A simple, one-pot method for the synthesis of seven novel dihydrothiazole-hydrazone compounds is presented, employing a condensation-cyclization protocol, with the products characterized by FTIR, [1]H NMR, [13]C NMR, and ESI-MS. Thiazoles and hydrazones are distinguished by versatile chelating properties and fluorescent conjugated scaffolds, and their combination can be considered a promising route to obtaining tunable fluorophores. According to the UV-Vis absorption and fluorescence data, all seven compounds demonstrated absorption maxima at 412-420 nm and emitted a yellow-green light at 554-575 nm. The substituent present at the C-4 position of the dihydrothiazole ring governed the emission wavelength and intensity. Electron-donating groups increased emission intensity and shifted the emission to longer wavelengths, whereas electron-withdrawing groups quenched fluorescence, likely via a photoinduced electron transfer (PET) deactivation mechanism. The Stokes shifts (142-155 nm) also followed the same substituent-dependent pattern. Moderate fluorescence quantum yields (1.64-5.54%) were observed for the thiazoles, indicating that the presence of different functional groups influenced the efficiency of excited-state relaxation. The way substitution influences absorption and emission behavior establishes the dihydrothiazole-hydrazone core as a versatile unit that can be tuned to serve as a fluorophore for sensing, biological, and optoelectronic applications.

Fluorescent liquid crystal displays (FLCDs) developed through adding fluorescent dye molecules into the liquid crystal (LC) hosts to enhance optical efficiency and brightness of the displays, have become promising in contrast to the traditional liquid crystal displays (LCDs). The basic principles, materials and new technological advances in FLCD systems are discussed in the present review. The principle of operation of FLCDs under an applied electric field relies on the electro-optical (E-O) switching of LC molecules, which concurrently allows directing scaffold-based fluorescent dyes and regulating fluorescence intensity, polarization and color. Common FLCD architectures are based on nematic LC (NLC) hosts like E7 or 5CB(4-pentyl-4'-cyanobiphenyl), fluorescent dyes like perylene, coumarin, rhodamine and anthracene analogs, transparent indium tin oxide (ITO) electrodes and polyimide (PI) alignment layers. Several technologies like dye doped LC systems, guest host FLCDs, photo responsive and optically switchable displays, polarized fluorescent LC materials and electrically switchable fluorescent devices have shown critical advancements in brightness, contrast ratio (CR), response time and color purity. The color gamut of a conventional LC display (LCD) system has also been extended using advanced fluorescent backlight technologies based on quantum dots (QDs) and perovskite nanomaterials. In spite of these advancements, dye aggregation, photobleaching, fluorescence quenching and long-term stability are some of the challenges that are of great concern. Continued research on novel fluorescent materials, nanostructured dopants and optimized device architectures is expected to enable high efficiency, low power and next generation fluorescent LCD technologies.

Luminescence resonance energy transfer (LRET) serves as the fundamental principle for constructing probes based on lanthanide-doped upconversion nanoparticles (UCNPs). The signal contrast of a UCNP-based probe is determined by the LRET efficiency, which directly limits the maximum signal-to-background ratio (SBR) and the limit of detection (LOD). To enhance the SBR, we developed a dye-sensitized upconversion nanoparticle, denoted as UCNPs@IR780, in which the upconversion luminescence (UCL) is efficiently quenched by LRET acceptors. The dye-sensitized upconversion emission originates from the UCNPs but is enhanced through dye-sensitization by the organic dye IR780. In addition to quenching the luminescence of UCNPs, simultaneous quenching of IR780 further suppressed the UCL, thereby improving the SBR. We employed MnO2 nanosheets as LRET acceptors, achieving a quenching efficiency of up to 90.8% for UCNPs@IR780. Upon interaction with glutathione (GSH), a molecule involved in numerous physiological processes, the MnO2 nanosheets were degraded, leading to recovery of the UCL signal. The system achieves a maximum SBR of 9.3 and an LOD of 0.1 µM for GSH. The improved SBR and LOD demonstrate that the dye-sensitized strategy effectively overcomes the inherent SBR limitations of conventional UCNP-based probes, thereby broadening their applicability in biosensing applications.

