Preparation and Application of a Sulfur-Doped Fluorescent Carbon Dots with Aggregation-Induced Emission Character.

As a new type of zero-dimensional nanomaterial, carbon dots are widely applied in various fields. However, most of the carbon dots have aggregation fluorescence quenching properties, which limited their practical applications. In this study, a novel sulfur-doped carbon dots (S-CDs) was prepared by solvothermal method. The properties of the S-CDs in ethanol solution and in solid state were investigated respectively. The results showed that the S-CDs have an excited wavelength dependent emission of blue fluorescence in ethanol solution, and have orange fluorescence emission in solid state and composite films, indicating the prepared S-CDs has aggregation-induced emission (AIE) performance. The main reason was that the presence of S-S bonds and the intramolecular rotation of aromatic rings were limited in solid state, resulting in its emission of orange fluorescence. Furthermore, the S-CDs could be applied to identify fingerprints, anti-counterfeiting.

Tetraphenylethene-based mononuclear aggregation-induced emission (AIE)-active mechanofluorochromism gold(I) complexes with different auxiliary ligands.

In this study, a series of tetraphenylethene-containing gold(I) complexes with different auxiliary ligands have been synthesized. These complexes were characterized using a variety of techniques including nuclear magnetic resonance spectroscopy, mass spectrometry, and single crystal X-ray diffraction. Their aggregation-induced emission (AIE) behaviors were investigated through ultraviolet/visible and photoluminescence spectrum analyses, and dynamic light scattering measurements. Meanwhile, their mechanofluorochromic properties were also studied via solid-state photoluminescence spectroscopy. Intriguingly, all these mononuclear gold(I) molecules functionalized by tetraphenylethene group demonstrated AIE phenomena. Furthermore, five gold(I) complexes possessing diverse auxiliary ligands exhibited distinct fluorescence changes in response to mechanical grinding. For luminogens 2-5, their solids showed reversible mechanofluorochromic behaviors triggered by the mutual transformation of crystalline and amorphous states, while for luminogen 1, blue-green-cyan three-color solid fluorescence conversion was realized by sequential mechanical grinding and solvent fumigation. Based on this stimuli-responsive tricolored fluorescence feature of 1, an information encryption system was successfully constructed.

Novel Iminocoumarin-substituted Tetraphenylethylene-based Near-infrared Fluorescent Probe for Ratiometric Detection of F- and H2S.

An iminocoumarin and tetraphenylethylene compound that exhibits aggregation-induced emission (AIE) and a significant Stokes shift (Δλ = 135 nm) in THF was created via the Knoevenagel condensation method. TPICBT could also be used as a ratiometric near-infrared fluorescent probe for the naked color identification of F- and H2S. It showed a large red shift (˃ 90 nm), good selectivity, and anti-interference. Test strip detection and cell imaging had both been accomplished using the probe. In addition, the probe could conveniently detect H2S produced during food spoilage without laboratory instruments.

Rapidly responsive and highly selective NIR fluorescent probe for detecting hydrogen sulfide in food samples and living cells.

Hydrogen sulfide (H2S) is a pungent gas that is one of the key mediators of signal transduction in biological systems, and its presence is related to the freshness of some protein foods. Using phenothiazine derivatives as fluorophores and 2, 4-dinitrobenzene sulfonate (DNBS) fragments as reaction groups, a near-infrared (NIR) probe WX-HS for H2S identification was designed. With the addition of H2S, WX-HS appeared a strong fluorescence signal at 660 nm with short reaction time (90 s) and high sensitivity, and fluorescence state change from non-fluorescent to orange-red. In addition, WX-HS could effectively detect H2S produced during food oxidation. Based on its low cytotoxicity, the WX-HS probe further enabled the detection and imaging of H2S in A549 cells.

A mitochondrial targeted dual ratiometric near-infrared fluorescent probe based on ICT effect for the detection of SO2 derivative and its bioimaging.

SO2 derivatives play an important role in many metabolic processes, excessive ingestion of them can lead to serious complications of various diseases. In this work, a novel dual ratiometric NIR fluorescent probe XT-CHO based on ICT effect was synthesized for detecting SO2 derivative. In the design of the probe, the α, ß-unsaturated bond formed between benzopyran and coumarin was used as the reaction site for SO2, meanwhile, the extended π-conjugate system promoted maximum emission wavelength of the probe up to 708 nm. Notably, the probe exhibited high selectivity and sensitivity for detecting SO2, the limit of detection reached 2.13 nM and 58.5 nM in fluorescence spectra and UV-Vis absorption spectra, respectively. The reaction mechanism of SO2 and XT-CHO had been verified by 1H NMR, ESI-MS spectra and DFT calculation. Moreover, the probe was successfully applied in detecting endogenous and exogenous SO2 in living cells and proved possessed the mitochondrial targeted ability.

