2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) is a chlorophenoxy herbicide of environmental concern due to its persistence, toxicity, and potential ecological and human health risks. The development of rapid, sensitive, and environmentally friendly analytical methods for its determination remains an important challenge. The novelty of this work lies in the use of a hexadecyltrimethylammonium bromide (HTAB)-stabilized silver nanoparticle (AgNP) fluorescence system as a simple analytical platform for the determination of 2,4,5-T in environmental water samples, combining minimal sample treatment with satisfactory analytical performance. The synthesized nanoparticles were characterized by scanning electron microscopy (SEM), dynamic light scattering (DLS), UV–Vis absorption spectroscopy, and fluorescence spectroscopy. Experimental variables affecting the analytical response were systematically optimized, and the method was evaluated in environmental and tap water samples. Under the optimized experimental conditions, the addition of 2,4,5-T to the AgNPs–HTAB system produced a reproducible increase in fluorescence intensity at 365 nm using an excitation wavelength of 300 nm. The complete calibration dataset showed excellent linearity, with the regression equation S = 0.5000 C + 9.9906 (R² = 1.0000), where S is the fluorescence signal (a.u.) and C is the 2,4,5-T concentration (µg L⁻¹). Based on 16 independent blank measurements (σ = 0.12 a.u.), the limit of detection (LOD) and limit of quantification (LOQ) were 0.79 and 2.40 µg L⁻¹, respectively, and the quantitative working range was established as 2.40–1600 µg L⁻¹. The method showed satisfactory precision and accuracy, with recoveries close to 100
Rational design of functional organic dyes is vital in the development of optoelectronics and bioimaging fields, in which structural variety and synthesis feasibility should be considered. In this study, a holistic computational approach to investigate the chemical space of triphenylamine-derived chromophores is proposed by using similarity-based analysis, synthetic accessibility assessment, and fragmentation-based molecule generation methods. Through employing the BRICS algorithm, more than 10,000 new molecules were designed. The structural relationships among generated molecules were studied based on similarity score calculation, cluster formation, and visualization in the chemical space network. The selected standard molecules have shown good absorption properties and easy-to-use synthesis processes. Comparing the structural characteristics of three representative dyes (H1, H2, and H4), three different kinds of scaffolds can be recognized.
In this work, seven newly designed donor-acceptor1-spacer-acceptor2 (D-A1-π-A2) structured metal-free efficient organic compounds (A1-A7) were designed and tested for dye- sensitized solar cells (DSSCs). The D, π, and A groups were presented in (E)-2-(3-((E)-4-(dimethylamino)styryl)-5,5-dimethylcyclohex-2-enylidene)-2-cyanoacetic acid (D-1). The additional A components have been incorporated into the D-1 structure, and their influence on DSSC applications has been examined. Time-dependent density functional theory (TD- DFT) was used to determine the maximum absorption wavelength (λmax) of D-1 using hybrid functionals with a 6–311 + + G(2d,2p) basis set. According to these findings, TD-CAM-B3LYP used the same basis set and adhered to the optical λmax values for A1-A7. The solvent acetonitrile effects were followed in the literature with a conductor-like polarizable continuum model (C-PCM). The DFT and TD-DFT approaches were used to thoroughly study the molecular orbitals (MOs), λmax, and photovoltaic (PV) parameters of the molecules A1-A7. The computed results showed that all designed dyes offered better A-groups in D-A1-π-A2 sensitizers. The improved electronic transition, red-shifted λmax, and good PV characteristics of that structure make it a suitable chromophore for DSSCs.