During propellant storage, the release of nitrogen oxides consumes the stabilizer 2-nitrodiphenylamine (2-NDPA), whose residual content serves as a key indicator for assessing ammunition aging and safe service life. Conventional detection methods, predominantly based on chromatography, are hindered by high costs, complex operation, and unsuitability for on-site analysis. Herein, we report a rapid detection method using coumarin 153 (C153) as a single fluorescent signal unit. Experimental results show that the fluorescence intensity of C153 at 527 nm decreases linearly upon addition of 2-NDPA, with a rapid response (response time < 5 s) and a detection limit of 0.60 µmol·L[-1]. Selectivity tests against 19 structurally analogous stabilizers and their derivatives confirm the high specificity of this probe for 2-NDPA. Mechanistic investigations, combining fluorescence lifetime measurements and spectral overlap analysis, attribute the quenching to the inner filter effect. Furthermore, the practical utility of this method is validated through both leachate and vapor-phase tests on aged propellant samples, demonstrating that the fluorescence quenching response correlates inversely with the extent of aging. This strategy offers a cost-effective and operationally simple alternative for monitoring propellant stabilizers.

Simultaneous monitoring of environmental polarity and cysteine (Cys) is of considerable importance for understanding cellular microenvironments and disease-associated physiological processes. However, fluorescent probes capable of dual-responsive sensing toward both polarity and Cys remain rarely reported. Herein, Mn-engineered tryptophan-derived carbon dots (Mn-TrpCDs) were successfully synthesized using MnCl2 and D-tryptophan as precursors. Structural characterization demonstrated that Mn atoms were atomically dispersed and stabilized within the carbon framework through N/O coordination, resulting in carbon dots with uniform particle size, moderate graphitization, and abundant surface functional groups. Under excitation at 373 nm, Mn-TrpCDs exhibited strong blue fluorescence centered at 452 nm and displayed distinct dual fluorescence responses toward both environmental polarity and Cys. The fluorescence intensity increased progressively with increasing solvent polarity and showed an excellent linear response toward Cys over the concentration range of 0-80 µM, with a limit of detection (LOD) of 0.31 µM. In addition, the probe reached a stable fluorescence response within 10 min and exhibited excellent salt tolerance, broad pH adaptability, outstanding photostability, and high selectivity toward Cys over various potential interferents. Furthermore, owing to its low cytotoxicity and favorable biocompatibility, Mn-TrpCDs enabled fluorescence imaging of intracellular Cys in HK-2 cells. To the best of our knowledge, this is the first report of Mn-engineered carbon dots as a dual-responsive fluorescent probe for the simultaneous sensing of environmental polarity and Cys. This work provides a simple strategy for constructing multifunctional Mn-Engineered carbon-dot fluorescent probes and expands their potential applications in fluorescence sensing and bioimaging.

Upconverting nanoparticles (UCNPs) composed of sodium yttrium fluoride (NaYF4) nanocrystals doped with trivalent rare-earth ions are synthesized by a co-precipitation method. Under 980 nm excitation, the UCNPs exhibit two prominent emission bands, both of which undergo significant quenching upon introduction of lycopene. Laser-induced fluorescence measurements reveal a pronounced decrease in luminescence intensity following lycopene addition. UV-visible absorption and steady-state fluorescence spectroscopy further demonstrate a linear correlation between lycopene concentration and signal attenuation. The limit of detection (LOD) for the UV-Vis assay is 328 ppm, while fluorescence detection attains an LOD of 234.5 ppm. Correlation coefficients (R[2]) of 0.9931 (UV-Vis) and 0.9958 (fluorescence) and relative standard deviations (RSD) of 3.9% and 1.76%, respectively, indicate high analytical performance. Quenching behavior is rationalized in terms of energy transfer mechanisms, underscoring the potential of UCNP-lycopene systems for optical sensing applications.