Near-infrared fluorescent probe for detection of hydrogen sulfide in water samples and food spoilage.

Hydrogen sulfide (H2S) is a common toxic gas that threatens the quality and safety of environmental water and food. Herein, a new near-infrared fluorescent probe DTCM was synthesized and characterized by single crystal X-ray diffraction for sensing H2S. It exhibited a remarkable "turn-on" near-infrared (NIR) emission response at 665 nm with a remarkably massive Stokes shift of 175 nm, super-rapid detection ability (within 30 s), excellent photostability, high selectivity and sensitivity (limit of detection, LOD = 58 nM). Additionally, the probe was successfully utilized for the detection of H2S in environmental water samples. The DTCM-loaded test papers enabled convenient and real-time monitoring of H2S produced by food spoilage.

Construction of hierarchical porous and polydopamine/salicylaldoxime functionalized zeolitic imidazolate framework-8 via controlled etching for uranium adsorption.

Efficient uranium extraction from seawater is critical for the development of the nuclear industry. Herein, a polydopamine/salicylaldoxime decorated hierarchical zeolitic imidazolate framework-8 (H-PDA/SA-ZIF-8) is constructed by using a controlled etching process. Benefiting from the combination of PDA/SA and the zeolitic imidazolate framework-8 (ZIF-8), as well as a controlled etching process, the H-PDA/SA-ZIF-8 possesses multiaffinity sites, excellent specific surface area (1234.92 m2 g-1), and a hierarchical pore structure. The H-PDA/SA-ZIF-8 exhibits excellent adsorption capacity (Qm = 869.6 mg g-1), selectivity, and reusability in uranium adsorption. The adsorption process of H-PDA/SA-ZIF-8 fits very well with the Langmuir isotherm model and pseudo-second-order models, and the adsorption process equilibrates within 20 min (C0 = 20 mg L-1). Furthermore, the H-PDA/SA-ZIF-8 shows remarkable antibacterial ability. Impressively, the adsorption capacity of H-PDA/SA-ZIF-8 to uranium in natural seawater reaches 6.9 mg g-1 after circulation for 15 days. Therefore, the H-PDA/SA-ZIF-8 is a promising and fascinating material for uranium extraction from natural seawater.

Mechanistic insights into diversified photoluminescence behaviours of BF2 complexes of N-benzoyl 2-aminobenzothiazoles.

Many BF2 complexes of heteroaromatics are well known for their dual-state emission (DSE) properties. However, AIE and ACQ effects have also been observed in certain cases. To date, no rational explanations have been proposed for these uncommon photoluminescence (PL) behaviours. The current research prepared four BF2 complexes of N-benzoyl 2-aminobenzothiazoles with diversified photoluminescence (PL) properties as model compounds and utilized quantum chemical calculation tools to address this issue. Theoretical calculations revealed that the electron-donating groups (EDGs) at the para-position of the exocyclic phenyl ring exert significant influence on their ground-state electronic structures and vertical excitation features. Potential energy curve (PEC) analysis showed that the exocyclic phenyl ring and NMe2 could not function as effective rotors due to elevated energy barriers. Only the NPh2 of BFBB-3 could spontaneously rotate ∼60° to induce the formation of an emissive twisted intramolecular charge transfer (TICT) state. The two-channel model involving both vibronic relaxation and S0/S1 surface crossing revealed that the drastic narrowing of the S1/S0 energy gap in the region approaching minimun energy conical intersection (MECI) led to the generation of a dark state in BFBB-1. The small energy barrier to access the dark-state region makes the resulting fast internal conversion a competitive channel for excited-state deactivation. In contrast, the presence of EDGs in BFBB-2 and 4 inhibits this pathway, thereby resulting in intense fluorescence emissions in solution. In addition, crystallographic analysis illustrated that the F atoms perpendicular to the polyheterocycle promoted a slipped face-to-face packing mode and enhanced intermolecular interactions. The efficiencies of their solid-state emissions are mainly affected by the degree of π-π overlaps.

A turn-on fluorescence probe for imaging tyrosinase at the wound site in broken tail of zebrafish.

