[en] The spectroscopic and laser characteristics of two benzopyrane derivatives for 600–670 nm spectrum region of lasing in preliminarily annealed silica xerogel matrices in non-selective cavity under laser pumping at 551 nm have been measured and analysed. The influence of molecular structure of the dyes on their non-radiating losses has been revealed. The specific output laser energy of the studied matrices was approximately equal to the ones for corresponding methanol solutions under the same pumping conditions. The laser spectra of the matrices were displaced to the red region from the fluorescence maximum by about 1000–1500 cm⁻¹ in a nonselective cavity. Such spectral displacement may improve the characteristics of biosensors made on the basis of these matrices because it shifts their emission spectrum to the range of deeper penetration into biological tissues.

[en] Novel luminophors of anthracene (AN) and tetracene (TN) doped biphenyl were prepared using Conventional Solid State reaction technique. Fluorescence spectroscopy, XRD, SEM, TGA-DSC and Cyclic Voltammetry techniques have been employed for photophysical, electrochemical and thermal study. The X-ray diffraction study revealed the formation of homogeneous biphenyl solid solutions with the added guests AN and TN. Fluorescent biphenyl absorbing short wave UV radiation and emitting at long wave UV radiation has been used as a solid matrix. From the fluorescence spectra it is seen that the added guests shifts the UV fluorescence of biphenyl emitting in green region of visible spectrum at 532 nm. SEM images of the prepared luminophors showed the crystallites of average size 140 nm which makes them suitable candidates for their use in Optoelectronic devices. HOMO and LUMO energy levels of the synthesized luminophors from electrochemical data observed in 5.50–5.64 eV and 3.09–3.13 eV with band gap 2.37–2.55 eV, respectively. TGA-DSC study revealed the thermal stability of prepared luminophors.

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[en] A novel copolymer poly(thiophene-2,5-diyl-2,5-di-n-octyloxycarbonyl-1,4-phenylene), denoted as P33, is introduced as potential material for photovoltaics, polymer light-emitting diodes, and/or organic transistors. P33 dissolved in chloroform is investigated by steady-state absorption, linear/non-linear fluorescence spectroscopies and time-resolved fluorescence spectroscopy. Molar extinction coefficient, fluorescence quantum yield, and singlet fluorescence lifetime of P33 are determined to be 18,315 M⁻¹ cm⁻¹, 0.4, and 810 ps, respectively. The P33 fluorescence fast components of decay times are 1.2 ps, 2.0 ps, and 0.5 ps for increasing wavelengths of 480 nm, 500 nm, and 520 nm, respectively. The fast component is attributed to a transport of nearly instantaneously formed excitons to localized states known as downhill energy transfer. Additionally multi-photon excited fluorescence is observed for pumping with wavelengths of 800 nm and 1200 nm. Two-photon absorption cross-section is determined to be 6.9 GM. These spectroscopic studies provide basic fluorescence characteristics of the novel thiophene copolymer P33.

[en] We show that unsymmetric BODIPY compounds with one, two, and three methyl groups can be synthesized easily and efficiently by the unsymmetric reaction method. Their steady state and time-resolved fluorescence properties are examined in solvents of different polarity. These compounds show high fluorescence quantum yields (0.87 to 1.0), long fluorescence lifetimes (5.89 to 7.40 ns), and small Stokes shift (199 to 443 cm⁻¹). The methyl substitution exhibits influence on the UV-Vis absorption and fluorescence properties, such as the blue shift in emission and absorption spectra. It is the number rather than the position of methyls that play major roles. Except for 3 M-BDP, the increase in the number of methyls on BODIPY core leads to the increase in both fluorescence quantum yield and radiative rate constant, but causes the decrease in fluorescence lifetime. H-bonding solvents increase both the fluorescence lifetime and quantum yields. The methylated BODIPYs show the ability to generate singlet oxygen (¹Δ_g) which is evidenced by near-IR luminescence and DPBF chemical trapping techniques. The formation quantum yield of singlet oxygen (¹Δ_g) for the compounds is up to 0.15 ± 0.05.

[en] We have synthesized and characterized of a series of single and multidye copolymerized nanoparticles with large to very large Stokes shifts (100 to 255 nm) for versatile applications as standalone or multiplexed probes in biological matrices. Nanoparticles were prepared via the Stöber method and covalently copolymerized with various combinations of three dyes, including one novel aminocyanine dye. Covalently encapsulated dyes exhibited no significant leakage from the nanoparticle matrix after more than 200 days of storage in ethanol. Across multiple batches of nanoparticles with varying dye content, the average yields and average radii were found to be highly reproducible. Furthermore, the batch to batch variability in the relative amounts of dye incorporated was small (relative standard deviations ≤2.3%). Quantum yields of dye copolymerized nanoparticles were increased 50% to 1000% relative to those of their respective dye-silane conjugates, and fluorescence intensities were enhanced by approximately three orders of magnitude. Prepared nanoparticles were surface modified with polyethylene glycol and biotin and bound to streptavidin microspheres as a proof of concept. Under single wavelength excitation, microsphere-bound nanoparticles displayed readily distinguishable fluorescence signals at three different emission wavelengths, indicating their potential applications to multicolor sensing. Furthermore, nanoparticles modified with polyethylene glycol and biotin demonstrated hematoprotective qualities and reduced nonspecific binding of serum proteins, indicating their potential suitability to in vivo imaging applications.

