Temperature Dependence Of Fluorescence Spectra Research Articles

Structural and spectroscopic characterization of two new layered uranyl(VI) p-xylenediphosphonate compounds synthesized via ionothermal method

Two new uranyl phosphonates were synthesized by using p-xylenediphosphonic acid (pmbH4) to react with uranyl salts in Emim or BMMim ([EMim][PF6]=1-ethyl-3-methylimidazolium hexafluorophosphate; [BMMim]Cl=1-butyl-2,3-dimethylimidazolium chloride) at elevated temperature, namely [EMim][UO2(pmbH2)0.5(pmbH2)0.5(ox)0.5] (1) and [BMMim]2[(UO2)2(pmbH2)(pmb)] (2). Both compounds adopt two dimensional structures, consisting of an anionic layer of uranyl phosphonate, with cations filled in the interlayer spaces. The spectroscopic properties of the compounds were studied extensively using UV–Vis absorption, temperature dependent fluorescence, Raman and IR spectroscopies. The UV–Vis absorption spectrum contains typical peaks of uranyl complexes at around 320nm and 420nm, which are originated from the charge transfer transitions from O 2p orbitals to the U 5f/6d orbitals. Both compounds adopt five strong emission peaks, whose intensities increase with the decrease of temperature, as observed in the temperature dependent fluorescence spectra. In Raman and IR spectra, the peaks corresponding to the stretch of C–H/O–H, P–O/PO, and OUO bonds could all be located and assigned.

A cationic fluorescent polymeric thermometer for the ratiometric sensing of intracellular temperature.

We developed new cationic fluorescent polymeric thermometers containing both benzothiadiazole and BODIPY units as an environment-sensitive fluorophore and as a reference fluorophore, respectively. The temperature-dependent fluorescence spectra of the thermometers enabled us to perform highly sensitive and practical ratiometric temperature sensing inside living mammalian cells. Intracellular temperatures of non-adherent MOLT-4 (human acute lymphoblastic leukaemia) and adherent HEK293T (human embryonic kidney) cells could be monitored with high temperature resolutions (0.01-1.0 °C) using the new cationic fluorescent polymeric thermometer.

Temperature-dependent Mollow triplet spectra from a single quantum dot: Rabi frequency renormalization and sideband linewidth insensitivity.

We investigate temperature-dependent resonance fluorescence spectra obtained from a single self-assembled quantum dot. A decrease of the Mollow triplet sideband splitting is observed with increasing temperature, an effect we attribute to a phonon-induced renormalization of the driven dot Rabi frequency. We also present first evidence for a nonperturbative regime of phonon coupling, in which the expected linear increase in sideband linewidth as a function of temperature is canceled by the corresponding reduction in Rabi frequency. These results indicate that dephasing in semiconductor quantum dots may be less sensitive to changes in temperature than expected from a standard weak-coupling analysis of phonon effects.

Effect of Substrates on the Temperature Dependence of Fluorescence Spectra of Nitrogen Vacancy Centers in Diamond Nanocrystals

Effect of Substrates on the Temperature Dependence of Fluorescence Spectra of Nitrogen Vacancy Centers in Diamond Nanocrystals

Effect of Substrates on the Temperature Dependence of Fluorescence Spectra of Nitrogen Vacancy Centers in Diamond Nanocrystals

The temperature dependence of fluorescence spectra of nitrogen vacancy (NV) centers in diamond nanocrystals is investigated in terms of the ability of the substrate to suppress the fluorescence phonon sideband of negatively charged NV (NV-) centers. Three substrates were used: a glass coverslip, undoped silicon (Si), and thermally oxidized silicon (SiO2/Si). Nanocrystals were distributed on these substrates and the temperature dependence of fluorescence spectra of NV- centers of individual nanocrystals were measured in the temperature range 3.5–230 K. We found that the zero-phonon line (ZPL) of NV- centers in nanocrystals on the SiO2/Si substrate remained intense as the temperature was increased from 3.5 to 160 K, whereas it monotonically decreased for the Si substrate. Diamond nanocrystals dispersed on a glass coverslip did not exhibit prominent ZPLs of NV- centers, even at 3.5 K. The temperature dependencies of the peak intensities of NV- centers were quantitatively analyzed by determining the Debye–Waller factors of the three substrates. As the temperature was increased from 3.5 to 230 K, the Debye–Waller factor decreased almost linearly from 10 to 1.7% for the SiO2/Si substrate, decreased from 6.1 to 1.6% for the Si substrate, and decreased from 0.9 to 0.62% for the glass coverslip. These results will be useful for nanophotonic device applications of nanodiamond NV centers in quantum information science and sensing.