Copper ions (Cu[2+]) play important roles in crop growth and agricultural production, but excessive Cu[2+] accumulation in crops and their growth environments may pose risks to crop quality, food safety, and human health. In view of increasing copper contamination in agricultural environments, developing rapid, sensitive, and reliable methods for Cu[2+] determination in real agricultural matrices is highly desirable. In this work, a high-affinity near-infrared (NIR) fluorescent probe, DCI-Cu, was successfully developed for interference-resistant Cu[2+] determination. The probe exhibited NIR emission at 670 nm, a large Stokes shift of approximately 200 nm, broad pH tolerance, favorable photostability, high selectivity, and strong anti-interference capability toward common coexisting species, especially sulfur-containing species, biological thiols, and ethylenediaminetetraacetic acid (EDTA). Benefiting from these properties, DCI-Cu enabled ultrafast and sensitive Cu[2+] detection with a fluorescence "turn-off" response within 3 s and a low detection limit of 136 nM. Mechanistic studies supported a 1:1 binding model between DCI-Cu and Cu[2+], and the high coordination constant of 8.42 × 10[7] M[-1] was associated with a proposed six-coordinate coordination model. DCI-Cu was successfully applied to accurate quantitative detection of Cu[2+] in real water, soil, and crop samples, with satisfactory recoveries of 96.5%-105.5% and low RSDs of 1.43%-2.51%. Moreover, DCI-Cu was successfully used for in situ fluorescence imaging of Cu[2+]-related changes in living triticale leaves. Consequently, DCI-Cu provides a promising NIR fluorescence tool for rapid, sensitive, and interference-resistant Cu[2+] analysis in crop-associated environmental and plant matrices.

Matrix metalloproteinase-3 (MMP-3) is a critical biomarker for inflammatory responses and tissue remodeling following joint surgery. Here, we developed a ratiometric fluorescence probe based on fluorescence resonance energy transfer (FRET) for sensitive and selective detection of MMP-3 activity. The probe comprises CdTe quantum dots (R-QDs) as the energy donor and BHQ as the acceptor, linked by an MMP-3-cleavable peptide. Upon MMP-3 cleavage, the FRET process is disrupted, resulting in fluorescence recovery at 540 nm, while the reference signal at 690 nm remains constant, enabling ratiometric quantification. The probe exhibits a linear response from 20 to 100 nM with a detection limit of 7.8 nM and excellent selectivity against other MMPs and interfering proteins. Clinical validation using serum samples from 11 subjects (5 healthy controls and 6 post-surgery patients) successfully distinguished patients from controls. Moreover, real-time monitoring of 6 patients over 18 days post-surgery revealed a clear correlation between MMP-3 levels and rehabilitation progress. These results demonstrate that our ratiometric FRET probe holds promise for postoperative rehabilitation assessment and prognostic monitoring following joint surgery.

Developing an Aggregation-Induced Emission Enhancement (AIEE) type probe with enhanced emission through metal ion-induced methods has been a significant challenge. In this work, we synthesized an AIEE fluorescent chemosensor P1 via a Schiff base reaction by 8-hydroxyquinoline-2-carbaldehyde and 2,4-difluorophenylhydrazine. Experimental results demonstrate that chemosensor P1 exhibits AIEE behavior in DMSO/glycerol mixed solvents. Significantly, this probe exhibits multifunctionality in ethanol solution: (1) specific recognition of Zn[2+]/Cd[2+] ions against other cations; (2) colorimetric discrimination of concentration-dependent under white light; (3) metal ion-triggered red luminescence observed in the solution is similar to the characteristic emission signatures of the excited-state intramolecular proton transfer (ESIPT)-driven molecules in methanol. The system demonstrates good linear relationships between fluorescence intensity and ion concentration within specific ranges in ethanol: For Cd[2+]: 4.0 × 10[-7]-2.2 × 10[-6] mol·L[-1] with a detection limit of 9.11 × 10[-8] mol·L[-1]; For Zn[2+]: 2.0 × 10[-7]-2.0 × 10[-6] mol·L[-1] with a detection limit of 1.02 × 10[-7] mol·L[-1]. Thus, chemosensor P1 is capable of detecting both Cd[2+] and Zn[2+] with significant red fluorescence enhancement, which establishes a new strategy for designing ESIPT Schiff-base probes.

