Search Results (188)

BOPAM exhibits high fluorescence quantum yields, along with exceptional photostability, rendering it a promising platform for applications as fluorescence sensors. However, the development of BOPAM-based fluorophores with extended emission wavelengths remains limited, and the underlying mechanisms of fluorescence quenching via the population of dark twisted intramolecular charge transfer (¹TICT) excited states are not yet fully understood. To address these gaps, we synthesized a series of BOPAM derivatives by incorporating electron-donating groups at the boron atoms and the phenyl rings of the BOPAM core. The introduction of bromide, phenyl, and naphthyl groups preserved the intrinsic locally excited (¹LE) emission of BOPAM. In contrast, the incorporation of diphenylamine (BP-DA) and triphenylamine (BP-TA) moieties resulted in a red-shifted emission, attributed to an enhanced intramolecular charge transfer (ICT) process. Notably, in acetonitrile, BP-DA exhibited weak fluorescence originating from a ¹TICT state, which was populated via the S₂ → ¹TICT transition. Furthermore, the emission observed from BP-TA was associated with a higher-lying excited state, likely the initially populated S₂ state possessing a ¹LE character. These findings not only introduce novel red-emissive BOPAM-based fluorophores, but also offer valuable insights into the role of the S₂ state in governing fluorescence quenching mechanisms in BOPAM derivatives. Full article

Photochemical degradation is a major removal pathway for pharmaceutical pollutants in water, and dissolved organic matter (DOM) in water is an important factor affecting this process. This study investigates the differential effects of seasonally-varied dissolved organic matter (DOM) from Songhua River and Liao River on the photodegradation of pharmaceutical pollutants, using levofloxacin (LFX), sulfamethoxazole (SMZ), and ibuprofen (IBP) as target compounds. The results demonstrated that summer and autumn DOM inhibited the photodegradation of LFX and SMZ through light screening and dynamic quenching effects, with inhibition rates of 35.1% and 55.5%, respectively, whereas winter DOM enhanced degradation through photo-oxidation mechanisms. DOM from Songhua River and Liao River significantly promoted the photodegradation of IBP. Quenching experiments showed differences in the contributions of photochemically reactive intermediates (PPRIs) to the photodegradation of different target pollutants, with hydroxyl radicals (•OH) dominating LFX photodegradation (48.79% contribution), excited triplet states of DOM (³DOM*) dominating SMZ photodegradation (85.20% contribution), and singlet oxygen (¹O₂) dominating IBP photodegradation (79.89% contribution). The photodegradation pathways were elucidated by measuring the photodegradation by-products of the target pollutants: LFX mainly underwent piperazine ring cleavage and oxidative decarboxylation, SMZ underwent isoxazole ring opening and deamination during photodegradation, and IBP underwent photodecarboxylation and oxidation reactions. Under the influence of the DOM from the Songhua River and Liao River, the generation of multiple photodegradation by-products led to an increasing trend in the acute toxicity of target pollutants to luminescent bacteria. This investigation elucidates the dual regulatory mechanisms of natural aquatic DOM on both photo-induced degradation pathways and toxicity evolution dynamics of pharmaceutical contaminants, which is of great significance for understanding the photochemical transformation behavior and risk assessment of pharmaceutical pollutants in aquatic environments. Full article

Non-hygroscopic borosilicate glasses containing Ce³⁺ and Mn²⁺ ions were prepared using the conventional melt-quenching method. The electrochemical equilibrium of the Ce and Mn oxidation states has a significant effect on the energy levels and luminescence of both elements. Consequently, the oxidation states in the glasses were analyzed using a combination of XPS, EPR, and absorption spectroscopy. The oxidation–reduction equilibrium was altered by systematically changing three factors: the Mn concentration, the presence or absence of SnO as a reducing agent, and the optical basicity of the glass. Upon excitation with light with a wavelength of 320 nm, the prepared glasses exhibited a blue luminescence band in the region of 350–450 nm, corresponding to the Ce³⁺ ion, and a broad, weak red luminescence emission in the region of 540–640 nm, corresponding to Mn²⁺ ions. To obtain a high luminescence intensity for both bands, it was necessary to reduce the MnO content below 1 mol.%. Furthermore, doping the glasses with Sn²⁺ ions helped to maintain both cerium and manganese in low oxidation states, resulting in measurable luminescence in both observed bands. These low oxidation states of Ce and Mn can also be achieved by reducing the optical basicity of the glass through the addition of MgO. The general relationships obtained could potentially be applied in the production of light-emitting diodes or field-emission displays that utilize energy transfer. Full article