Following G-quadruplex formation by its intrinsic fluorescence

We characterized and compared the fluorescence properties of various well-defined G-quadruplex structures. The increase of intrinsic fluorescence of G-rich DNA sequences when they form G-quadruplexes can be used to monitor the folding and unfolding of G-quadruplexes as a function of cations and temperature. The temperature-dependent fluorescence spectra of different G-quadruplexes also exhibit characteristic patterns. Thus, the stability and possibly also the structure of G-quadruplexes can be characterized and distinguished by their intrinsic fluorescence spectra.

Parallelly and Normally Surface-Aligned Organic Nanofiber Arrays

Results are presented from a direct comparison of 2,7-diphenylcarbazole (DPC) nanofibers fabricated in the form of parallel to the surface plane aligned arrays by means of organic molecular beam deposition (OMBD) and fabricated in the form of normal to the surface aligned arrays by solution-assisted wetting of porous anodic alumina (PAA) membranes. The former method leads to the formation of mutually aligned needlelike nanoaggregates on muscovite mica substrates, while the latter method allows fabrication of arrays of closely packed upright standing nanofibers. The dimensions of the DPC nanofibers obtained by the OMBD technique depend strongly on the nominal film thickness and on the substrate temperature during deposition. The DPC nanofibers obtained by template wetting possess the same shape and dimensions as those of the pores of the PAA template. All of the obtained nanofibers show strong polarization anisotropy, but the polarization dependent measurements indicate a higher degree of mutual alignment of the DPC molecules in the fibers obtained by OMBD as compared to those obtained by membrane wetting. Temperature dependent fluorescence spectra from the DPC nanoaggregates reveal blue shifts and narrowing of the spectral peaks with decreasing temperature as well as a redistribution of peak intensities.

π-Conjugated oligothiophene–anthracene co-oligomers: synthesis, physical properties, and self-assembly

A new class of oligothiophene–anthracene co-oligomers, 9,10-bis(2-dodecyloligothienylvinyl)anthracene TnA (n = 1, 2 and 3), were synthesized and characterized. The photophysical and electrochemical properties of these oligomers demonstrated an increased conjugation length with increasing number of thiophene units. These oligomers also exhibited relatively larger ionization potential values compared with pentacene and sexithiophene and thus are expected to show improved stability. The strong aggregation tendency and excimer formation for T1A and obvious aggregation effect for T2A in solution were observed from the concentration and temperature-dependent fluorescence spectra. In contrast, no obvious aggregation behavior could be observed for T3A in solution. Thermal behavior and self-assembly of these co-oligomers in solid state were studied by a combination of TGA, DSC, powder X-ray diffraction and polarizing optical microscope. Liquid crystalline phases were observed in T2A and T3A at elevated temperature while only a crystalline phase was found for T1A. Single-crystal structures of T1A and T2A revealed a lamellar packing mode with ordered intermolecular anthracene-to-anthracene and oligothiophene-to-oligothiophene π–π stacking and these qualify them as potential semiconductors in electronic devices.

Separation and Analysis of Dynamic Stokes Shift with Multiple Fluorescence Environments: Coumarin 153 in Bovine β-Lactoglobulin A

We use time-dependent fluorescence Stokes shift (TDFSS) information to study the fluctuation rates of the lipocalin, beta-lactoglobulin A in the vicinity of an encapsulated coumarin 153 molecule. The system has three unique dielectric environments in which the fluorophore binds. We develop a method to decompose the static and dynamic contributions to the spectral heterogeneity. This method is applied to temperature-dependent steady-state fluorescence spectra providing us with site-specific information about thermodynamic transitions in beta-lactoglobulin. We confirm previously reported transitions and discuss the presence of an unreported transition of the central calyx at 18 degrees C. Our method also resolves the contributions to the TDFSS from the coumarin 153 centrally located in the calyx of beta-lactoglobulin despite overlapping signals from solvent exposed dyes. Our experiments show dynamics ranging from 3-12,00 ps. The analysis shows a decrease in the encapsulated dye's heterogeneity during the relaxation, which is taken as evidence of the breakdown of linear response.