Amyloid-β42 (Aβ42) is an important pathological biomarker associated with the development and progression of Alzheimer's disease (AD). Differentiating Aβ42 species with distinct aggregation states is therefore relevant for investigating disease-associated aggregation and developing fluorescence-based sensing strategies. In this study, biocompatible EGCG@Zn fluorescent nanocomplexes were prepared through a facile coordination-driven self-assembly approach under different pH conditions and evaluated for Aβ42 detection. The nanocomplexes were characterized by fluorescence spectroscopy, FE-SEM, EDX, TEM, DLS, XRD, FTIR, and XPS, confirming Zn[2+] incorporation into the EGCG framework and the formation of nanoscale metal-phenolic assemblies with distinct morphological, structural, and surface-chemical characteristics. Their fluorescence behavior was strongly dependent on the synthesis pH, with the nanocomplex prepared at pH 7.3 exhibiting the highest intrinsic fluorescence and the most balanced analytical performance. The optimized nanocomplex produced concentration-dependent and distinguishable fluorescence responses toward the prepared oligomer-enriched and fibril-enriched Aβ42 fractions. The calculated limits of detection were 9.03 × 10[-12] mg mL[-1] for the oligomer-enriched fraction and 8.02 × 10[-12] mg mL[-1] for the fibril-enriched fraction, with corresponding limits of quantification of approximately 6.3 × 10[-11] and 3.9 × 10[-11] mg mL[-1], respectively. In vitro evaluation using PC12 cells further demonstrated low cytotoxicity and good biocompatibility over the investigated concentration range. Overall, the self-assembled EGCG@Zn nanocomplexes provide a simple, biocompatible, and responsive fluorescent platform for proof-of-concept sensing of Aβ42 aggregate-enriched fractions, with potential for further development in Alzheimer's disease biomarker analysis.

Contamination by the heavy metal cobalt ion (Co[2+]) poses a serious threat to the ecological environment and human safety. Consequently, there is an urgent need to develop a new method for detecting Co[2+] that combines rapid response, high sensitivity and high selectivity. In this study, carbon dots (CDs) were prepared using urea and citric acid as raw materials. These were mixed with MOF-Eu and incorporated into a PA hydrogel constructed from sodium alginate (SA) and acrylamide (PAM), resulting in the successful preparation of a PA-CDs@MOF-Eu composite hydrogel with dual-wavelength independent luminescence properties. The results indicate that the hydrogel exhibits characteristic red fluorescence from MOF-Eu upon excitation at 398 nm and characteristic blue fluorescence from CDs upon excitation at 342 nm; precise control of the dual wavelengths can be achieved by adjusting the excitation wavelength. Furthermore, the hydrogel enables highly sensitive and selective visual detection of Co[2+], with a detection limit (LOD) of 0.22 µM within a linear response range of 0 ~ 120 µM. The fluorescence quenching mechanism of the hydrogel upon introduction of Co[2+] is attributed to electronic energy transfer (EET). This study provides a new, highly efficient and stable material for the detection of heavy metal ions, offering significant potential for application in fields such as water quality testing and environmental monitoring.

Rare earth ions, owing to their unique electronic structures, have important applications in luminescent materials. Among them, Dy(III) complexes have attracted considerable attention for their characteristic blue and yellow emissions. In this work, two Dy(III) coordination polymers (CPs) were synthesized by reacting Dy(ClO4)3 with two different aromatic dicarboxylate ligands under hydrothermal conditions at 170 °C. Single-crystal X-ray structure determination reveals that the chemical formulas of the two CPs are {[Dy2(5-OH-1,3-bdc)(1,2-bdc)2(H2O)2]·2 H2O}n (CP-1) and [Dy(1,4-bdc)0.5(1,2-bdc)(H2O)2]n (CP-2) (5-OH-1,3-H2bdc = 5-hydroxy-1,3-benzenedicarboxylic acid; 1,2-H2bdc = 1,2-benzenedicarboxylic acid; 1,4-H2bdc = 1,4-benzenedicarboxylic acid). In CP-1, the 5-OH-1,3-bdc and 1,2-bdc ligands coordinate with Dy(III) to form a two-dimensional (2D) layered structure, whereas in CP-2, the 1,4-bdc and 1,2-bdc ligands construct a three-dimensional (3D) framework. Both CPs exhibit the characteristic Dy(III) fluorescence upon ultraviolet (UV) excitation. The luminescence lifetimes of CP-1 and CP-2 are 5.157 µs and 3.336 µs, respectively, and a qualitative analysis of the difference between them was performed.