A set of three-dimensional metal-organic frameworks, named MOF-76, belonging to the tetragonal P4₃22 space group, based on [Y(BTC)(H₂O)](DMF)_1.1 (1,3,5-benzenetricarboxylate) doped with Eu³⁺, Tb³⁺, and Eu³⁺/Tb³⁺ were obtained under solvothermal conditions and fully characterized by powder X-ray diffraction, thermal, and vibrational analyses. In addition, upon UV light excitation (280 nm), all the powdered samples exhibited fine 4f-4f transitions, of which the ⁵D₀ → ⁷F₂ (Eu³⁺) and ⁵D₄ → ⁷F₅ (Tb³⁺) were the most intense ones. All samples were photophysically analyzed by determining the luminescence lifetimes, and their emission colors were quantified by calculating their chromaticities and color purities. Moreover, the intrinsic quantum yield, radiative, and non-radiative constants were calculated and compared to establish a structure–property relationship. Specifically, the Eu/Tb co-doped sample was employed to monitor its hypersensitive emissions in the presence of small volatile organic compounds (VOCs), showing quenching or enhancement of emission in protic and non-protic solvents. Furthermore, DFT calculations were carried out to understand the energy transfer processes between the sensor and the respective analytes. These results are promising for the development of solid-state lighting devices and colorimetric chemical sensors for specific compounds. Full article

Stimulus-responsive inorganic–organic hybrid metal halides (IOMHs) have shown great potential in applications such as sensing and anti-counterfeiting. IOMHs can undergo a variety of structural changes when triggered by humidity; however, relevant reports of structural dimensionality change from zero dimension (0D) to one dimension (1D) are rare. This study investigates the synthesis, structure, and properties of two antimony-based IOMHs, namely 0D-(Mp)₃SbCl₆·MeCN and 1D-(Mp)₂SbCl₅ (Mp = protonated morpholine; MeCN = acetonitrile). Photophysical characterizations show that (Mp)₃SbCl₆·MeCN, when being excited at 375 nm, exhibits typical self-trapped exciton triplet state broad-band emission, with a peak at 620 nm and a quantum yield as high as 75.06%. Under humid conditions, the 0D structure of (Mp)₃SbCl₆·MeCN undergoes a phase transition, leading to the 1D structure of (Mp)₂SbCl₅. This transition is accompanied by fluorescence quenching. X-ray powder diffraction, Raman spectroscopy, and thermogravimetric analysis confirm the phase transition process and its reversibility. Based on the high contrast of fluorescence before and after phase transition, (Mp)₃SbCl₆·MeCN is demonstrated as an ideal material for fluorescence water sensing, capable of detecting trace amounts of water in tetrahydrofuran with a detection limit of 0.2% v/v. Full article

Triplet–triplet transfer photochemical reactions are essential in many biological, chemical, and photonic applications. Here, the Pd-octaethylporphyrin sensitizer along with triplet–triplet annihilator (TTA) active 9,10-diphenylantracenes (DPA) and the related substituted variants in low concentrations were examined. A full experimental approach is presented for finding the necessary rate parameters with statistical standard deviation parameters. This was achieved by solving the pertinent non-analytical kinetic differential equation and fitting it to the experimental time-resolved photoluminescence of both slow fluorescence and sensitizer phosphorescence. The efficiency of the triplet–triplet energy transfer rate was found to be around 90% in THF but only around 75% in toluene. This appears to follow from the shorter lifetime of the sensitizer triplet in toluene. Moreover, the TTA transfer rate was on average more than 40% in THF toluene whereas a considerably lower value around 20–30% was found for toluene. This originated in an order of magnitude higher solvent quenching rate using toluene, based on the analysis of the delayed fluorescence decay traces. These are also higher than the statistically expected 1/9 TTA efficiency but in accordance with recent results in the literature, that attributed these high values to an inverse intersystem crossing process. In addition, quantum chemical calculations were carried out to reveal the pertinent excited triplet molecular orbitals of the lowest triplet excited state for a series of substituted DPAs, in comparison with the singlet ground state. Conclusively, these states distribute mainly in an anthracene ring in all compounds being in the range 1.64–1.65 eV above the ground state. The TTA efficiency was found to vary depending on the DPA annihilator substitution scheme and found to be smaller in THF. This is likely because the molecular framework over which the T1 excited molecular orbitals distribute is less sensitive for a longer lifetime of the annihilator triplet state. Full article