Mathematical and Computational Models for Transport and Coupled Processes in Micro- and Nanotechnology

To synthesize composite solid materials of metal salt and CdSe nanocrystals by a simple one-step method has been described. These solids can form stable gel in some organic solvent, such as benzene, cyclohexane and 1-butanol, especial in n-decane even below 0.1 wt/vol.%. Furthermore, these gels appear strong fluorescence which can be easily adjusted by the gel concentration. Temperature-dependent fluorescence spectra of composite gels suggested that the CdSe NCs aggregate together in gel state which would induce the energy transfer between nanocrystals and these aggregates could be reversibly disintegrated when gel was heated to form sol. TEM observations provided the further evidence of the energy transfer and suggested that the CdSe NCs were enchased regularly not only on the surface of self assembly of metal salt, but also embedded inside of self assembly in composite gel with small size nanocrystals. In contrast, in composite organogel with large nanocrystals they were only enchased on the edge of self assembly.

Reversible and Hierarchical Composite Gels with CdSe Nanocrystals

To synthesize composite solid materials of metal salt and CdSe nanocrystals by a simple one-step method has been described. These solids can form stable gel in some organic solvent, such as benzene, cyclohexane and 1-butanol, especial in n-decane even below 0.1 wt/vol.%. Further-more, these gels appear strong fluorescence which can be easily adjusted by the gel concentration. Temperature-dependent fluorescence spectra of composite gels suggested that the CdSe NCs aggregate together in gel state which would induce the energy transfer between nanocrystals and these aggregates could be reversibly disintegrated when gel was heated to form sol. TEM observations provided the further evidence of the energy transfer and suggested that the CdSe NCs were enchased regularly not only on the surface of self assembly of metal salt, but also embedded inside of self assembly in composite gel with small size nanocrystals. In contrast, in composite organogel with large nanocrystals they were only enchased on the edge of self assembly.

Stabilization and rovibronic spectra of the T-shaped and linear ground-state conformers of a weakly bound rare-gas–homonuclear dihalogen complex: He⋯Br2

Laser-induced fluorescence spectra of Br(2) entrained in a He supersonic expansion have been recorded in the Br(2) B-X, 8-0, 12-0, and 21-0 spectral regions at varying downstream distances, and thus different temperature regimes. Features associated with transitions of the T-shaped and linear He...Br(2)(X,nu(") = 0) complexes are identified. The changes in the relative intensities of the T-shaped and linear features with cooling in the expansion indicate that the linear conformer is energetically more stable than the T-shaped conformer. A He + Br(2)(X,nu(") = 0) ab initio potential-energy surface, computed at the coupled cluster level of theory with a large, flexible basis set, is used to calculate the binding energies of the two conformers, 15.8 and 16.5 cm(-1) for the T-shaped and linear complexes, respectively. This potential and an excited-state potential [M. P. de Lara-Castells, A. A. Buchachenko, G. Delgado-Barrio, and P. Villareal, J. Chem. Phys. 120, 2182 (2004)] are used to calculate the excitation spectra of He...(79)Br(2)(X,nu(") = 0) in the Br(2) B-X, 12-0 region. The calculated spectra are used to make spectral assignments and to determine the energies of the excited-state intermolecular vibrational levels accessed in the observed transitions. Temperature-dependent laser-induced fluorescence spectra and a simple thermodynamic model [D. S. Boucher, J. P. Darr, M. D. Bradke, R. A. Loomis, and A. B. McCoy, Phys. Chem. Chem. Phys. 6, 5275 (2004)] are used to estimate that the linear conformer is 0.4(2) cm(-1) more strongly bound than the T-shaped conformer. Two-laser action spectroscopy experiments reveal that the binding energy of the linear He...(79)Br(2)(X,nu(") = 0) conformer is 17.0(8) cm(-1), and that of the T-shaped He...(79)Br(2)(X,nu(") = 0) conformer is then 16.6(8) cm(-1), in good agreement with the calculated values.

Assignment of the low-temperature fluorescence in oxygen-evolving Photosystem II

Low-temperature absorption and fluorescence spectra of fully active cores and membrane-bound PS II preparations are compared. Detailed temperature dependence of fluorescence spectra between 5 and 70 K are presented as well as 1.7-K fluorescence line-narrowed (FLN) spectra of cores, confirming that PS II emission is composite. Spectra are compared to those reported for LHCII, CP43, CP47 and D1/D2/cytit b559 subunits of PS II. A combination of subunit spectra cannot account for emission of active PS II. The complex temperature dependence of PS II fluorescence is interpretable by noting that excitation transfer from CP43 and CP47 to the reaction centre is slow, and strongly dependent on the precise energy at which a 'slow-transfer' pigment in CP43 or CP47 is located within its inhomogeneous distribution. PS II fluorescence arises from CP43 and CP47 'slow-transfer' states, convolved by this dependence. At higher temperatures, thermally activated excitation transfer to the PS II charge-separating system bypasses such bottlenecks. As the charge-separating state of active PS II absorbs at >700 nm, PS II emission in the 680-700 nm region is unlikely to arise from reaction centre pigments. PS II emission at physiological temperatures is discussed in terms of these results.

