Time-resolved emission spectra and anisotropy profiles for symmetric diacyl- and dietherphosphatidylcholines

The solvent relaxation behavior of Patman (6-palmitoyl-2-[[2-(trimethylammonium) ethyl]methylamino]naphthalene chloride) was investigated in small unilamellar vesicles composed of symmetric diacyl( 1,2-dipalmitoylphosphatidylcholine; DPPC) and diether lipids (l,2-dihexadecylphosphatidylcholine; DHPC), calculating time-resolved emission spectra (TRES) and correlation functions. Both the steady-state spectra as a function of temperature and excitation wavelength and the TRES of Patman in DPPC are blue-shifted compared to those in DHPC. The solvent relaxation at three temperatures above and below the phase transition is considerably faster in DHPC than in DPPC. As the steady-state anisotropies of Patman and TMA-DPH [l-(4-trimethylammoniumphenyl)-6-phenyl-l,3,5-hexatriene] are similar in both lipids as a function of both temperature and emission wavelength, we conclude that the introduction of ether linkages allows more efficient water penetration in the glycerol region, leading to a more polar environment and therefore faster solvent relaxation of the incorporated dyes. Using a series ofn-(9-anthroyloxy) fatty acids (n = 2, 3, 6, 9, 12; 16-AP), we show that anisotropy profiles can be used to distinguish between noninterdigitated (DPPC) and fully interdigitated (DHPC) gel-phase structures. 16-(9Antroyloxy) palmitic acid (16-AP) is an especially useful probe exhibiting pronounced differences in the steady-state anisotropies in non- and fully interdigitated gel phases.     

Fluorescence of horse liver alcohol dehydrogenase using one- and two-photon excitation

We examined the steady-state and time-resolved emission of liver alcohol dehydrogenase resulting from one-photon and two-photon excitation. Previous studies with one-photon excitation revealed that the two nonidentical tryptophan residues display different emission spectra and decay times. The use of two-photon excitation resulted in similar emission spectra, multiexponential intensity decays, time-resolved emission spectra, and anisotropy decays as was observed for one-photon excitation. These results suggest that both nonidentical tryptophan residues are excited to a similar extent for one- and two-photon excitation. However, the limiting anisotropy (r ₀) with two-photon excitation from 585 to 610 nm is below 0.1 and appears distinct from that observed previously forN-acetyl-l-tryptophanamide.Abbreviations LADH liver alcohol dehydrogenase - -NAD⁺ -nicotinamide adenine dinucleotide - OPE one-photon excitation - OPIF one-photon induced fluorescence - TPE two-photon excitation - TCSPC time-correlated single photon counting - TPIF two-photon induced fluorescence     

The Dynamics of Intramolecular Excited State Relaxation of <Emphasis Type="Italic">N</Emphasis>-Anthryl Substituted Pyridinium Cations

N-(1-Anthryl)-2,4,6-trimethyl-pyridinium (I), N-(2-anthryl)-2,4,6-trimethyl-pyridinium (II) and 10-(1-anthryl)-1,2,3,4,5,6,7,8-octahydro-acridinium cations (III) with anomalously high fluorescence Stokes shift have been investigated. Fluorescence kinetics analysis at various temperatures showed that in the range 293–77 K, the radiative deactivation rate constants (k_f) increase by 5.5 to 30 times. The low-temperature time-resolved emission spectra of I–III were found to be consistent with the model: A A^* B^* where A^* is the local excited twisted form and B^* is the relaxed more planar, bent conformer of the molecule. The rate constants of the excited relaxed state formation (k₁) and back reaction (k_–1) of compounds studied were estimated.     

Characterization of the excimers of poly(N-vinylcarbazole) using TRANES

Time-resolved emission spectra (TRES) and time-resolved area normalized emission spectra (TRANES) are exploited to characterize the excimers of poly(N-vinylcarbazole) (PNVC) in toluene and water. The time-resolved study together with the steady state measurements, decipher the fluorescence of the system containing pendant carbazole moieties in the polymer backbone unambiguously. Isoemissive point in the TRANES establishes that there are only two excimers of PNVC, the partially overlapped excimer emitting at high energy and the sandwich type excimer emitting at lower energy, and they are formed exclusively in the photoexcited state. The study substantiates an equilibrium between the two excimers.     

