Temperature Dependence Of Fluorescence Intensity Research Articles

Nonmonotonic temperature dependence of fluorescence intensity of carbon dots in a glycerol solution

The effect of temperature on the fluorescence of carbon dot colloidal solution in glycerol has been studied. The dots were prepared by pyrolysis of a Nile Red laser dye using mesoporous silica as a template. It is established that the temperature dependence of the intensity of dominant emission peak is nontrivial: as the temperature of the solution rises, the initial quenching of the fluorescence is then replaced by its enhancement to the initial value. A three-level model of electronic states is considered, within which the observed temperature dependence of fluorescence is quantitatively described and the energies of nonradiative deactivation and activation of the emissive state are estimated. The nature of the electronic state responsible for the nonradiative activation of the emissive state is discussed. The possible influence of hydrogen bonds in the solute-solvent system on the temperature behavior of the CD fluorescence is also considered. A pronounced solvatochromic effect is noted in the fluorescence spectra of Nile Red based carbon dots in different solvents.

Temperature dependence of the parameters of laser-induced fluorescence and species composition of phytoplankton: The theory and the experiments

The article discusses the opportunity to determine the species composition of a mixture of microalgae by using the temperature dependence of their laser-induced fluorescence (LIF). Experimental temperature dependences of fluorescence were obtained for the following microalgae: Picochlorum maculatum, Dunaliella salina, Chlorella minutissima, Tetraselmis viridis, Porphyridium purpureum, and Rhodomonas salina. It has been shown that the temperature dependence of fluorescence intensity of chlorophyll a in microalgae is reflective of the specific processes in cells of different microalgae species. A mathematical model for the temperature dependence of microalgae fluorescence and its relationship with the processes occurring in microalgae cells when heated has been formulated. The model allows determining the composition of mixtures with sufficient accuracy, as was shown experimentally on test mixtures of microalgae cultures.

Application of laser-induced fluorescence technique in a duct flow with one heated wall

The laser-induced fluorescence technique has been widely used for temperature measurements in liquids. It is based on the temperature dependence of fluorescence intensity of organic dyes like Rhodamines. The fluorescence emissions of Rhodamine B (RhB) and Rhodamine 110 (Rh110) are investigated using a 532 nm pulsed laser. Temperature and dye concentrations as well as optical filters are varied. A setup is qualified for a ratiometric two-color/two-dye (2c/2d) approach and applied in a highly forced convective duct flow with water as the fluid and with one heated wall. The experimental setup is described and results are presented. The two-color/two-dye technique, as compared to a one-color/one-dye technique, was found to give twice as high-temperature sensitivity and approximately one tenth of pulse-to-pulse variations. The technique is used to analyze temperature fields in a turbulent duct flow with one heated wall. Temperature profiles including the thermal boundary layer for varying boundary conditions are presented and analyzed in terms of, e.g., the size of thermal eddies.

Luminescent lanthanide-containing chiral liquid crystalline polymers in the side chain

Luminescent lanthanide-containing chiral liquid crystalline polymers are graft-copolymerised using poly(methylhydrogeno)siloxane (PMHS), crosslinking agent, liquid crystalline monomer and lanthanide complexes. The chemical structures of the monomers are characterised by FTIR, 1 H NMR and elemental analyses. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing less than 9 mol% of the crosslinking units reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. With the introduction of lanthanide complex units, the polymers are enabled with the significant luminescent properties. The temperature dependence of fluorescence intensity was studied in the liquid crystalline phase. The IR imaging shows that the lanthanide complex units evenly distribute in polymers.

Spectroscopy of Nano-Sized Polysilanes Confined by Different Structures of Silica

Four novel nanocomposite films based on poly(di-n-hexylsilane) (PDHS) incorporated into an inorganic matrix having different structure are fabricated. Polymer chains are localized into the nanopores of SiO2 and TiO2 films, between globules of photonic crystals, as well as in the matrix of nano-sized SiO2 particles. Photoelectronic properties of the composites have been studied using fluorescence (FL) and FL decay measurements in a wide temperature range (5–330) K. The temperature dependence of FL intensities enabled us to establish the nature of a conformational structure of polymer chains, as well as to obtain information about the thermochromic transition of confined PDHS and the excitation energy transfer pathways.