Temperature dependent fluorescence in disordered Frenkel chains: interplay of equilibration and local band-edge level structure.

We model the optical dynamics in linear Frenkel exciton systems governed by scattering on static disorder and lattice vibrations and calculate the temperature dependent fluorescence spectrum and lifetime. The fluorescence Stokes shift shows a nonmonotonic behavior with temperature, which derives from the interplay of the local band-edge level structure and thermal equilibration. The model yields excellent fits to experiments performed on linear dye aggregates.

Temperature Dependence of Fluorescent Probes for Applications to Polymer Materials Processing

We have examined the temperature dependence of fluorescence spectra from dyes that can be used as molecular probes during polymer processing. The dyes, perylene and benzoxazolyl stilbene, are in a class of dyes called band definition dyes, so called because their fluorescence spectra contain distinct intensity peaks at characteristic wavelengths. The dyes were chosen for this study because they are soluble at dopant levels of concentration in organic polymers at elevated temperatures and they survive without degradation at polymer processing temperatures up to 300 °C. Changes induced in the fluorescence spectra over a range of typical processing temperatures were examined using statistical techniques that establish correlations between fluorescence intensity, wavelength, and temperature. The derived correlations are the basis for temperature calibrations that can be applied to process monitoring. A phenomenological model that assumes temperature dependence for both nonradiative and radiative decay modes is developed. A fit of the model parameters to the fluorescence spectra yielded activation energies for the temperature dependence of fluorescence decay rates.

Electron−Phonon Coupling in Solubilized LHC II Complexes of Green Plants Investigated by Line-Narrowing and Temperature-Dependent Fluorescence Spectroscopy

Line-narrowed and temperature-dependent fluorescence spectra are reported for the solubilized trimeric light-harvesting complex of Photosystem II (LHC II). Special attention has been paid to eliminate effects owing to reabsorption and to ensure that the line-narrowed fluorescence spectra are virtually unaffected by hole burning or scattering artifacts. Analysis of line-narrowed fluorescence spectra at 4.2 K indicates that the lowest Qy-state of LHC II is characterized by weak electron−phonon coupling with a Huang−Rhys factor of ∼ 0.9 and a broad and strongly asymmetric one-phonon profile with a peak frequency ωm of 15 cm-1 and a width of Γ = 105 cm-1. The 4.2 K fluorescence data are further consistent with the assignment of the lowest Qy-state at ∼ 680.0 nm and an inhomogeneous width of ∼80 cm-1 gathered from a recent hole-burning study (Pieper et al. J. Phys. Chem. A 1999, 103, 2412). The temperature dependence of the fluorescence spectra of LHC II is simulated using the low-energy Qy-level structure reported in the latter study as well as the parameters of electron−phonon coupling determined in the present study. Up to a temperature of 120 K, the calculations reveal that this model satisfactorily describes the basic features of the fluorescence spectra such as thermal broadening and, especially, the blue-shift of the fluorescence peak with increasing temperature. An unexpected red-shift of the fluorescence peak above 150 K is attributed to conformational changes of the protein environment. The shape of the temperature-dependent fluorescence spectra indicates that the low-energy Qy-states are populated according to a Boltzmann distribution representing the thermal equilibrium of excitation energy.

Temperature variation of near-infrared emission from Cr4+ in aluminate glass for broadband telecommunication

Temperature dependence of fluorescence spectra of Cr4+ in an aluminate glass in the range of 1.2–1.6 μm was investigated from 15 to 300 K. The emission spectra were broadband centered at about 1.3 μm, wider than 200 nm width. The emission intensity drastically increased with decreasing temperature and that of 15 K was 20 times larger than that of 300 K. The bandwidth and mean energy of the emission band changed very slightly with temperature. The emission of Cr4+ in the glass fiber is expected as a tunable laser source and a broadband amplifier for the wavelength-division-multiplexed telecommunication.

