Temperature Dependence Of Fluorescence Spectra Research Articles

Impact of the spatial structure of alkyl chains on properties of thiophene-substituted diketopyrrolopyrroles: Part II – Spectroscopic study

The study concerns the impact of a difference in geometry of the side alkyl chains of oligothiophene derivatives of diketopyrrolopyrrole (DPP) on their spectroscopic properties and aggregation in solutions, in Langmuir layers, and thin films. Using a combination of theoretical and experimental approaches, this study aims to explain the aggregating behaviour of thiophene-substituted DPP derivatives. Various methods were used to characterise the dyes, including absorption spectroscopy also with polarized light, fluorescence spectroscopy, Langmuir techniques, and time-dependent density functional theory (TD-DFT) calculations. The presented results emphasise a significant impact of side alkyl chains on DPP's molecular behaviour, notably evident in thin-layer structures. Interestingly, the deconvolution of the absorption spectra revealed three bands in the red region. Insightful analysis of temperature-dependent absorption, excitation, and emission fluorescence spectra indicates the co-existence of monomer, dimer, and a higher aggregate forms, most likely a tetrameric structures. Moreover, such a complexity of molecular organisation of dyes appears already in the solution. Differences in spectral properties of the dyes studied are robustly visible in changes in the spectra of the air–water interface, where the dye with the branched side group changes the mutual orientation in dimeric structures, leading to the formation of H-type aggregates, which was observed as an almost 20-nm spectral blue shift during Langmuir layer compression. The results presented highlight the need for care in interpretation of the intensity ratio of DPP spectra and spectral shift as the sole determinants of the aggregation state.

Luminescence and Energy Transfer Properties of Color-Tunable Dy3+, Eu3+ co-Activated NaGdSiO4 Phosphor for WLED with Great Thermo-Stability.

A series of NaGd1-x-ySiO4: y Dy3+-x Eu3+ phosphors were synthesized by a high-temperature solid-phase method. The optimal doping ion concentration of Dy3+ ions for this phosphor was determined to be 1 % from the emission spectra. The energy transfer between Dy3+ and Eu3+ ions at 351 nm was investigated by photoluminescence spectra and fluorescence decay curves. At the excitation wavelengths of 275 nm, 351 nm, 366 nm, and 394 nm, a change from yellow to white to red light can be realized by adjusting the doping concentration of Eu/Dy ions. Particularly, by testing the temperature-dependent fluorescence spectrum of the phosphor, it can be found that the luminous intensity of the phosphor is as high as 96 % when 394 nm excitation is employed at 413 K. It was the maximum at this temperature comparing with other phosphors as far as we know. The color coordinate values show that the NaGd1-x-ySiO4:×Dy3+-y Eu3+ phosphors are very close to the white light color coordinates (x=0.33, y=0.33) under 351 nm excitation. Meanwhile, the correlated color temperature is between 5062-7104 K. These results indicate that this phosphor is a promising candidate for high-quality WLED.

Bisphenol a modification and how its structure influences human serum albumin binding force

Bisphenol A (BPA) is an environmental hormone with substantial physiological toxicity to the human body. Three electron-withdrawing derivatives of BPA are synthesized in this study to reduce its toxicity. The interaction mechanism between BPA and its three derivatives with human serum albumin (HSA) is investigated using molecular docking, electrochemistry, circular dichroism spectrum analysis, and fluorescence spectroscopy. Temperature-dependent tests and time-resolved fluorescence spectra reveal that all four compounds dynamically quench the internal fluorescence of HSA. Based on molecular docking and site competition outcomes, four compounds are primarily bound to site I's active pocket. Thermodynamic parameters indicate that the compounds’ interaction with HSA is spontaneous, and introducing weak electron-withdrawing groups changes the action force. Circular dichroism and synchronous fluorescence measurements suggest four compounds impact HSA's structure. The substituents' electron attraction capacity determines their impact. Electrochemical studies examine the effect of electron-absorbing groups on the BPA and HSA binding capacity. Pharmacokinetics showed that nitro-substituted BPA may be a potential superior substitute for BPA. These results indicate crucial practical value, providing theoretical support for future research.

Efficient monodisperse upconversion composite prepared using high-density local field and its dual-mode temperature sensing.