Combined use of steady-state fluorescence emission and anisotropy of merocyanine 540 to distinguish crystalline, gel, ripple, and liquid crystalline phases in dipalmitoylphosphatidylcholine bilayers

The various lamellar phases of dipalmitoylphosphadtidylcholine bilayers with and without cholesterol were used to assess the versatility of the fluorescent probe merocyanine 540 through simultaneous measurements of emission intensity, spectral shape, and steady-state anisotropy. Induction of the crystalline phase (Lc') by pre-incubation at 4°C produced a wavelength dependence of anisotropy which was strong at 15 and 25°C, weak at 38°C, and minimal above the main transition (>~41.5°C) or after returning the temperature from 46 to 25°C. The profile of anisotropy values across this temperature range revealed the ability of the probe to detect crystalline, gel (Lβ'), and liquid crystalline (Lα) phases. The temperature dependence of fluorescence intensity was additionally able to distinguish between the ripple (Pβ') and gel phases. In contrast, the shape of the emission spectrum, quantified as the ratio of merocyanine monomer and dimer peaks (585 and 621 nm), was primarily sensitive to the crystalline and gel phases because dimer fluorescence requires a highly-ordered environment. This requirement also explained the diminution of anisotropy wavelength dependence above 25°C. Repetition of experiments with vesicles containing cholesterol allowed creation of a phase map. Superimposition of data from the three simultaneous measurements provided details about the various phase regions in the map not discernible from any one of the three alone. The results were applied to assessment of calcium-induced membrane changes in living cells.PACS Codes: 87.16.dt

β-Cyclodextrin-induced fluorescence enhancement of a thermal-responsive azobenzene modified polydiacetylene vesicles for a temperature sensor

We devised a novel PDA-based model with linear temperature dependence of fluorescence intensity in a wide temperature range, which could be applied as an accurate temperature sensor in chemical or bio-environment due to the biocompatibility of polydiacetylene (PDA) vesicles. The fluorescence intensity was remarkably enhanced after the adding of β-cyclodextrin (β-CD), and the fluorescent signal remained linear proportional to the temperature in the range from 25 °C to 80 °C. Further, photo-controlled inclusion and exclusion reaction of the azobenzene-containing PDA vesicles with β-CD had been used to act as driving force to induce the change of fluorescence intensity for the composite vesicles. Fluorescence spectroscopy and fluorescence microscopy were used to characterize the fluorescence properties of system. Two-dimensional NMR was used to characterize the interaction between cyclodextrin and azobenzene functional groups. Our work provided a novel system that combines photo-chemistry and host–guest chemistry for a photo-stimulus-responsive vesicle and should be valuable in application in PDA-based temperature sensor.

Relationship between the wavelength maximum of a protein and the temperature dependence of its intrinsic tryptophan fluorescence intensity

Proper determination of the temperature dependence of intrinsic tryptophan fluorescence intensity in native and denatured states is an essential prerequisite for extracting the free energy of protein unfolding from the thermal denaturation profile. The most common method employed in determining the temperature dependence of these conformations is through the determination of slopes of pre- and post-transition baselines. However, simulations of protein unfolding profiles suggest that this method does not work for marginally stable proteins. We show herein that the temperature dependence of the fluorescence intensity of N-acetyl tryptophanamide (NATA) in organic solvents and water may be used to represent the temperature dependence of the fluorescence intensity of tryptophan in native and denatured conformations of a protein, respectively. The wavelength of the emission maximum, lambda (max), of N-acetyl tryptophanamide (NATA) in a particular solvent or tryptophan in proteins is related to the temperature dependence (m) of its fluorescence intensity by the equation: m (K(-1)) = (-0.000299 +/- 2.2 x 10(-5) K(-1) nm(-1)) x lambda (max) (nm) + (0.0919 +/- 0.0025 K(-1)).