ATP's Impact on the Conformation and Holoenzyme Formation in Relation to the Regulation of Brain Glutamate Decarboxylase

To investigate ATP as a potential factor in the regulation of brain glutamate decarboxylase (GAD), the impact of ATP on the enzyme conformation and holoenzyme formation was investigated. ATP at 100 μM quenches fluorescence emission intensity of the holoenzyme of GAD (holoGAD) by 18% after a correction for the inner filter effect and enhances fluorescence steady-state polarization from 0.158 to 0.183 when excited at 280 or 295 nm. These findings suggest that ATP moderately changes the microenvironment of one or more tryptophan or tyrosine residues in holoGAD and alters these residues from a more mobile state to a less mobile one. A moderate ATP-induced conformational change in holoGAD is also supported by the observations that ATP increases the thermal denaturation temperature of holoGAD by 2°C, as derived from temperature-dependent fluorescence spectra, and decreases the α-helical content of holoGAD by 8–10%, as determined by circular dichroism. Moreover, ATP does not affect the keto-enol tautomerization of holoGAD and has little or no direct effect on its activity, implying that the ATP interacting domain in holoGAD is not at the active site. Kinetics studies, as demonstrated by stopped-flow fluorescence and UV/visible spectroscopy, demonstrate that formation of holoGAD involves two steps: a fast reaction forming an apoGAD-cofactor intermediate complex, followed by a slow reaction involving the conformational change in the intermediate complex. ATP reduces the rate constant of the fast step to one-third and decreases the rate of the slow step and the intermediate complex formation constant to 60% of their original values. The present data suggest that ATP may regulate the interconversion between apoGAD and holoGAD by interacting with apoGAD rather than holoGAD. By slowing down the rate of intermediate complex formation, ATP reduces the amount of holoGAD formed.

Photophysical properties of cytochromes c-553 and c3 extracted from Desulfovibrio vulgaris Miyazaki

Fluorescence and UV/visible absorption properties were studied on electron carrier proteins cytochromes c-553 and c 3 and their Fe-free forms (Fe-free cytochromes) over wide pH and temperature ranges in comparison with cytochrome c, hemin and microperoxidase-9 (MP-9). Although cytochromes c-553 and c 3 were extracted from the same sulfate-reducing bacterium, their absorption spectra at acidic pH and pH dependence of fluorescence spectra were different. Cytochrome c-553 showed photophysical characteristics similar to cytochrome c. This is attributed to the influence of the ligands of the fifth and sixth positions of the heme iron in cytochromes c-553 and c 3, which was confirmed by the experiments on MP-9. Through the temperature-dependent fluorescence spectrum and time profile, the coexistence of protonated and deprotonated forms of Fe-free cytochromes at neutral pH was observed. The fluorescence in native cytochromes was observed at acidic pH, whereas MP-9 and hemin showed no fluorescence at the same condition.

Temperature-dependent spectroscopy and photophysics of substituted terthiophenes in fluid solution

The temperature-dependent optical and photophysical properties of terthiophene (TT) as well as three substituted terthiophene derivatives, namely 3′,3″-dimethoxy-2,2′:5′,2″-terthiophene (DMOTT), 3′,3″-dimethyl-2,2′:5′,2″-terthiophene (DMTT) and 3′,4′-dihexyl-2,2′:5′,2″-terthiophene (DHTT) in fluid solution are reported. For TT, it is shown that a change of conformation is induced at low temperature giving rise to a red-shift of the absorption band. This conformational change is explained by an increase of the interaction between TT and solvent molecules at low temperatures. Since the relaxed excited singlet state is expected to be nearly planar for this molecule, no shift is observed in the temperature-dependent fluorescence spectra. DMOTT, which is nearly planar in the ground state, also shows a red-shift of its absorption spectrum at low temperatures. This behavior is interpreted in terms of small conformational changes involving the thiophene rings and methoxy groups. For the alkyl-substituted terthiophene derivatives, which are much twisted in their ground states, changes in the absorption spectra are less important because twisted conformers are still present at low temperatures. The potential energy barrier against planarity for these substituted oligothiophenes does seem to be correlated qualitatively to specific solute–solvent molecular interactions at various temperatures. The fluorescence quantum yield ( φ F), at room temperature, is higher for DMOTT but smaller for alkyl-substituted terthiophenes compared to that of TT. As the temperature is lowered, TT and alkyl derivatives show an important increase of φ F while DMOTT does not show any significant changes in its φ F. Fluorescence quantum yields are also reported in an isopentane glass at 77 K. Results show that φ F of TT and DMOTT are higher in the isopentane glass compared to those measured in fluid solution. On the other hand, the alkyl derivatives show an important decrease of their fluorescence quantum yields in the glassy medium. For all the compounds investigated, a regular increase of the fluorescence lifetime is observed as the temperature is lowered.