Enhanced upconversion via plasmonics has considerable potential in biosensors and solar cells; however, conventional plasmonic configurations such as core-shell assemblies or nanoarray platforms still suffer from the compromise between the enhancement factor and monodispersity, which has failed to meet the requirement of the materials for the in vivo all-solution-prepared solar cells and biosensors. We herein report a monodisperse metal-dielectric-metal (MDM) type upconverted hybrid material with high efficiency. The lanthanide-doped upconversion nanoparticles (UCNPs) were sandwiched by two gold nanodisk mirrors, and the highly localized excitation field around the UCNPs together with the efficient coupling enhanced the upconversion. The upconversion intensity can then be effectively regulated and improved by three to four orders of magnitude. As per the measurement of the temperature-dependent fluorescence intensity and spectra shift, a dual-mode nanothermometer based on our proposed hybrid materials was demonstrated. This MDM-type upconverted hybrid material demonstrated the merits of high efficiency and monodispersity, which demonstrated promise in in vivo biosensors and solar cell fabrication techniques such as spin-coating and roll-to-roll.

Effect of nano-SiO2 on performances of KBaYSi2O7: Eu3+ red phosphor for NUV-pumped LEDs

KBaY0.9Si2−xSixO7: 0.1Eu3+ phosphors were prepared by traditional high temperature solid state reaction method at 1050 ℃ with nano and micron SiO2 as raw materials. The particle size of nano-SiO2 is 15, 30 and 50 nm. The crystal structure, morphology, luminescence intensity and thermal stability of the samples were characterized by XRD, SEM, photoluminescence spectra and temperature-dependent fluorescence spectra, respectively. The results show that the phosphor is a single matrix, and the mixing of nano-SiO2 increases the particle size and improves crystallization of the phosphor. KBaY0.9Si0.4Si1.6O7: 0.1Eu3+ mixed by nano-SiO2 with particle size of 15 nm has the improved performance of luminescence intensity enhanced by 13.7 % and thermal stability enhanced by 11 %. CIE coordinates are (0.670, 0.330) and close to the standard redlight source. Therefore, KBaY0.9Si0.4Si1.6O7: 0.1Eu3+ has a broad prospect in red phosphors for NUV excited LEDs.

Highly efficient yellow emission and abnormal thermal quenching in Mn2+-doped Rb4CdCl6.

In this paper, Mn2+-doped Rb4CdCl6 metal halide single crystals were prepared by a hydrothermal method. The Rb4CdCl6:Mn2+ metal halide exhibits yellow emission with photoluminescence quantum yields (PLQY) as high as 88%. Due to the thermally induced electron detrapping, Rb4CdCl6:Mn2+ also displays good anti-thermal quenching (ATQ) behavior with thermal quenching resistance (131% at 220 °C). The increase in the photoionization and the detrapping of the captured electrons from the shallow trap states were appropriately attributed to this exceptional phenomenon based on thermoluminescence (TL) analysis and density functional theory (DFT) calculations. The relationship between the fluorescence intensity ratio (FIR) of the material and temperature change was further explored using the temperature-dependent fluorescence spectrum. It was used as a temperature measuring probe based on absolute sensitivity (Sa) and relative sensitivity (Sb) with the change in temperature. The phosphor-converted white light emitting diodes (pc-WLEDs) were fabricated using a 460 nm blue chip with a yellow phosphor, which has a color rendering index (CRI = 83.5) and a low correlated color temperature (CCT = 3531 K). Because of this, finding new metal halides with ATQ behavior for high-power optoelectronic applications may be made possible by our findings.

Color-tunable hypersensitive temperature sensor based on metal organic framework doped with Eu3+ and Dy3+ via phonon-assisted energy transfer

In this work, catena-[(μ-benzene-1,3,5-tricarboxylato)-(1,10-phenanthroline)-(N,N-dimethylformamide)-gadolinium(iii)-N,N-dimethylformamide solvate] (denoted as Gd-MOF) co-doped with Eu3+ and Dy3+ was successfully synthesized. The entire X-ray diffraction peaks of the sample match well with the Gd-MOF phase. A detailed characterization by inductively coupled plasma mass spectrometry (ICP-MS) shows that the actual concentration is basically consistent with the design concentration. The temperature sensing properties of Gd-MOF:Eu3+,Dy3+ were analyzed by temperature-dependent fluorescence spectra from 213 to 453 K. As temperature rises, the emission color of Gd-MOF:Eu3+,Dy3+ changes from yellow to red. The relative sensitivity reaches a maximum of 5.87%/K at 383 K in the Gd-MOF:1%Eu3+,30%Dy3+ sample. The high relative sensitivity of this MOF is due to the phonon-assisted energy transfer from Dy3+ to Eu3+, which is proved via fluorescence decay curves and fluorescence spectra. The major route of this energy transfer is 4F9/2(Dy3+) →5D1(Eu3+).