β-galactosidase (β-Gal) has emerged as a pivotal biomarker for the comprehensive investigation of diseases associated with cellular senescence. The development of a fluorescent sensor is of considerable importance for precisely detecting the activity and spatial distribution of β-Gal. In this study, we developed two excited-state-altering responsive fluorescent sensors (TF1 and TF2) for ratiometric detection of β-Gal. Two TCF dyes, composed of tricyanofuran (TCF) and naphthol units, feature electron “pull–push” systems and are quenched fluorescence by β-Gal. Upon β-Gal hydrolysis, a significant ratiometric shift in absorption from ca. 475 nm to 630 nm is observed, accompanied by the emergence of a fluorescence signal at ca. 660 nm. The enzyme-responsive optical red-shifts are attributed to the excited-state transition from intramolecular charge transfer (ICT) state to local excited (LE) state, which was confirmed by density functional theory (DFT) calculations. Both fluorescent sensors display exceptional sensitivity and selectivity for the response of β-Gal in PBS solution and are capable of tracking β-Gal within senescent A549 cells. This study introduces a framework for developing multimodal optical probes by systematically modulating excited-state properties, demonstrating their utility in senescence studies, diagnostic assay design, and therapeutic assessment. Full article

Singlet oxygen quantum yield (Φ_Δ) is a critical parameter in photodynamic studies, particularly for evaluating photosensitizers’ efficiency in diverse applications such as photodynamic therapy and environmental remediation. Standard photosensitizers, including Rose Bengal, Methylene Blue, and porphyrins, are widely employed as benchmarks for determining Φ_Δ. However, accurate determination of Φ_Δ relies not only on the intrinsic properties of these photosensitizers but also on their experimental conditions, such as concentration. This study investigated the influence of photosensitizer concentration on singlet oxygen quantum yield using several standard photosensitizers. Our findings revealed a significant decrease in Φ_Δ with increasing photosensitizer concentrations across all tested compounds. This decline was attributed to self-quenching effects and molecular aggregation, which reduced the efficiency of energy transfer from the excited triplet state of the photosensitizer to molecular oxygen. The results emphasize the importance of optimizing photosensitizer concentration to ensure reliable Φ_Δ measurements and avoid underestimations. This work underscores the need to consider concentration-dependent effects in future studies to ensure accurate and reproducible outcomes. Full article

Interactions between excitatory and inhibitory neurons in the cerebral cortex give rise to different regimes of activity and modulate brain oscillations. A prominent regime in the cortex is the inhibition-stabilized network (ISN), defined by strong recurrent excitation balanced by inhibition. While theoretical models have captured the response of brain circuits in the ISN state, their connectivity is typically hard-wired, leaving unanswered how a network may self-organize to an ISN state and dynamically switch between ISN and non-ISN states to modulate oscillations. Here, we introduce a mean-rate model of coupled Wilson-Cowan equations, link ISN and non-ISN states to Kolmogorov-Sinai entropy, and demonstrate how homeostatic plasticity (HP) allows the network to express both states depending on its level of tonic activity. This mechanism enables the model to capture a broad range of experimental effects, including (i) a paradoxical decrease in inhibitory activity, (ii) a phase offset between excitation and inhibition, and (iii) damped gamma oscillations. Further, the model accounts for experimental work on asynchronous quenching, where an external input suppresses intrinsic oscillations. Together, findings show that oscillatory activity is modulated by the dynamical regime of the network under the control of HP, thus advancing a framework that bridges neural dynamics, entropy, oscillations, and synaptic plasticity. Full article

The self-activated halotungstate Ba₃WO₅Cl₂ was successfully synthesized using a high-temperature solid-state method. X-ray diffraction analysis (XRD) confirmed the formation of a single-phase compound with a monoclinic crystal structure, ensuring the material’s purity and structural integrity. The luminescence properties of Ba₃WO₅Cl₂ were thoroughly investigated using both optical and laser-excitation spectroscopy. The photoluminescent excitation (PLE) and emission (PL) spectra, together with the corresponding decay curves, were recorded across a broad temperature range, from 10 K to 480 K. The charge transfer band (CTB) of the [WO₅Cl] octahedron was clearly identified in both the PL and the PLE spectra under ultraviolet light excitation, indicating efficient energy transfer within the material’s structure. A strong blue emission could be detected around 450 nm, which is characteristic of the material’s luminescent properties. However, this emission exhibited thermal quenching as the temperature increased, a common phenomenon where the luminescence intensity diminishes due to thermal effects. To better understand the thermal quenching behavior, variations in luminescence intensity and decay time were analyzed using a straightforward thermal quenching model. This comprehensive study of Ba₃WO₅Cl₂ luminescent properties not only deepens the understanding of its photophysical behavior but also contributes to the development of novel materials with tailored optical properties for specific technological applications. Full article