Tyrosinase (TYR) is a copper-containing oxidase that affects the synthesis of melanin in the human body, which is regulate to the pigmentation of the skin. Nevertheless, abnormal expression of TYR can lead to albinism, vitiligo and other skin diseases. Excessive accumulation of TYR is a marker of melanoma cancer and an important factor leading to pigmentation during wound healing, freckles and browning of fruits and vegetables. Efficient tracking of TYR is of significance for studying its pathophysiological mechanism. Herein, we synthesized a benzindole-based fluorescent probe Pro-OH to detect TYR in living cells and zebrafish. The probe displayed a high selectivity and sensitivity in distinguishing TYR from other analytes with the low detection limit of 1.024 U/mL. Importantly, Pro-OH was successfully used to imagine TYR at the wound site of broken tail of zebrafish.

Construction of a Reversible Solid-state Fluorescence Switching Via Photochromic Diarylethene and Si-ZnO Quantum Dots.

Developing fluorescence switching as functional system is highly desirable for potential applications in the fields of light-responsive materials or devices. Attempt to construct fluorescence switching system tend to focus on the high fluorescence modulation efficiency, especially in solid state. Herein, a photo-controlled fluorescence switching system was constructed with photochromic diarylethene and trimethoxysilane modified zinc oxide quantum dots (Si-ZnO QDs) successfully. It was verified by the measurement of modulation efficiency, fatigue resistance as well as theoretical calculation. Upon irradiation with UV/Vis lights, the system exhibited excellent photochromic property and photo-controlled fluorescence switching performance. Furthermore, the excellent fluorescence switching characters could also be realized in solid state and the fluorescence modulation efficiency was determined to be 87.4%. The results will provide new strategies to the construction of reversible solid-state photo-controlled fluorescence switching for the application in the fields of optical data storage and security labels.

Hierarchical Porous Amidoximated Metal-Organic Framework for Highly Efficient Uranium Extraction.

With the rapid development of industry and technology, high-efficiency extraction of uranium from seawater is a research hotspot from the aspect of nuclear energy development. Herein, a new amidoximated metal-organic framework (UiO-66-DAMN-AO) constructed through a novel organic ligand of 2-diaminomaleonitrile-terephthalic acid (BDC-DAMN) is designed via one-step post-synthetic methods (PSM), which possess the merit of abundant multiaffinity sites, large specific surface area, and unique porous structure for efficient uranium extraction. Adopting one-step PSM can alleviate the destruction of structural stability and the reduction of the conversion rate of amidoxime groups. Meanwhile, introducing the BDC-DAMN ligand with abundant multiaffinity sites endow UiO-66-DAMN-AO with excellent adsorption ability (Qm = 426.3 mg g-1) and selectivity. Interestingly, the UiO-66-DAMN-AO has both micropores and mesopores, which may be attributed to the partial etching of UiO-66-DAMN-AO during the amidoximation. The presence of mesopores improves the mass transfer rate of UiO-66-DAMN-AO and provides more exposed active sites, favoring the adsorption of uranium on UiO-66-DAMN-AO. Thus, this study provides a feasible strategy for modifying metal-organic framework (MOFs) with plentiful amidoxime groups and the promising prospect for MOF-based materials to adsorb uranium from ocean.

High-contrast multicolour photoswitching based on dithienylethene Schiff base with a hydrazinylquinoline moiety.

A new asymmetrical photochromic diarylethene DTE-HQo composed of a 2-hydrazinoquinoline moiety as the binding unit for ions and dithenylethene as a photoswitching trigger was reported. DTE-HQo displayed favourable photochromism upon irradiation with UV/vis light. Its fluorescent behaviour could be efficiently modulated by light, Zn2+, Cd2+ and HSO4-. The binding of Zn2+ induced a strong fluorescence peak at 510 nm in DTE-HQo due to the formation of a 1:2 complex [Zn2+ + 2DTE-HQo], resulting in a notable colour change from dark to intense white emission. Triggered by Cd2+, DTE-HQo formed a 1:1 complex [Cd2+ + DTE-HQo], leading to an enhanced emission intensity by 21-fold with an emission peak red-shifted from 461 nm to 514 nm. Unexpectedly, [Zn2+ + 2DTE-HQo] underwent hydrolysis when stimulated with water, generating a yellow-emitting complex [Zn2+ + DTE-HQo]. This color change easily distinguishes it from Cd2+ complex. Additionally, DTE-HQo showed high selectivity towards HSO4- and exhibited distinct "turn-on" fluorescence with a colour change from dark to bright blue upon stimulation. Moreover, the strong emission complexes of DTE-HQo with Zn2+, Cd2+ and HSO4- could be effectively quenched during the photocyclization process. Therefore, DTE-HQo can serve as an unimolecular multicolour photoswitching chemosensor, offering potential applications as a multifunctional probe for detecting Zn2+, Cd2+ and HSO4-.