[en] We designed and synthesized a simple fluorescent probe, (E)-2-(2-(3,4,5-Trimethoxybenzylidene)hydrazinyl) benzothiazole (probe), which could be applied to the detection of strongly acidic and alkaline pH in DMSO/water (1/4, v/v) system. It could be used to quantitatively detect strong acid in the range of 2.60–3.53 with a pK_a of 2.78. Meanwhile, it also showed an excellent linear relationship between the fluorescence intensity and alkaline pH values over the range of 9.98–10.95 with a pK_a of 9.32. The probe exhibited excellent properties to pH with high selectivity and sensitivity. The mechanism studies showed that the H⁺ binding with the N atom of benzothiazole moiety and hydrazine moiety in acid solution while the deprotonation of N atom in hydrazine group in basic environment. Importantly, the probe was successfully applied for imaging the strongly acidic and alkaline in E.coil cells.

[en] A fluoro-based Schiff base (E)-2-fluoro-N′-(1-(4-nitrophenyl)ethylidene)benzohydrazide (FNEB) has been synthesized from condensation of 2-fluorobenzohydrazide and 4′-nitroacetophenone catalyzed by glacial acetic acid with ethanol as the solvent. The dipole moment of FNEB in both the electronic states were found using different solvatochromic approaches such as Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet, Reichardt and Bilot-Kawski. The experimental ground state dipole moment of FNEB was calculated using Guggenheim-Debye method and theoretical ground state dipole moment using Bilot-Kawski solvatochromic approach. The solvatochromic behavior of the Schiff base in different solvents was studied using absorption and emission spectra. Catalan and Kamlet-Abboud-Taft parameters were used from the multiple linear regression (MLR) analysis in order to study the solute-solvent interaction. The dipole moments were also calculated using Time Dependent-Density Functional Theory (TD-DFT). The chemical stability of FNEB was determined using computational and Cyclic Voltammetry by the use of obtained energy gap between the frontier orbitals. Using the frontier orbitals energy gap, global reactivity parameters were computed. Further, Light Harvesting efficiency was determined to comprehend the photovoltaic property of the Schiff base.

[en] Nitrogen doped carbon quantum dots (NCQDs) were synthesized via hydrothermal route. The NCQDs are thermally and optically stable with high flouresence yield. For the synthesis of NCQDs, citric acid and urea was taken as carbon and nitrogen sources, respectively. The Transmission Electron Microscopy (TEM) of these quantum dots revealed nearly spherical shape and average size of 1.5 nm, which was calculated using Image J software. The quantum dots were also well-characterized using spectroscopic techniques such as FTIR, UV-Visible absorption and fluorescence. These synthesized and characterized dots were utilized for selective detection of lactose in Milli Q water. The bioprobe provide a wide linear range varying from (10.00–77.41) μM with limit of detection 11.36 μM and sensitivity equal to (0.0065 ± 0.0002) μM⁻¹.

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[en] A novel fluorescent sensor (L) based on 1,8-naphthalic anhydride has been developed which can selectively detect Cu²⁺ in CH₃CN medium over other metal ions at 408 nm in the fluorescence spectra. When Cu²⁺ was added into L, L showed fluorescent turn-off by coordinating with Cu²⁺. A fresh absorption band was found at the position of 290 nm as was a red-shifted absorption band from 356 nm to 376 nm in UV-vis spectra which might be attributed to the intramolecular charge transfer (ICT). Meanwhile, L-Cu²⁺ showed fluorescence quenching via photoinduced electron transfer (PET). The complexation ratio was proposed to be 1:1 which was determined by Job’s plot, fluorescence titration and ¹H NMR titration. The detection limit was 9.1 × 10⁻⁸ mol·L⁻¹, a satisfying level to detect Cu²⁺ in the micromolar scale. Corresponding molecular geometries, orbital energies and electron contributions of sensor L were calculated by the DMol3 program package using the density functional theory.

[en] We fabricated a new and selective fluorescent sensor for the detection of citrate by employing g-C₃N₄ quantum dots (g-CNQDs) and MgFe layered double hydroxide (MgFe-LDH). The g-CNQDs interacted with MgFe-LDH via electrostatic interaction and the fluorescence of g-CNQDs was effectively quenched by MgFe-LDH due to inner filter effect. Upon addition of citrate, the fluorescence of the g-CNQDs was significantly enhanced, arising from the replacement of g-CNQDs by citrate because citrate competed with g-CNQDs to form more stable complexes with MgFe-LDH. Therefore, we developed a “turn-off–on” fluorescence assay method for the detection of citrate. This method enabled the selective detection of citrate with linear range of 0.5–3.0 μM and 3.0–10.0 μM with a 12.3 nM limit of detection. This method exhibited advantages including easy preparation, environmentally friendly process and rapid response toward citrate.