Confinement and processing effects on glass transition temperature and physical aging in ultrathin polymer films: Novel fluorescence measurements

Fluorescence intensity measurements of chromophore-doped or -labeled polymers have been used for the first time to determine the effects of decreasing film thickness on glass transition temperature, T(g), the relative strength of the glass transition, and the relative rate of physical aging below T(g) in supported, ultrathin polymer films. The temperature dependence of fluorescence intensity measured in the glassy state of thin and ultrathin films of pyrene-doped polystyrene (PS), poly(isobutyl methacrylate) (PiBMA), and poly(2-vinylpyridine) (P2VP) differs from that in the rubbery state with a transition at T(g). Positive deviations from bulk T(g) are observed in ultrathin PiBMA and P2VP films on silica substrates while substantial negative deviations from bulk T(g) are observed in ultrathin PS films on silica substrates. The relative difference in the temperature dependences of fluorescence intensity in the rubbery and glassy states is usually reduced with decreasing film thickness, indicating that the strength of the glass transition is reduced in thinner films. The temperature dependence of fluorescence intensity also provides useful information on effects of processing history as well as on the degree of polymer-substrate interaction. In addition, when used as a polymer label, a mobility-sensitive rotor chromophore is demonstrated to be useful in measuring relative rates of physical aging in films as thin as 10 nm.

Temperature Dependence of the Fluorescence Intensity of 1-Benzyloxy-2-pyridone and Related Compounds

Abstract A quantitative analysis of the temperature dependence of fluorescence intensity of the title compounds in saturated hydrocarbon solvents has revealed that the relevant thermally-activated radiationless process from singlet manifold involves a rotation about the N–O bond in these compounds.

Partial melting of the segment around pseudouridine in yeast 5S RNA

Pseudouridine in yeast 5S RNA was modified with 4-bromomethyl-7-methoxycoumarin(BMC). Temperature dependence of fluorescence intensity was measured at various concentrations of Mg 2+ and K + cations. Hyperchromicity was also measured. At 100mM KCl and 10mM Mg 2+, fluorescence intensity decreased with temperature as free BMC except a plateau at 45°C. Withdrawal of Mg 2+ from the buffer resulted in a large quenching at 20°C and showed a gradual increase of fluorescence intensity with temperature, indicating a partial melting of the segment around pseudouridine. The temperature range agrees with the low melting temperature shown by hyperchromicity. In 10mM KCl solution, the effects are more exaggerated.

Laser-excited infrared fluorescence in oxalyl fluoride. Relaxation in the presence of a low-energy, one-dimensional quasicontinuum

Fluorescence has been observed from various fundamental and combination states of oxalyl fluoride excited by a Q-switched CO/sub 2/ laser. The presence of a low-frequency torsional mode in this molecule provides a one-dimensional quasicontinuum of vibrational levels at energies above the barrier to rotation about the C-C bond. Intermode vibrational relaxation rates in (COF)/sub 2/ are extremely rapid (possibly collisionless). The observed temperature dependence of fluorescence intensity and the overall rapid equilibration in (COF)/sub 2/ suggest a mechanism in which many rovibrational transitions that possess nu/sub 10/ character (e.g., 0 ..-->.. nu/sub 10/, nu/sub 10/ ..-->.. 2 nu/sub 10/, nu/sub x/ ..-->.. nu/sub x/ + nu/sub 10/, etc.) are excited by the laser. 3 figures.

The Interaction of Protic Compounds with Thioindigo

AbstractBy measuring the temperature dependence of fluorescence intensities and lifetimes a principal difference in the quenching behaviour of thioindigo with aliphatic and aromatic protic compounds is observed. From absorption and IR spectra, an interaction in the groundstate between thioindigo and phenol has to be assumed. Using various substituted phenols the influence of α‐electron density on complex formation is shown.