Monitoring lipid phase transition temperatures using fluorescent probes and temperature-dependent fluorescence spectroscopy

The response of fluorescent dyes incorporated in multilamellar liposomes was evaluated for their applicability in monitoring thermal-induced changes in liposomes. Five fluorescent probes, diverse in polarity, lipophilicity, and consequently their position within the lipid multibilayers constituted from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), were used to record temperature-dependent fluorescence spectra of the liposomal suspensions. The responses of the dyes were analysed in a multivariate fashion to determine pre- and main phase transition temperatures of DPPC. Laurdan® and 1-chloro-9,10-bis(phenylethynyl)anthracene register both phase transitions, while 9,10-diphenylanthracene and 9,10-bis(phenylethynyl)anthracene report only pretransition. According to the differential scanning calorimetry (DSC) measurements, all suspensions display both phase transitions that resemble DSC curve of pure DPPC. The positions of the dyes within the bilayers were determined by molecular dynamics simulations.

Reversible mechanochromic studies on AIE-inspired smart materials and their applications in HCHO sensing.

Smart fluorescent materials that respond to external stimuli have received more and more attention because of their excellent optical properties in the field of anti-counterfeiting, information security and fluorescence sensing. Herein, we reported a new stimulus-responsive material, {[Zn4(TCPE)(HTCPE)(DMA)3(OH)(H2O)2]·2DMA·2H2O}n (HPU-21), which showed a series of fluorescence changes under the influence of temperature, pressure and solvents. Combined with the temperature-dependent fluorescence, 1H NMR and 13C NMR spectra, TEM and powder X-ray diffraction results, the fluorescence transformation was mainly attributed to the changes in the twisted ethyl core and the multiple rotational phenyl rings, as well as the aggregation degree. Based on these findings, we designed an adjustable formaldehyde probe with excellent performance. The detection limit of formaldehyde in aqueous solutions is calculated as 35 ppb, which is much lower than the concentration that is harmful to health (20 ppm). The extremely high sensitivity to formaldehyde makes it have potential application prospects in practical formaldehyde detection.

Highly sensitive temperature sensing of compound of CsPbBr3 perovskite quantum dots and NaYF4:Ho3+ nanoparticles

Dual-phase compounds consisting of CsPbBr3 perovskite quantum dots (PQDs) and NaYF4:Ho3+ nanoparticles (NPs) were prepared, and their phase compositions and luminescence properties were characterized. The temperature-dependent fluorescence spectra of compounds were measured under 447 nm excitation in the temperature range from 123 K to 433 K. With the increase of temperature, the fluorescence intensities of PQDs and NPs show different decreasing trends due to different temperature quenching mechanisms. Then, the temperature sensing properties of compounds are studied via fluorescence intensity ratios (FIRs) of 529 nm (CsPbBr3) to 647 nm and 751 nm (NaYF4:Ho3+). The result shows that I529/I751 owns super large absolute sensitivity (385 K−1), high relative sensitivity (5.13%∙K−1) and distinct optimum temperature uncertainty (0.00345 K). Therefore, this compound may be used as highly sensitive temperature sensors.

Characterization of tracers for two-color laser-induced fluorescence thermometry of liquid-phase temperature in ethanol, 2-ethylhexanoic-acid/ethanol mixtures, 1-butanol, and o-xylene.