Carbon dots (CDs) derived from biomass are promising fluorescent probes for specific analyte detection due to their specificity, biocompatibility, selectivity, and sensitivity. In this work, carbon dots were prepared hydrothermally from natural material, Myrica esculenta fruits (hereafter referred to as MPCDs), without adding any chemicals. The prepared MPCDs were characterized using optical, microscopic, and spectroscopic methods that revealed the presence of numerous functional groups and fluorescent properties. MPCDs exhibited exceptional characteristics such as water solubility, photostability, excitation-dependent fluorescence emission, and ionic stability. Transmission electron microscopy found that the average size of the MPCDs was 8 nm. MPCDs exhibited remarkable sensing ability for hemin, with a good linearity (R² = 0.999) and a lower limit of detection of 14.1 nM. MPCDs demonstrated fluorescence quenching-based detection of hemin, primarily owing to ground state complex formation and the inner filter effect. Furthermore, the prepared material exhibited excellent antioxidant potential against 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) and 2,2-diphenyl-1-picrylhydrazyl radicals with EC₅₀ values of 25.4 and 205.4 µg/mL, respectively. The study suggests that CDs from Myrica esculenta fruits could be used as optical sensors for hemin detection as well as to scavenge selected radicals. Full article

In this study, ion-beam-induced luminescence with 2 MeV H⁺ was used to excite YAG single crystals at different temperatures. Under several constant temperatures, the luminescence intensity of Yb²⁺ monotonically decreases with increasing fluence, eventually reaching approximately 35% of the initial intensity at a fluence of 3.5 × 10¹⁴ cm⁻². The nonmonotonic evolution behavior of Yb²⁺ luminescence intensity with temperature can be effectively described by the intermediate-state model under consecutive temperature variations. The presence of an intermediate state may be the primary cause of the negative thermal quenching of Yb²⁺ luminescence. Yb²⁺ luminescence intensity decreased to 60% of the initial intensity when the temperature was continuously varied in the 100–300 K range, although the peak position remained rather stable. The luminescence of Yb²⁺ exhibits good radiation resistance and thermal stability in the experimental temperature range. Full article

This study employs quantum chemical computational methods to predict the spectroscopic properties of fluorescent probes 2,6-bis(2-benzimidazolyl)pyridine (BBP) and (E)-3-(2-(1H-benzo[d]imidazol-2-yl)vinyl)-9-(2-(2-methoxyethoxy)ethyl)-9H-carbazole (BIMC). Using time-dependent density functional theory (TDDFT), we successfully predicted the fluorescence emission wavelengths of BBP under various protonation states, achieving an average deviation of 6.0% from experimental excitation energies. Molecular dynamics simulations elucidated the microscopic mechanism underlying BBP’s fluorescence quenching under acidic conditions. The spectroscopic predictions for BIMC were performed using the STEOM-DLPNO-CCSD method, yielding an average deviation of merely 0.57% from experimental values. Based on Einstein’s spontaneous emission formula and empirical internal conversion rate formulas, we calculated fluorescence quantum yields for spectral intensity calibration, enabling the accurate prediction of experimental spectra. To streamline the computational workflow, we developed and open-sourced the EasySpecCalc software v0.0.1 on GitHub, aiming to facilitate the design and development of fluorescent probes. Full article

In this study we report on the efficiency of a furane-indole-chromenone-based organic derivative (FIC) as a photocatalyst in the α-arylation of enol acetate upon LED irradiation at 405 nm, and as a photoinitiator/photocatalyst in the free radical polymerization of an acrylate group in the presence of bis-(4-tert-butylphenyl)iodonium hexafluorophosphate (Iod) as an additive, or in the presence of both Iod and ethyl-4-(dimethyl amino) benzoate (EDB) under LED irradiation at 365 nm. The photochemical properties of this new light-sensitive compound are described, and the wide redox window (3.27 eV) and the high excited-state potentials FIC*/FIC^●− (+2.64 V vs. SCE) and FIC^●+/FIC* (−2.41 V vs. SCE) offered by this photocatalyst are revealed. The chemical mechanisms that govern the radical chemistry are discussed by means of different techniques, including fluorescence-quenching experiments, UV-visible absorption and fluorescence spectroscopy, and cyclic voltammetry analysis. Full article

Stimulus-responsive luminescent materials are pivotal in the field of sensing. Fluorescent transition metal complexes with a charge transfer excited state, especially terpyridine-coordinated polymers, are of particular interest due to their tunable emission. In this paper, a novel bis-terpyridine ligand was synthesized and assembled into a coordination polymer, which showed intense visible light absorption and fluorescence emission in the solid state that could be regulated by an acidic or basic pH. After being protonated by acid, the fluorescence of the polymer P2 was quenched. The emission of the polymer split from 635 nm to two peaks of 674 and 440 nm, and then stabilized at 728 nm for 7 days, which showed a significant red-shift and good protonation stability. The fluorescence emission wavelength of the protonated polymers recovered after alkalization, and the fluorescence intensity of the polymer was greatly improved after alkalization, showing interesting acid–base-response luminescence characteristics. The sensitive response of the synthesized coordination polymers to acids and bases will contribute to expanding the application of linear coordination polymers in sensing and other fields. Full article