Ratiometric fluorescence sensing is effective for environmental pollutant monitoring owing to self-calibration and anti-interference properties, but high-sensitivity and high-specificity probes for microcystin-LR (MC-LR) are still scarce. Herein, GP-AuNCs@Ce/Tb-BTC (Ce/Tb metal-organic framework based on benzene-1,3,5-tricarboxylic acid) was developed as a novel ratiometric fluorescent probe for aquatic MC-LR. Coordination interaction and suppressed non-radiative relaxation strengthen its fluorescence response, while dual-fluorescence ratiometric self-calibration optimizes detection stability. The optimized GP-AuNCs@Ce/Tb-BTC probe exhibits excellent sensing performance toward MC-LR, displaying a favorable linear response in the concentration range of 0.02–0.1 µg/mL with a low limit of detection (LOD) of 0.006 µg/mL, as well as outstanding selectivity and anti-interference capability. Practical water sample detection results verify the favorable accuracy and precision of this detection method, with spike recoveries ranging from 91.10
The compositional complexity and variability of crude oil demand rapid, reliable analytical methods for both refinery optimization and environmental forensics. Fluorescence spectroscopy is a sensitive, non-destructive alternative to conventional chromatographic and thermal techniques, yet its potential for quantitative, fraction-specific analysis remains under-exploited. In this work, SARA (saturates, aromatics, resins, asphaltenes) fractionation was integrated with systematic fluorescence profiling to characterize Iraqi Basra crude oil. Each fraction exhibited a distinct, reproducible fluorescence signature reflecting its underlying photophysics: the emission intensity of the saturate (alkane) and aromatic fractions increased linearly with concentration (0.001–0.04
Azo dyes are widely used in textile, food, cosmetic, and pharmaceutical industries due to their favorable drug-like properties. Their inherent fluorescence makes them promising candidates for bioimaging; however, low fluorescence intensity and quantum yield limit their practical applications. Recent studies suggest that nanoparticles, particularly carbon quantum dots (CQDs), can significantly enhance the fluorescence of dyes and fluorophores. In this study, we hypothesize that interaction between newly synthesized azo dyes and CQDs enhances fluorescence through specific photophysical mechanisms. The dye–CQD interactions were investigated using UV–Visible absorption, FTIR, steady-state, and time-resolved fluorescence spectroscopic techniques. Additionally, quantum yield, zeta potential and in vitro pharmacological evaluations (antibacterial, antioxidant, and hemolytic assays) were performed for azo dyes, CQDs, and their hybrid systems. Results revealed enhanced fluorescence intensity, prolonged excited-state lifetimes, and improved fluorescence quantum yields following interaction with CQDs. The enhancement was interpreted through Förster resonance energy transfer (FRET) and aggregation-induced emission (AIE) mechanisms. The azo dye–CQD hybrids exhibited synergistic antibacterial activity against E. coli and S. aureus, improved DPPH radical scavenging activity, and excellent hemocompatibility (< 2
Therapeutic drug monitoring of mycophenolic acid (MPA), the active metabolite of the immunosuppressant mycophenolate mofetil (MMF), is clinically important due to its narrow therapeutic window. In this work, a library-immobilized SELEX strategy was employed to isolate DNA aptamers capable of recognizing both MPA and MMF. Among the selected candidates, a dual-recognition aptamer (MPA-1) exhibited specific binding toward MPA and MMF, with dissociation constants (Kd) of 13.7 µM and 5.5 µM, respectively, as determined by a thioflavin T (ThT) fluorescence assay. Consistent binding affinities were obtained by microscale thermophoresis (MST), yielding Kd values of 3.1 µM for MPA and 0.78 µM for MMF. Notably, MPA-1 displayed negligible binding toward other immunosuppressive drugs and endogenous biomolecules, demonstrating excellent selectivity. Based on a strand-displacement strategy, a turn-on fluorescent aptasensor was subsequently constructed for the determination of MPA and MMF in 10
The recognition of Al3+ ion is significant due to their widespread presence in the environment and their potential toxic effects on human health. Therefore, the identification of these metal ions in various samples is of great importance. This review focuses on the key developments, design strategies, and progress of thiazole-based Schiff base chemosensors for the colorimetric and fluorometric detection of Al3+ ion. Thiazole Schiff bases displayed strong coordination affinity toward Al3+ through nitrogen, oxygen, and sulphur donor atoms, resulting in observable color variation and fluorescence enhancement. In this review, various thiazole-based Schiff bases are discussed to demonstrate their high selectivity, sensitivity, low detection limits (µM to pM), and rapid response times. The observed optical changes was demonstrated by different mechanisms, including chelation-enhanced fluorescence (CHEF), inhibition of photoinduced electron transfer (PET), intramolecular charge transfer (ICT), and excited-state proton transfer (ESPT), all of which play crucial roles in sensing behavior. Furthermore, several probes exhibit reversible binding and are applicable in environmental water and biological systems. Overall, thiazole-based Schiff base derivatives represent a promising class of colorimetric and fluorescent chemosensors for the detection of minute amounts of Al3+ ion, with wide applications in environmental monitoring, biomedical diagnostics, and intracellular imaging.