Resolution of multiexponential spectral relaxation of Yt-base by global analysis of collisionally quenched samples

We measured the wavelength-dependent intensity decays of 4,9-dihydro-4,6-dimethyl-9-oxo-1H-imidazo-1,2a-purine (Y_t-base) in propanol to determine the time-resolved emission spectra and rates of spectral relaxation. We found that resolution of the spectral relaxation times was dramatically improved by global analysis of the frequency-domain data with increasing amounts of the collisional quencher CCl₄. Collisional quenching preferentially decreases the longer-lived relaxed component of the emission, thereby increasing the fractional contribution of the incompletely relaxed portion of the emission. The data could not be explained by a single spectral relaxation time, and at least two relaxation times are needed to describe the time-dependent emission center of gravity of Y_t-base.Dedicated to Professor Stefan Paszyc on the occasion of his 70th birthday.     

Excited state complex and electroluminescence in TPD-based single layer device

N-N′-diphenyl-N,N′-(bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine) (TPD), was used to fabricate single layer devices (ITO/TPD/Ca/Al). A near-white emission (CIE coordinate of 0.25, 0.24) is observed in electroluminescence (EL) of the single layer device with prominent emission bands at 400, 475 and 670 nm. Steady state and time-resolved emission spectra of spin-coated and annealed TPD films and TRES and TRANES analysis confirmed that emission at 400 and 475 nm are due to monomer and excimer emission, respectively. The origin of the red emission at 670 nm in EL is discussed.     

葡萄球菌核酸酶蛋白的时间分辨荧光与热力学特性

葡萄球菌核酸酶(SNase)是一种小型球状蛋白,其变体常用来研究蛋白质的折叠过程。不同于之前报道的研究方法和技术手段,采用时间相关单光子计数(TCSPC)及飞秒荧光上转换技术,结合紫外吸收谱和稳态荧光光谱,研究了SNase蛋白变体Δ+PHS和Δ+PHS+I92A的荧光动力学,以及不同温度下蛋白结构与热稳定性的关系,证明蛋白质内色氨酸残基可作为一种内源性探针对蛋白变体的结构折叠和热稳定性进行印证和研究。衰减相关光谱(DAS)表明了两种变体随温度变化的不同趋势,在此基础上进一步分析了这两种变体的结构折叠及热稳定性的差异。皮秒时间分辨发射光谱(TRES)显示色氨酸残基存在0.5 ns的连续光谱弛豫过程,而光谱移动量可作为SNase变体蛋白结构紧密程度的判断依据。飞秒上转换数据分析结果中,0.5 ps的DAS在光谱蓝端为正、红端为负,表明了色氨酸残基受到弛豫效应的影响。200 ps的寿命则说明色氨酸残基与周围猝灭基团之间存在电子转移过程。时间分辨荧光各向异性(anisotropy)的分析结果则说明了色氨酸残基在蛋白质体系内具有独立的局部运动,且其强弱与变体的热稳定性和热运动的整体效果有关。测量和分析色氨酸残基的时间分辨荧光性质为深入研究SNase蛋白的结构和功能提供了新的思路。     

Excitation and Emission Spectra of Cs2NaLnCl6 Crystals Using Synchrotron Radiation

ABSTRACT

The visible emission and vacuum ultraviolet excitation spectra of the series Cs₂NaLnCl₆ (Ln = Y, Nd, Sm, Eu, Tb, Er, Yb) and Cs₂NaYCl₆:Ln³⁺ (Ln = Sm, Er) have been recorded using synchrotron radiation at room temperature, and in some cases at 10 K. The excitation spectra comprise features associated with charge transfer, excitation from the valence to conduction band, and impurity bands. No d–f emissions were observed for these Ln³⁺ ions, so that the emission bands comprise intraconfigurational 4f ^N –4f ^N transitions and impurity bands, whose natures are discussed. Theoretical simulations of the f–d absorption spectra have been included. The comparison with data from the synchrotron at Desy enables a comprehensive account of the ground (or vibrationally excited ground for Ln²⁺) states of the Ln³⁺ 4f ^N , Ln³⁺ 4f ^N?15d, and Ln²⁺ 4f ^N+1 configurations relative to the valence and conduction bands of Cs₂NaLnCl₆, for which the band gaps are between 6.6 and 8.1 eV.     