Polarization of chlorotetracycline fluorescence in pancreatic islet cells and its response to calcium ions and D-glucose

Suspensions rich in pancreatic beta-cells were prepared from non-inbred ob/ob-mice, incubated with 10 micrometer-chlorotetracycline, and analysed for fluorescence polarization in a microscope. Throughout the temperature range 16--38 degrees C, fluorescence was enhanced by 5 mM-Ca2+ in the incubation medium; 20 mM-D-glucose decreased the fluorescence measured in the presence of Ca2+. Fluorescence showed a curvilinear negative regression on temperature. The curves were rectified to a virtually ideal degree by Arrhenius transformations of data. Non-parametric testing of differences between linearized regression lines forms the basis for the following conclusions. The temperature-dependence of fluorescence intensity appeared to be smaller for Ca2+-specific signals than for the background fluorescence of chlorotetracycline in Ca2+-deficient cells. D-Glucose significantly diminished the polarization of fluorescence in cells incubated with Ca2+. It is suggested that D-glucose increases the mobility of Ca2+ in beta-cell plasma membranes; this mobility increase may help to explain previously reported effects of D-glucose on 45Ca2+ fluxes and membrane electric potential.

The temperature dependence of saturated amine fluorescence

The temperature dependence of fluorescence intensity of several saturated amines was studied. For “flexible” amines such as triethylamine (TEA), dimethylethylamine (DMEA), triethylemine, tri- n-octylamine (TOA), and N-methylpiperidine (NMP), it was found that I f increased as the temperature was increased. For example, in DMEA, I f increases by a factor of ca. 77 between −100 and 100°C. These results are interpreted in terms of an activated configurational change from the initially-formed (nonfluorescent) state to a relaxed (fluorescent) state in these compounds. Activation energies for these conversions range from about 1.8 kcal/mole for TOA to about 4.3 kcal/mole for TEA. Rigid, bicyclic amines having bridgehead N-atoms such as 1-azabicyclo [2.2.2] octane (ABCO) and its [3.3.3] analog were found to have temperature independent fluorescence intensities. These results were assumed to reflect the difference in energetics between the initially-formed and relaxed states relative to the “flexible” amines.

Oxygen Effect and Temperature Dependence of Fluorescence Intensity in Naphthalene Scintillators

In solution scintillators with molten naphthalene as a solvent, fluorescence quenching by dissolved oxygen and the temperature dependence of light output are studied with excitation by gamma-rays and uv lights. The fluorescent solutes are PPO, BBO, POPOP, QP, DPH and DPS. Dissolved oxygen can be removed rapidly by bubbling nitrogen. Quenching by oxygen is shown to be in competition with energy transfer from solvent to solute. It may be estimated that the lifetime of excited molecules in molten pure naphthalene is increased to almost twice by removal of oxygen. The bubbling of nitrogen increases the fluorescence intensities of practical solutions by 20–40%. The negative temperature coefficients of light output of naphthalene solutions are 2–7×10-3/°C independent of excitation modes. The fluorescence intensities of the solutions equilibrated with air remain almost constant over the temperature range of 80–130°C.

The Significance of the Temperature Dependence of Fluorescence Intensity

For some phosphors the fluorescence intensity increases with increasing temperature, reaches a maximum, and then decreases. This behavior arises from a competition of an increasing absorption for the exciting radiation and thermal quenching of the emitted radiation. However, the slope of the initial rise of fluorescence and the temperature of the maximum also depend rather strongly on the thickness of the sample considered. Thin samples, i.e., those in which the penetrating exciting radiation is not absorbed completely, in comparison with thick samples exhibit a steeper slope and a maximum at higher temperature. If the phosphor is in powder form, the average particle size also influences the slope and the position of the maximum although generally to a lesser degree than the sample thickness. Experimental data are presented for magnesium fluorogermanate and magnesium fluoroarsenate, both activated with manganese.