Hypochlorous acid (HOCl) serves as a vital molecule in innate immune defense, and fluctuations of lysosomal HOCl levels may be linked to a range of physiological and pathological processes, which make the quantitative detection of lysosomal HOCl a necessity. Herein, we report the design and synthesis of a novel fluorescent probe, PD-OCl, which is constructed by conjugating phenothiazine and dicyanoisophorone moieties and exhibits near-infrared (NIR) emission and large Stokes shifts. Notably, PD-OCl can function as a robust ratiometric fluorescent probe for HOCl detection, exhibiting exceptional selectivity, high sensitivity, and rapid response kinetics. Additionally, the PD-OCl has been successfully applied for monitoring both exogenous and endogenous HOCl in living cells, where it displays excellent lysosomal targeting capability, providing a visualized and ratiometric approach for tracing the variations of subcellular HOCl levels. This work establishes PD-OCl as a promising candidate for investigating lysosomal HOCl levels in LPS-induced oxidative stress state cells. A new probe, PD-OCl, with NIR emission and relatively large Stokes shifts was prepared. PD-OCl could detect HOCl with dual-channel ratiometric fluorescence analysis. The sensing was characterized with high selectivity and sensitivity, and a fast response. PD-OCl could image exogenous and endogenous lysosomal HOCl in living cells.
A narrow-band green-emitting phosphor KAl11O17(KAO): Eu2+, Mn2+, was synthesized via a high-temperature solid-state reaction to evaluate its potential for use in high-quality backlight displays. Structural refinement reveals that Eu2+ and Mn2+ ions preferentially occupy distinct crystallographic sites: Eu2+ resides at K+ sites in the conductive layer, whereas Mn2+ substitutes for tetrahedral Al3+ sites within the spinel block. This spatial separation facilitates efficient energy transfer (ET) from Eu2+ to Mn2+. Spectroscopic analysis of the optimally doped composition, KAO: 0.07Eu2+, 0.04Mn2+, indicates that the ET proceeds predominantly via a dipole - quadrupole (d-q) mechanism. The resulting phosphor exhibits bright green emission centered at 510 nm with an exceptionally narrow full width at half maximum (FWHM) of 8.13 nm, a high color purity of 98
A novel series of pyrrolo[1,2-f]azolo[1,5-a]pteridines has been synthesized via an efficient two-step annulation strategy. The photophysical properties of the resulting polyheteroaromatic fluorophores were systematically investigated in solution, solid state, and polymer films. In THF, the compounds exhibit intense emission in the visible region with high quantum yields (Ф up to 79.9
Impact of biotinylation strategy on the luminescent properties and quantum yield of carbon dots (CDs) is systematically investigated for four types of solvothermally synthesized CDs from citric acid and urea in dimethylformamide (CD-CU), citric acid in formamide (CD-CF), citric acid and ethylene diamine in formamide (CD-CEF), and glutathione in formamide (CD-GF) emitting in the 470–690 nm range. We compare direct carbodiimide coupling (EDC/NHS) with a two-step method employing presynthesized biotin NHS ester, followed by conjugation to CDs in aqueous media. Direct coupling (Method 1) leads to substantial quenching of surface-related emissive centers and formation of urea by-products, which strongly reduce photoluminescence quantum yield (PLQY), while careful purification partially restores the initial optical responses. In contrast, the NHS-ester strategy (Method 2) efficiently attaches biotin with minimal perturbation of the CD optical responses, preserving or even enhancing PLQY. In particular, glutathione/formamide-derived CDs (CD-GF) demonstrate the highest robustness: their deep-red emission is retained, and PLQY increases from 10.6
The development of fluorescent probes with large Stokes' shifts and high sensitivity remains a critical objective in chemical sensing and bioimaging. In this study, we report the design, synthesis, and comprehensive photophysical characterization of a novel regioisomeric bis(2-(2′-hydroxyphenyl)benzoxazole) scaffold, bis(HBO) 3, expanding the limited family of ESIPT-enabled bis(HBO) systems. This newly developed probe integrates two HBO units within a distinct C2′-symmetric framework, enabling systematic investigation of regio-effects on excited-state intramolecular proton transfer (ESIPT) behavior and analyte responsiveness. Photophysical studies reveal that bis(HBO) 3 exhibits characteristic ESIPT-driven emission with a large Stokes' shift (Δλ ≈ 160–180 nm) and solvent-independent