Luminescence property studies of α-Al2O3 by means of nanosecond time-resolved VUV spectroscopy

The luminescence spectra of corundum monocrystals grown by different methods are investigated by means of a time-resolved spectroscopy method at temperatures 90 K and 300 K. The existence of fast and slow emission in the VUV luminescence spectra of irradiated and nonirradiated crystals was observed. We observed luminescence bands with a maximum at 326 nm produced by F ⁺ centers. A new type of fast luminescence at the band of 270 nm was found. This is known as cross-luminescence and is connected with the recombination of valence band electrons with the holes in the low ground band. It was shown that the band of 410 nm isn't due to to anionic centers (F-centers), but is determined by the short lifetime center of emission (F ^- -centers). Received 20 October 1998 and Received in final form 20 January 1999     

Time-resolved luminescence spectroscopy of pure and doped with Ce3+ ions SrAlF5 crystals

The results of a study of time-resolved photoluminescence (PL) and energy transfer in both pure and doped with Ce³⁺ ions SrAlF₅ (SAF) single crystals are presented. The time-resolved and steady-state PL spectra in the energy range of 1.5–6.0 eV, the PL excitation spectra and the reflectivity in the energy range of 3.7–21 eV, as well as the PL decay kinetics were measured at 8.8 and 295 K. The lattice defects were revealed in the low temperature PL spectra (emission bands at 2.9 and 4.5 eV) in the undoped SAF crystals. The luminescence spectra of the doped Ce³⁺:SAF crystals demonstrate a new selective emission bands in the range of 3.7–4.5 eV with the exponential decay kinetics (τ ≈ 60 ns at X-ray excitation). These bands correspond to the d-f transitions in Ce³⁺ ions, which occupy nonequivalent sites in the crystal lattice.     

Absorption,excitation and fluorescence spectra of thallium activated cesium bromide

Absorption, excitation and fluorescence spectra of T1⁺ doped cesium bromide have been investigated at various thallium concentrations. At very low thallium concentration two absorption bands are obtained at 225 nm and 264 nm. With rise of thallium concentration additional absorption bands are obtained at 230, 244, 258, 270 and 285 nm. A single bell-shaped fluorescence band at 357 nm in the ultraviolet region is obtained at low thallium concentration. Two additional visible fluorescence bands appear at 440 and 540 nm with rise in thallium content. The excitation spectra for ultraviolet emission band and visible emission bands are found to be different. Accordingly the ultraviolet emission band is attributed to the characteristic A emission in T1⁺ ion and the visible bands are attributed to dimer centers havingD _4h site symmetry.     

Diagrammatic representation of the third-order polarization in transient CARS

Summary A diagrammatic perturbative approach is adopted to derive the expression for the third-order polarization,P ⁽³⁾ which originates the anti-Stokes emission in a time-resolved CARS experiment. The various contributions toP ⁽³⁾ are calculated assuming that laser fields are off-resonance with respect to any electronic level of material system. The resonant part of the polarization consists of two terms, in which the roles of the pump and probe pulses at frequency ω₁ are exchanged. The global expression allows the direct calculation of the signal time profile in a transient CARS experiment once a model is assumed for the laser pulse shape.     

单斜结构的Yb:KLu(WO4)2晶体光谱和激光性质的各向异性

研究了Yb:KLu(WO₄)₂晶体对非偏振抽运光的吸收以及连续波激光振荡性质. 晶体结构的低对称性导致晶体光谱呈强烈各向异性,最强的吸收和发射都发生在平行于N_m主轴的偏振方向上. N_g切向晶体具有最高的非偏振抽运光吸收效率和最大的激光功率产生潜力,2 mm长的晶体产生的最高连续波输出功率为11 W,相对于吸收抽运功率,光—光转换效率为68%,而斜率效率则达80%. 关键词： 吸收谱 发射谱 激光振荡 各向异性     

Emission Spectra of BeO in Near Ultraviolet Region

Abstract

The emission spectra of isotopic BeO molecules as excited in low-pressure arc have been photographed in the region 300–350 nm at medium dispersion. The bands have been assigned to the c³II ? a³II system. The vibrational numbering was obtained from a study of the vibrational isotope effect. Vibrational constants for involved states are derived from least-squares fits of the measured bandhead wavenumbers.     