Development of europium(III) complex fluorescent probe for hydrogen sulfide detection and its application in water samples.

Hydrogen sulfide (H2 S) is a crucial endogenous signaling component in organisms that is involved in redox homeostasis and numerous biological processes. Modern medical research has confirmed that hydrogen sulfide plays an important role in the pathogenesis of many diseases. Herein, a fluorescent probe Eu(ttbd)3 abt based on europium(III) complex was designed and synthesized for the detection of H2 S. Eu(ttbd)3 abt exhibited significant quenching for H2 S at long emission wavelength (625 nm), with rapid detection ability (less than 2 min), high sensitivity [limit of detection (LOD) = 0.41 µM], and massive Stokes shift (300 nm). Additionally, this probe showed superior selectivity for H2 S despite the presence of other possible interference species such as biothiols. Furthermore, the probe Eu(ttbd)3 abt was successfully applied to detect H2 S in water samples.

A dual-response NIR fluorescent probe for separately and continuously recognizing H2S and Cys with different fluorescence signals and its applications.

Given the significant interactions between hydrogen sulfide (H2S) and cysteine (Cys) in organisms, a dual-site multi-purpose fluorescent probe (Cy-NP) for H2S and Cys was synthesized. Cy-NP is composed of two fluorophores: naphthalimide that emits in the visible region of 500-600 nm, and cyanine dye that emits in the NIR region of 700-800 nm. Cy-NP showed admirable sensitivity and selectivity for identifying H2S and Cys by fluorescent signals with limits of detection as low as 0.15 µM and 1.4 µM, respectively. Furthermore, other biological thiols (especially GSH and Hcy) showed no positive response to Cy-NP compared with H2S and Cys. The chemical mechanism of Cy-NP with H2S and Cys in DMF/PBS (1/1, v/v, pH = 7.4) solution was verified by HRMS and DFT calculations. Further, Cy-NP was successfully applied to monitor H2S released in raw meat and adapted to detect H2S and Cys in MCF-7 cells independently and continuously.

A photo-controlled fluorescent switching based on carbon dots and photochromic diarylethene for bioimaging.

Carbon dots (CDs) as luminescent zero-dimensional carbon nanomaterials have good aqueous dissolution, photostability, high quantum yield, and tunability of emission color. It has great application potential in many fields, including bioimaging, labeling of biological species, drug delivery, and sensing in biomedical. However, controlling the fluorescence emission of carbon dots remains a formidable challenge. Herein, we designed and exploited a photo-controlled fluorescent switching based on photochromic diarylethene (DT) and CDs for bioimaging. It could be modulated reversibly between "ON" and "OFF" under UV/vis light exposure. The fluorescent modulation efficiency was as high as 95.3%. The fluorescent switching could be used to the bioimaging in HeLa cells with low cell toxicity. Therefore, this fluorescent switching could be a promising candidate in many potential application areas, especially in bioimaging.

A novel diarylethene-based fluorescence sensor for Zn2+ detection and its application.

A series of fluorometric sensors of Zn2+ have been synthesized due to the significant function of Zn2+ in the human body and environment. However, most of probes reported for detecting Zn2+ have high detection limit or low sensitivity. In this paper, an original Zn2+ sensor, namely 1o, was synthesized by diarylethene and 2-aminobenzamide. When Zn2+ was added, the fluorescence intensity of 1o increased by 11 times within 10 s, along with a fluorescence color change from dark to bright blue, and the detection limit (LOD) was calculated to be 0.329 µM. According to Job's plot curves, the binding mode of 1o and Zn2+ was measured as 1:1, which was further proved by 1H NMR spectra, HRMS and FT-IR spectra. The logic circuit was designed to take advantage of the fact that the fluorescence intensity of 1o can be controlled by Zn2+, EDTA, UV and Vis. In addition, Zn2+ in actual water samples were tested, in which the recovery rate of Zn2+ was between 96.5 % and 109 %. Furthermore, 1o was successfully made into a fluorescent test strip, which could be used to detect Zn2+ in the environment economically and conveniently.

A "Turn-on" Fluorescent Probe Based on Phenothiazine for Selectively Recognizing ClO- and its Practical Applications.