The fluorescence spectra of dye solutions change their spectral signature with temperature. This effect is frequently used for temperature imaging in liquids and sprays based on two-color laser-induced fluorescence (2cLIF) measurements by simultaneously detecting the fluorescence intensity in two separate wavelength channels resulting in a temperature-sensitive ratio. In this work, we recorded temperature-dependent absorption and fluorescence spectra of solutions of five laser dyes (coumarin 152, coumarin 153, rhodamine B, pyrromethene 597, and DCM) dissolved in ethanol, a 35/65 vol.% mixture of ethanol/2-ethylhexanoic acid, ethanol/hexamethylsiloxane, o-xylene, and 1-butanol to investigate their potential as temperature tracers in evaporating and burning sprays. The dissolved tracers were excited at either 266, 355, and 532 nm (depending on the tracer) for temperatures between 296 and 393 K (depending on the solvent) and for concentrations ranging between 0.1 and 10 mg/l. Absorption and fluorescence spectra of the tracers were investigated for their temperature dependence, the magnitude of signal re-absorption, the impact of different solvents, and varying two-component solvent compositions. Based on the measured fluorescence spectra, the tracers were analyzed for their 2cLIF temperature sensitivity in the respective solvents. Coumarin 152 showed for single-component solvents the overall best spectroscopic properties for our specific measurement situation related to temperature imaging measurements in spray-flame synthesis of nanoparticles as demonstrated previously in ethanol spray flames [Exp. Fluids61, 77 (2020)10.1007/s00348-020-2909-9].

Spectroscopic characterization of low-phonon Er-doped BaF2 single crystal for mid-IR lasers

We present spectroscopic properties of the low-maximum-phonon energy host material, barium fluoride (BaF2) doped with Er3+ ions. Following optical excitation at 800 nm, Er3+:BaF2 exhibited broad mid-IR emission bands centered at ∼2.75, ∼3.5, and ∼4.5 µm, corresponding to the 4I11/2 → 4I13/2, 4F9/2 → 4I9/2 and 4I9/2 → 4I11/2 transitions, respectively. Temperature-dependent fluorescence spectra and decay times were recorded for the 4I9/2 level, which was resonantly excited at ∼800 nm. The multi-phonon decay rates of several closely spaced Er3+ transitions were derived using the well-known energy-gap law, and the host-dependent energy-gap law parameters B and α were determined to be 9.15 × 108 s−1 and 5.58 × 10−3 cm, respectively. The obtained parameters were subsequently used to describe the temperature dependence of the ∼4.5 µm mid-IR emission lifetime in a temperature range of 12 - 300 K. The stimulated emission cross-section of the 4I9/2 → 4I11/2 transition of Er3+ ion was derived for the first time among the known fluoride hosts, to the best of our knowledge, and found to be 0.11 × 10−20 cm2 at room temperature and 0.21 × 10−20 cm2 at 77 K.

Using temperature dependent fluorescence to evaluate singlet fission pathways in tetracene single crystals.

The temperature-dependent fluorescence spectrum, decay rate, and spin quantum beats are examined in single tetracene crystals to gain insight into the mechanism of singlet fission. Over the temperature range of 250 K-500 K, the vibronic lineshape of the emission indicates that the singlet exciton becomes localized at 400 K. The fission process is insensitive to this localization and exhibits Arrhenius behavior with an activation energy of 550 ± 50 cm-1. The damping rate of the triplet pair spin quantum beats in the delayed fluorescence also exhibits an Arrhenius temperature dependence with an activation energy of 165 ± 70 cm-1. All the data for T > 250 K are consistent with direct production of a spatially separated 1(T⋯T) state via a thermally activated process, analogous to spontaneous parametric downconversion of photons. For temperatures in the range of 20 K-250 K, the singlet exciton continues to undergo a rapid decay on the order of 200 ps, leaving a red-shifted emission that decays on the order of 100 ns. At very long times (≈1 µs), a delayed fluorescence component corresponding to the original S1 state can still be resolved, unlike in polycrystalline films. A kinetic analysis shows that the redshifted emission seen at lower temperatures cannot be an intermediate in the triplet production. When considered in the context of other results, our data suggest that the production of triplets in tetracene for temperatures below 250 K is a complex process that is sensitive to the presence of structural defects.