Viscosity is a key parameter for the quality of liquid foods and is also closely related to the occurrence of various diseases in biological systems. Therefore, real-time monitoring of microviscosity changes in food and intracellular is of great significance. In this paper, a near-infrared viscosity probe (CDM) was exploited, which enables highly specific and sensitive monitoring of viscosity changes in food and intracellular environments. The CDM exhibits a 27-fold enhancement in fluorescence intensity under high-viscosity conditions, demonstrating excellent sensitivity and selectivity, along with superior photostability and biocompatibility. Probe CDM was applied to monitor the viscosity changes induced by Nystatin and Momantin in liver cancer cells and effectively monitored the dynamic changes of intracellular viscosity in APAP-induced liver injury. Furthermore, this probe has successfully measured the viscosity changes of two different juices during spoilage. These research results indicate that CDM can serve as a novel analytical method for monitoring the viscosity changes of beverage spoilage during the spoilage process, and also as a reliable tool for early diagnosis of liver diseases and exploration of their underlying pathogenesis.

A novel dual-emission ratiometric fluorescent sensor, Dye@Tb-MOFs, was successfully constructed via a simple post-synthetic method. Using an excitation wavelength of 320 nm, the resulting composite exhibits dual well-resolved emission bands at 440 nm (attributed to the dye) and 545 nm (characteristic of Tb[3+] ions), with the fluorescence intensity ratio (I545/I440) serving as a self-calibrating signal. The sensor demonstrates excellent stability over a wide pH range (3-9) and outstanding selectivity for uric acid (UA) in the presence of common urinary components. Upon interaction with UA, the green emission at 545 nm is selectively and significantly quenched, whereas the blue emission at 440 nm remained almost unchanged. As a result, I545/I440 shows a significant reduction, accompanied by a visually discernible fluorescence color change of the test strips under UV light from the original green to blue. A good linear relationship between the ratiometric signal and UA concentration is established in the range of 10-1000 µM, with a detection limit as low as 1.70 µM. In addition, the sensor exhibits satisfactory reusability. The quenching mechanism was attributed to the competitive absorption of excitation energy between the ligand and UA, following the inner filter effect principle. This work presents a highly selective and sensitive ratiometric fluorescent platform for the direct UA detection, showing great potential for biosensing applications.

The present study focuses computational design and theoretical evaluation of ten different donor-π-acceptor (D-π-A) organic dyes F (1-10), for dye-sensitized solar cell (DSSC) applications. The dye molecules are incorporated using 4-methyl-4H-dithieno[3,2-b:2',3'-d]pyrrole π-bridge combined with different electron-donating groups, including amino, dimethylamine, methoxy, and diphenylamine, along with electron-withdrawing acceptors such as nitro (-NO2), cyano (-CN), cyanoacrylic acid (CAA), 4,5-dicyanoimidazole (DCI), and 5,6-dicyanobenzoimidazole (DCBI). Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been performed to investigate the electronic, optical, and photovoltaic properties. The optimized dyes exhibit narrow energy gaps (2.67- 4.00 eV) and strong intramolecular charge-transfer (ICT) characteristics with absorption maxima ranging from 312.5 nm to 564.3 nm. Organic dyes with CAA, DCI and DCBI units significantly enhance ICT strength, red-shifts absorption spectra, and improve electron injection efficiency. The calculated open-circuit voltages ([Formula: see text]) span from 1.18 V to 1.41 V, while light-harvesting efficiencies (LHE) reach up to 96.57%. The photovoltaic analysis shows outstanding device performance, with short-circuit current densities ([Formula: see text]) reaching 32.3 mA cm[-][2] and power conversion efficiencies (PCE) up to 37.8%. Collectively, these results underscore the potential of the proposed dyes as high-efficiency sensitizers for next-generation DSSC applications.