Hypochlorous acid (HClO), a highly reactive oxygen species, has important effects on human health. High selectivity and sensitivity remain challenges of fluorescent probes for detection of ClO- with a large Stokes shift. This work designed and synthesized a novel phenothiazine-based fluorescent probe TF which can detect ClO- by colorimetric and fluorescent dual signals. TF displayed turn-on fluorescence effect toward ClO- with high selectivity (≥ 28-folds) and sensitivity (LOD = 0.472 µM), fast response time (< 1 min) and large Stokes shift (150 nm) in PBS (pH = 7.4, 40% DMSO). Meanwhile, TF can visualize ClO- on the mung bean sprouts model and apply as testing strips for portable and rapid detecting ClO- by the naked eyes. A phenothiazine-based fluorescent probe with large Stokes shift was synthesized and its responding rapidly ability to detect ClO- was studied.

A Handy Chemical Sensor Based on Benzaldehyde and Imidazo[1,2-a]pyridine Mixture for Naked-eye Colorimetric and Fluorescent Detection of F.

Upon the Schiff base condensation reaction of imidazo[1,2-a]pyridine-2-carbohydrazide and 2,5-dihydroxybenzaldehyde, a bimodal colorimetric and fluorescent chemosensor 1o for assaying fluoride (F-) in DMSO was synthesized. The characterization of 1o structure was obtained by 1H NMR, 13C NMR and MS.The structure of 1o was characterized by 1H NMR, 13C NMR and MS. Under the presence of various anions, 1o could be applied for naked-eye and fluorescent detection of F- (naked eye: colorless to yellow; fluorescence: dark to green) and displayed promising performance, such as high selectivity and sensitivity, as well as a low detection limit. Upon calculation, the detection limit of chemosensor 1o for F- was 193.5 nM, which is well below the allowed maximum value of F- (1.5 mg/L) by WHO. As the intermolecular proton transfer mechanism induced "turn-on" fluorescent signal and naked-eye color change of F- to 1o through deprotonation effect, which was confirmed by Job's plot curve, mass spectrometry and 1H NMR titration. Alternatively, the chemosensor 1o can be effectively manufactured into test strips to detect fluoride in solid state, which is user-friendly with no additional equipment required.

In situ generated PANI promoted flexible photoelectrochemical biosensor for ochratoxin A based on GOx-stuffed DNA hydrogel as enhancer.

A flexible photoelectrochemical (PEC) biosensor is proposed for the sensitive detection of ochratoxin A (OTA) based on glucose oxidase (GOx)-encapsulated target-responsive hydrogel, using Fenton reaction-mediated in situ formation of polyaniline (PANI) as signal amplified strategy. The target-responsive DNA hydrogels with high loading capacity can carry a large amount of GOx, which not only avoids laborious labeling process but also enhances the analytical performance. Upon introduction of target molecules, the hydrogel can be opened, and multiple GOx was released, thus producing lots of H2O2 via catalytic reduction of glucose. As a component of the Fenton reagent, H2O2 can react with the Fe2+ on the graphene oxidase-PAMAM-Fe2+ (GO-PAMAM-Fe2+) to generate Fe3+ and ·OH. This in turn can oxidize aniline and generate polyaniline (PANI), resulting in the enhancement of the photocurrent signal of GO-MoS2-CdS photoelectrode. The GO-PAMAM-Fe2+ as the neighborhood component of GO-MoS2-CdS-based photoactive material not only can increase the loading amount of Fe2+, but also can inhibit the decrease of photocurrent of GO-MoS2-CdS by direct modification of Fe2+ on the photoactive material. Moreover, the high loading capacity of DNA hydrogel can efficiently promote the performance of the PEC biosensor. The PEC biosensor exhibited satisfactory analytical performance for OTA with a linear range of 0.0001-0.1 ng/mL and a low detection limit of 0.05 pg/mL. It presents recommendable specificity, stability, and practical applications. Importantly, the PEC biosensor provides a new concept for construction of PEC biosensing platform.

Mitochondria-targeted fluorescent probe with long wavelength emission for detecting H2S and its application in foodstuff, water and living cells.

Hydrogen sulfide (H2S) is crucial to cellular energy production, apoptosis, and redox homeostasis in mitochondria of living cells. In this work, a unique mitochondria-targeting fluorescence probe (DDMI) was established for H2S determination based on styrylpyridinium scaffold. When DDMI was treated with H2S, it showed significant fluorescence enhancement at 623 nm, with good selectivity, and high sensitivity. In addition, the "turn-on" fluorescent probe DDMI could detect H2S in water samples with good recoveries in the range of 95.4 %-105.6 % and track the degree of food spoilage by visualizing the change of DDMI-loaded test strips. Furthermore, the established probe DDMI was successfully used for monitoring exogenous H2S in living cells and mitochondria targeting. These results paved the way for success in developing a technology that could be used to identify H2S in environment, foodstuff, and living cells.