ACP leads to the disintegration of (NaPO3)6 and to the restoration of fluorescence. The measurement of the ratio of fluorescence at two wavelengths (415 and 509nm), background interference and fluctuating signals can be widely eliminated. The method works in the 1-50U·L-1 ACP activity range and has a detection limit of 0.43U·L-1. It was successfully applied (a) to the determination of ACP in spiked serum samples, (b) to ACP inhibitor screening, and (c) to imaging of ACP in HePG2 cells. Graphical abstract Schematic presentation of the synthesis of nitrogen-doped carbon dots (N-CDs), and their application to the ratiometric fluorometric determination of acid phosphatase (ACP) based on the aggregation-induced quenching and enzymatic hydrolysis.

Rational design of cyanovinyl-pyrene dual-emission AIEgens for potential application in dual-channel imaging and ratiometric sensing in living cells

Aggregation-induced emission luminogens (AIEgens) provide a new approach to address the aggregation-induced quenching (ACQ) defect prevalent in traditional fluorescent dyes. Since there are only two dispersion forms of single molecule (monomer state, weak fluorescence) and aggregates (multimer state, strong fluorescence) in aqueous medium, most of the reported AIEgens exhibit a single emission band and therefore cannot be used for dual-channel fluorescence imaging in living cells. In this work, the “monomer-dimer-multimer” dispersion mechanism was innovatively introduced into the design of dual-emission AIEgens. Under the guidance of this concept, two cyanovinyl-pyrene dual-emission AIEgens with twisted molecular configuration have been readily synthesized and studied by theoretical calculations, UV–visible absorption, steady-state fluorescence, time-resolved fluorescence, dynamic laser scanning (DLS) and laser confocal imaging. These AIEgens emit weak fluorescence in monomer state due to intramolecular CC rotation. With gradual aggregation, they form dimer state to emit blue fluorescence centered at 460 nm, and then convert into multimer state to emit red fluorescence around 570 nm, simultaneously exhibiting AIE and dual-emission characteristics. They also have excellent photostability, good membrane permeability and low cytotoxicity. Confocal imaging tests demonstrate that AIEgens composed of cyanovinyl-pyrene and benzimidazole moieties is available for dual-channel imaging in Hela cells and macrophages cells, and shows great potential in designing ratiometric nanoprobe. Our design mechanism will provide a versatile platform for the development of dual-emission AIEgens.

Enhancing the Efficacy of Photodynamic Therapy through a Porphyrin/POSS Alternating Copolymer.

Aggregation-induced quenching (AIQ) of photosensitizers greatly reduces the quantum yield of singlet oxygen generation and mitigates the efficacy of photodynamic therapy (PDT). We have prepared an alternating copolymer starting from 4-vinylbenzyl-terminated tetraphenylporphyrin (VBTPP) and maleimide isobutyl polyhedral oligomeric silsesquioxane (MIPOSS), via alternating reversible addition-fragmentation chain transfer (RAFT) polymerization. Porphyrin and POSS are installed on the amphiphilic block copolymers backbone in an alternating fashion and POSS completely inhibits the aggregation of porphyrin units via stacking. The amphiphilic block copolymer can self-assemble into nanoparticles and its application in PDT treatment was tested. These porphyrin-containing polymeric nanoparticles display high photochemical yield and phototoxicity in vitro and in vivo, providing a novel strategy to enhance the PDT efficacy.

Visible transparent white light emitting ink from a Ce3+ sensitized monodispersed Tb,Sm co-doped LaF3@C-dot nanocomposite.

Bright white light emission (CIE values 0.32 and 0.33) has been achieved by a single excitation source (254 nm) from a monodispersed nanocomposite composed of Ce3+, Tb3+ and Sm3+ doped LaF3 nanocrystals (NCs) and N-doped C-dots where Ce3+ acts as an excellent sensitizer. Controlled deposition of the C-dots onto the surface of the LaF3 NCs impedes conventional aggregation induced quenching (AIQ) of the C-dots in solid state. The transparent colloidal ink was coated onto an UV chip to fabricate a white light emitting diode (WLED) with a luminous efficacy of 8.72 lm W-1.

Carbon-ZnO alternating quantum dot chains: electrostatic adsorption assembly and white light-emitting device application.

Aggregation-induced quenching (ACQ) in carbon nanodots (CNDs) impede their applications in solid devices. Herein, the concept of alternating quantum dot (QD) chains was proposed to overcome the common issue of fluorescence quenching in CNDs; in this study, CNDs and ZnO QDs were interlinked to form carbon-ZnO alternating quantum dot chains (CZA-QDCs), which overcame the ACQ of CNDs and hence ensured efficient full-spectrum fluorescence for white light-emitting devices (WLEDs) without excessive blue emission. Under the excitation of 365 nm lines, white emission resulting from the combination of blue emission from the CNDs and yellow emission from the ZnO QDs has been achieved from these powders. The quantum efficiency of the CZA-QDC powders can reach 49% and remain stable for two months. By coating the powders onto an ultraviolet chip as phosphors, WLEDs with a luminous efficiency of 20.1 lm W-1, color coordinate of (0.30, 0.35), correlated color temperature of 5205 K, and a color rendering index of 84 have been fabricated. Due to the relatively high abundance and eco-friendly characteristics of both carbon and ZnO, the results reported herein may provide a promising alternative to fluorescent phosphors that are widely used in WLEDs.