Enhanced solubility of bisdemethoxycurcumin by interaction with Tween surfactants: Spectroscopic and coarse-grained molecular dynamics simulation studies

The oral bioavailability of bisdemethoxycurcumin, one of the main active compounds of curcuminoids, can be improved by the encapsulation of surfactant micelles. The interaction of bisdemethoxycurcumin with Tween 20 and Tween 60 micelles was investigated by spectroscopic techniques and molecular dynamics simulation. The binding parameters were obtained from temperature-dependent fluorescence and absorption spectra. The main driving forces were inferred from the enthalpic and entropic contributions. The binding site and surrounding microenvironment of bisdemethoxycurcumin in Tween micelles were evaluated. Coarse-grained molecular dynamics simulations confirmed the binding of bisdemethoxycurcumin with Tween micelles from the microscopic perspective. The influence of different alkyl chains of Tween 20 and Tween 60 on their interaction with bisdemethoxycurcumin and their solubilization capability toward bisdemethoxycurcumin was discussed. These results suggested that Tween 20 and Tween 60, especially Tween 60, can be used as carriers for encapsulating bisdemethoxycurcumin to increase its aqueous solubility.

Double-Stranded DNA Matrix for Photosensitization Switching

Photosensitization, originated from the activation of triplet states, is the basis of many photodynamic applications, but often competes with a series of nonradiative processes. Herein, we communic...

Toward high-efficiency photoluminescence emission by fluorination of graphene oxide: Investigations from excitation to emission evolution

Graphene oxide (GO) alters zero bandgap of graphene to achieve photoluminescence (PL), while the low quantum yield (generally: PLQY < 1%) seriously restricts its further development in practical applications. Here we employ two-step fluorination strategy to controllably modify GO, achieving island structure of aromatic regions in continuous phase of fluorine regions. The fluorinated product (FGO) presents a high PLQY of 66%, far exceeding the largest value (21.2%) reported for modifications of GO. We systematically and meticulously investigate fluorine effect of FGO during whole PL evolution. In excitation process, the coexistence of fluorine and aromatic regions in FGO is responsible for new electronic bandgap structure then multitudinous excited electrons produce, thus providing foundation for strong PL. In emission process, Raman measurements show that the weaker electron-phonon interactions in FGO result in slower nonradiative decay. It is attributed to that FGO possesses larger rigidity, as demonstrated by temperature-dependent fluorescence spectra, broadband dielectric measurements, density functional theory calculations and infrared spectra. Interestingly, different types of fluorine-related groups in FGO play different roles. That is, unoriented CF2 and CF3 groups realize passivation of defects, and C–F bonds perpendicular to graphene plane contribute to weakening interlayer interactions, both greatly enhancing PL.

Interaction of Chlorophyll with Titanium Dioxide and Iron Oxide Nanoparticles: A Temperature Dependent Fluorescence Quenching Study

This study explores the temperature-dependent interaction of chlorophyll with titanium dioxide and iron oxide nanoparticles using steady-state and time-resolved laser-induced fluorescence spectroscopy. For this work, temperature-dependent steady-state fluorescence spectra of chlorophyll and chlorophyll mixed with titanium dioxide and iron oxide nanoparticles have been recorded in spectral region from 400 to 800 nm. The scrutiny of the spectra reveals that the titanium dioxide and iron oxide nanoparticles decrease the fluorescence intensity of the chlorophyll band at 669 nm demonstrating the quenching of the chlorophyll fluorescence. The deviation from linearity and upward curvature of Stern-Volmer plot of the chlorophyll-titanium dioxide nanoparticles shows involvement of both static and dynamic quenching while the straight line plot obtained in case of the chlorophyll-iron oxide nanoparticles indicates the involvement of either static quenching or dynamic quenching. The measurements obtained from time resolved fluorescence analysis reveal that the lifetime of chlorophyll does not change significantly with increasing concentrations of the titanium dioxide and iron oxide nanoparticles. This relationship shows the predominance of static quenching mechanism in the chlorophyll-titanium dioxide and chlorophyll-iron oxide nanoparticles interaction. The binding constant for the chlorophyll-titanium dioxide nanoparticles and chlorophyll-iron oxide nanoparticles decreases with increasing temperature having only one binding site with negative values of thermodynamic quantities such as the changes in enthalpy and entropy, indicating the involvement of hydrogen bonding and van der Waals forces in the quenching process. The energy-level diagram shows that the quenching of fluorescence forces due to electron transfer from the excited state chlorophyll to the conduction band of the titanium dioxide and iron oxide nanoparticles. The results obtained in this study are useful in characterizing the photophysical properties of the semiconducting metal oxide nanoparticles with biological molecules such as chlorophyll.