Time-dependent57Fe-species in57Co-labeled cobalt(II) iodate studied by means of coincidence Mössbauer spectroscopy

A lifetime of unstable⁵⁷Fe(II)-species formed through EC-decay of⁵⁷Co-labeled Co(IO₃)₂ was estimated using a coincidence technique. KX-ray-gated and time-resolved emission Mössbauer spectra were measured at room temperature. No remarkable difference was found ont he relative intensity ratio of⁵⁷Fe(II)/⁵⁷Fe(III) between the X-ray-gated and time-integral emission spectra. A mean lifetime of the unstable⁵⁷Fe(II)-species was estimated to be 43±5 ns from the time-resolved emission Mössbauer spectroscopy.     

Investigation of thermoluminescence in Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> phosphors doped with Cu,Ag and Mg

Li2B4O7 (LBO)Cu,Ag,Mg phosphors have been prepared by the sintering technique.The roles of the Ag and Mg dopants in the phosphors have been studied using the methods of thermoluminescence (TL) glow curves and TL 3D spectra. The results indicated that proper concentrations of Ag and Mg can enhance the TL of LBOCu.It was also indicated that the intensity of TL peak at ～130℃ is reduced with the increasing Ag concentration, and enhanced with the increasing Mg concentration.From the TL 3D spectra, three emission bands (λ1 = 421 nm,λ2 = 380 nm, λ3 = 350nm) were observed the intensity of low energy emission band is reduced and that of the high energy is enhanced with the increasing dopant Ag; on the contrary, the intensity of low energy emission band is enhanced and that of the high energy one is reduced with the increasing dopant Mg.     

Study on wave packet dynamics of E~1Σ_g~+ state of Li_2 with femtosecond-resolved photoelectron spectra

Wave packet dynamics of the Li₂ molecule are investigated by using the time-dependent quantum wave packet method, and the time-resolved photoelectron spectra of the Li₂ molecule are calculated. The time-resolved wave packet theory is used to reasonably interpret the phenomena of the photoelectron spectra for different parameters. Our calculation shows that the loss of the wave packets in the shelf state area of E{ }^1\Sigma_g^ + plays a prominent role in the process of photoionization with the increase of the delay time. Moreover, the oscillation of the wave packet on the E{ }^1\Sigma_g^ + curve symbolizes a decreasing process of energy.     

Light scattering spectra of polarization fluctuations and models of the phase transition in KDP type ferroelectrics

Abstract

Recent light scattering studies in KH₂PO₄ type hydrogen-bonded crystals are reviewed. Dynamical properties of these crystals have been discussed in terms of the coupled tunneling proton-optical phonon model up to date. Light scattering spectra in several GHz and cm^?1 regions with various scattering geometries observed in KH₂PO₄, KD₂PO₄ and their mixed crystals, however, revealed that all these spectra are well analysed in terms of a coupled polarization relaxation mode-acoustic phonon system. Since most of the spontaneous polarization is due to shifts of K, P and O ions, relaxation motions of H₂PO₄ dipoles arc concluded to be the origin of these low-frequency spectra. Models of the phase transition mechanism are discussed on the basis of these results and other recent experimental studies including the explanation of large isotope effects in these crystals.     

Comparison Between the IR Spectra and the Structure of the Two Conformations of a Diazabicyclanol

Abstract

In the two stable conformations of the diazabicyclanol 3, 7-dimethyl-3, 7-diazabicyclo[3. 3. 1]nonan-9-ol, chair-chair (Va) and chair-boat (Vb), the infrared spectra (200–4000 cm^?1) were recorded, compared and their vibrations analysed. Using the AMI senlempirical method, the geometry was fully optimized in both forms, and the theoretical Infrared spectra were calculated and compared. In the (Vb) conformation, the IR spectra were recorded in CCl₃D, CCl₄ and S₂C solvents. Some correlations were established.