fluorescence centered around λem ≈ 530 nm. In-depth spectroscopic analysis, including low-temperature fluorescence measurements, demonstrates the presence of multiple emissive keto rotamers, providing insight into the role of conformational dynamics in modulating emission behavior. Compared with previously reported bis(HBO) analogues 1 and 2, bis(HBO) 3 displays distinct emission features due to a pronounced regio-effect. Bis(HBO) 3 exhibited selective responsiveness toward several chemical analytes. The probe shows high stability under acidic conditions but undergoes deprotonation in the presence of strong bases and certain metal ions, particularly Cu(II), Ni(II) and Fe(II), resulting in pronounced spectral changes. Notably, bis(HBO) 3 exhibits a distinct and sensitive response toward fluoride anions, characterized by the emergence of a new absorption band ( 415 nm) and a blue-shifted emission ( 485 nm). Quantitative analysis using the Benesi–Hildebrand method confirms a 1:1 binding stoichiometry with moderate binding affinity, distinguishing its sensing behavior from previously reported bis(HBO) systems that exhibit 1:2 binding stoichiometry. Overall, this work summarizes bis(HBO) 3 as a unique ESIPT-based fluorescent skeleton and highlights the critical role of molecular symmetry and regio-effects in governing photophysical and sensing properties.
The fluorescence response of a Schiff base ligand (L), synthesized from 4-(aminomethyl)indole and 2,3-dihydroxybenzaldehyde, was investigated in the presence of cyanide ions in a CH3CN/H2O (7:3, v/v) medium. Mechanistic investigations indicate that cyanide recognition proceeds through nucleophilic addition at the imine center rather than conventional non-covalent interaction, altering the electronic structure of the molecule and generating a strongly emissive species. This transformation was confirmed by 1H NMR titration and further supported by ESI–MS analysis. Density functional theory (DFT) calculations further revealed a marked redistribution of frontier molecular orbitals together with an increase in the HOMO–LUMO energy gap from 4.24 to 5.01 eV, consistent with the experimentally observed fluorescence activation. As a consequence of this reaction-driven process, ligand L displayed a pronounced emission enhancement at 474 nm upon exposure to CN⁻, whereas other tested anions produced negligible responses. Quantitative fluorescence measurements yielded an association constant of 5.66 × 104 M⁻1 and a detection limit of 0.055 µM. A 1:1 probe–cyanide stoichiometry was established from continuous variation studies and further supported by ESI–MS analysis. These findings demonstrate that reaction-induced structural transformation of the Schiff base framework enables selective fluorescence-based cyanide sensing.
The photophysical properties of a heterobimetallic IrIII–EuIII complex were investigated in solvents with different polarity, coordinating ability, and vibrational characteristics to elucidate the factors governing EuIII sensitization. Steady-state and time-resolved luminescence measurements revealed that the solvent profoundly influences both the donor-to-acceptor energy-transfer process and the europium-centered emission. The apparent IrIII → EuIII energy-transfer rate constants (kET) and donor-to-acceptor energy-transfer efficiencies (ηET) were estimated from the residual 3MLCT emission lifetimes (τq) of the IrIII–EuIII complex and the corresponding IrIII–GdIII analog (τu). The results showed a general tendency toward higher energy-transfer rates and efficiencies in solvents with high polarity, coordinating ability, and free of O–H oscillators, reaching kET values up to 2.6 × 107 s−1 and ηET values up to 90
A violet laser of wavelength 405 nm is used to excite steady-state fluorescence in the juice of a lemon. Prominent wavelength peaks appear at 520 and 670 nm due to emissions from riboflavin (vitamin B2) and protochlorophyllide (pchlide), the precursor of chlorophyll a , respectively. Using a polariser for excitation with vertically polarised light, and another one in parallel as well as in perpendicular positions to this one in the emission-path, counts at the two peaks in the high-resolution spectrometer are noted. Fluorescence anisotropies calculated from the obtained intensities at the two positions of the analyser reveal that the value at 520 nm peak is approximately twice that of the 670 nm one. This indicates that rotational mobility of riboflavin is much less than protochlorophyllide, even though the latter is much larger and more complex, in the low pH (high acidity) medium.