Investigation of Five Organic Dyes in Ethanol and Butanol for Two-Color Laser-Induced Fluorescence Ratio Thermometry

In this article, we compare absorption and temperature-dependent fluorescence spectra of five organic dyes for 2c-LIF (two-color laser-induced fluorescence) thermometry in ethanol and butanol. The dyes fluorescein, eosin Y, rhodamine B, rhodamine 6G, and sulforhodamine 101 individually mixed in ethanol and butanol were studied at liquid temperatures of 25–65 °C. The self-absorption spectral bands are analyzed along with intensity ratios and the respective sensitivities for one-dye and two-dye 2c-LIF thermometry are deduced. For one-dye 2c-LIF, rhodamine B showed the highest sensitivity of 2.93%/°C and 2.89%/°C in ethanol and butanol, respectively. Sulforhodamine 101 and rhodamine 6G showed the least sensitivities of 0.51%/°C and 1.24%/°C in ethanol and butanol, respectively. For two-dye 2c-LIF, rhodamine B/sulforhodamine 101 exhibited the highest temperature sensitivities of 2.39%/°C and 2.54%/°C in ethanol and butanol, respectively. The dye pair eosin Y/sulforhodamine 101 showed the least sensitivities of 0.15%/°C and 0.27%/°C in ethanol and butanol, respectively.

Fluorescence enhancement of organic chromophore in solid state via organic–inorganic hybrid matrix: Steady state and kinetic studies

Xerogels of silica-based organic–inorganic hybrid materials consisting of covalently bound fluorophores, terthiophene and terphenylene derivatives, were fabricated and analyzed. The synthesized chromophore-containing alkoxysilane derivatives were no emission in solid state, but showed strong fluorescence in organic–inorganic hybrid materials as well as in solution. Moreover, the fluorescence quantum yield of chromophore could be further improved in organic–inorganic hybrid materials with the optimized component than that of chromophore dissolved in solution. On the other hand, the fluorescence intensity of hybrid materials decreased with increasing the concentration of chromophore in organic–inorganic hybrid materials. Obviously, the relative distance between chromophores was shortened to perturb radiative relaxation. Temperature-dependent fluorescence spectra revealed that the fluorescence of chromophore in organic–inorganic hybrid materials was temperature-independent. This result indicated the inter-chromophore interactions and intra-molecular motion have been forbidden. The kinetic measurements confirmed that the chromophore spread in organic–inorganic hybrid materials was fixed with rigid conformation. The florescence decay lifetime of chromophore also kept similar at different temperature with organic–inorganic hybrid materials skeleton. This hybrid matrix provided a platform that enhanced fluorescence of chromophore in solid state at ambient temperature. Emission enhancement of organic chromophores, terthiophene and terphenylene, was performed through the utilization of covalently bound silica-based organic–inorganic hybrid material (OIHM). The chromophore was no emission in solid state, but showed strong fluorescence in OIHM as well as in solution. Moreover, the fluorescence quantum yield of chromophore could be better in OIHM with optimized component than that in solution. Temperature-dependent fluorescence spectra revealed that the fluorescence of chromophore in OIHM was temperature-independent. The kinetic measurements confirmed that the chromophore spread in OIHM was fixed with rigid conformation. This OIHM system offered a useful platform to maintain the emission behavior of organic chromophores in quasi-solid state.

Temperature dependent fluorescence spectra arise from change in excited-state intramolecular proton transfer potential of 4′-N,N-dimethylamino-3-hydroxyflavone-doped acetonitrile crystals

The effect of intermolecular interaction on excited-state intramolecular proton transfer (ESIPT) in 4′-N,N-dimethylamino-3-hydroxyflavone (DMHF) doped in acetonitrile crystals was investigated by measuring the temperature dependence of fluorescence excitation and fluorescence spectra. A solid/solid phase transition of DMHF-doped acetonitrile crystals occurred in the temperature between 210 and 218K. Significant differences in the spectral profiles and shifts in the fluorescence spectra were observed in the low- and high-temperature regions of the phase transition. The temperature dependence of the ESIPT potential of DMHF is discussed.