Lead ions (Pb2+), as heavy metal ions, pose significant hazards to human health. Therefore, it is of great significance to establish a simple and effective method for detecting Pb2+. In this study, a label-free Pb2+ biosensor was established based on G-quadruplex DNA (G4-DNA) and Exonuclease III (Exo III). In the absence of Pb2+, the double-stranded DNA formed by G4-DNA and its complementary strand can be cleaved by Exo III. When Pb2+ was present, G4-DNA can form a cage-like structure with the assistance of Pb2+, thereby disrupting the formation of double-stranded structures and blocking the cleavage of DNA by Exo III. Subsequently, the fluorescence signal was released upon the addition of the DNA dye (SG I). This biosensor possessed a broad linear detection range of 10 nM – 20 µM and a low limit of detection (LOD) of 7.3 nM. Moreover, the proposed biosensor exhibited excellent specificity for Pb2+ and achieved satisfactory recovery rates (91.4
Doping represents a critical threat to the integrity of competitive sports, with diuretics frequently misused as masking agents to facilitate the urinary excretion of other prohibited substances. Torsemide (TSD), a widely misused loop diuretic, requires a sensitive and selective method for its determination in biological matrices to support efficient doping control. Herein, a sustainable fluorescent nanosensor based on multi-self-doped carbon quantum dots was synthesized for the first time from golden berry (GBQDs) via a rapid, one-step microwave-assisted approach at 800 W in just 7 min without additional surface passivation agents. Notably, these innovative CDs outperform previous traditional methods, as their preparation relies on minimum energy consumption and green natural substrate. The fabricated GBQDs exhibited intense blue fluorescence at λex/λem 350/423 nm, a quantum yield of 28.9
In this work, bisNAPTPA and its derivative bisNAPTPA-OCH3 have been investigated to reveal how targeted methoxy substitution tunes the photophysical properties in symmetric naphthalimide derivatives. Combined experimental and theoretical analyses reveal that the introduced methoxy groups at the terminals of triphenylamine groups not only induce distinct aggregation-induced emission (AIE) by restricting intramolecular motions, as confirmed by time-resolved fluorescence, but also significantly enhance intramolecular charge transfer (CT). This enhanced intramolecular CT characteristic leads to a red shift in absorption and a notable improvement in the two-photon absorption (TPA) cross-section. Visualization of excited states via transition density matrix and charge density difference analyses provides a mechanistic understanding of the superior electron delocalization and nonlinear optical response in bisNAPTPA-OCH3. Our findings suggest that methoxy functionalization represents a promising molecular design motif for simultaneously enhancing AIE characteristics and TPA performance in symmetric naphthalimide derivatives.
Excited-state intramolecular proton transfer (ESIPT)-based fluorescent probes have emerged as powerful tools for bioimaging and chemical sensing owing to their large Stokes shifts, dual-emission characteristics, high sensitivity, and reduced self-absorption effects. These unique photophysical properties have facilitated the development of advanced fluorescent probes for the detection of biologically important gasotransmitters, including carbon monoxide (CO), nitric oxide (NO), and hydrogen sulfide (H2S), which play crucial roles in numerous physiological and pathological processes. This review provides a comprehensive overview of ESIPT-based fluorescent probes reported for the detection of these gasotransmitters, with emphasis on their molecular design strategies, sensing mechanisms, photophysical properties, and biological applications. The reported systems are systematically classified according to their recognition units and analyte-triggered transformations, highlighting the mechanisms responsible for ESIPT modulation and fluorescence signal generation. Particular attention is given to representative fluorophore platforms, including benzothiazole, quinoline, flavone, and related derivatives, as well as the integration of ESIPT with intramolecular charge transfer (ICT), aggregation-induced emission (AIE), and near-infrared (NIR) fluorescence for enhanced analytical performance. Comparative analysis of the reported probes reveals the advantages and limitations of different sensing strategies with respect to sensitivity, selectivity, response kinetics, and biological applicability. Current challenges, including probe toxicity, interference from competing species, and limited in vivo applicability, are critically discussed. Finally, future perspectives toward metal-free systems, multimodal sensing platforms, NIR-emissive probes, and clinically relevant bioimaging applications are presented. This review aims to provide a systematic understanding of ESIPT-based gasotransmitter probes and to offer insights for the rational design of next-generation fluorescent sensing platforms.
