Ionic Equilibria of Fluorophores in Organized Solutions: The Influence of Micellar Microenvironment on Protolytic and Photophysical Properties of Rhodamine B

Ionic equilibria and fluorescence decay of rhodamine B were studied in micellar solutions of sodium n-dodecyl sulfate (SDS) with various additives (NaCl, pentanol-1, crown ether, and tetra-n-butyl ammonium salt), and five nonionic surfactants (Brij 35, nonyl phenol 12, Triton X-100, Triton X-305, Tween 80), as well as in -cyclodextrin solutions. The apparent dissociation constants, , of rhodamine B (HR⁺ R + H⁺) were obtained. The distribution of the dye species HR⁺ and R in the ultramicroheterogeneous systems was studied using absorption and emission spectra, fluorescence life-times, , and the plots of p versus surfactant concentration. The p values under conditions of complete binding, p , were found to be markedly higher than that in water . The medium effects, , in organized solutions studied are in accord with the charge type of the acid-base couple +/±, confirming the zwitterionic nature of rhodamine B neutral species. Both and a values of the dye were shown to sense the changes in the micellar microenvironments, and the possibility of using rhodamine B as an interfacial acid-base indicator, for example, for monitoring of surface potentials and of bulk ionic strength, were demonstrated.     

The Influences of Structural Evolution of Silica Gel Glass on the Photophysical Properties of Benzoic Acid

Benzoic acid was dispersed into silica gel glass at molecular level by sol-gel process. The luminescence properties of benzoic acid in gel glass heat-treated at various temperatures were studied. The changes in gel glass structure and the surrounding environment of benzoic acid resulted in different electronic transitions, and thus the different luminescence spectra. The fluorescence bands centered at 320 nm and 355 nm, respectively induced by the S_1* S₀ transition of benzoic acid and S_1n* S₀ transition of benzoate anions, respectively, were observed when the doped gel glass was heat-treated at the temperatures below 200°C and at the temperature range 300 400°C, respectively. On heating at 500°C, benzoate anions were steadily immobilized in the cages of the Si–O network with the SiO₄ tetrahedra formation and the RTP of benzoate anions is observed. It is proposed that the luminescence spectra of benzoic acid can be used as a structural evolution probe of gel glass.     

非线性延迟响应对啁啾类孤波的影响

以描述超短光脉冲在光纤中传输的高阶非线性Ginzburg-Landau方程为模型,给出了包含三阶色散,自陡效应以及非线性延迟响应等效应的锁模激光器系统的啁啾类孤波解,并采用分步傅立叶方法对该解析解的稳定性进行了详细的分析。结果表明:在一定的系统参数条件下,即使存在一些微弱的扰动,这类啁啾类孤波解依然可以稳定地存在并传输较长的距离。如果初始输入脉冲为任意的高斯脉冲,在经过一段传输距离的演化后,啁啾类孤波解形成并可以稳定传输。     

Impact of Magnetic Pulses on the Structural State of Surfactant Solutions

The impact weak pulses of a magnetic field have on the structure of micellar aqueous solutions of bromide cetyl- trimethylammonium is determined experimentally via gas-discharged visualization. The type of optoelectronic emission patterns depends on the number of magnetic field pulses and corresponds to different modifications of planes of cubical and hexagonal packing.     

Solvatochromic Effect on the Photophysical Properties of Two Coumarins

The absorption and emission spectra of two coumarins namely 7, 8 benzo-4-azidomethyl coumarin (C₁) and 6-methoxy-4-azidomethyl coumarin (C₂) have been recorded at room temperature in solvents of different polarities. The ground state dipole moments (μ _g ) of two coumarins were determined experimentally by Guggenheim method. The exited state (μ _e ) dipole moments were estimated from Lippert’s, Bakhshievs and Chamma-Viallet’s equations by using the variation of Stoke’s shift with the solvent dielectric constant and refractive index. The ground and excited state dipole moments were calculated by means of solvatochromic shift method and also the excited state dipole moments are determined in combination with ground state dipole moments. It was observed that dipole moments of excited state were higher than those of the ground state, indicating a substantial redistribution of the π-electron densities in a more polar excited state for two coumarins.     

Substitution Effects on the Photophysical Characteristics of the Salicylic Anion

Spectral and photophysical properties of substituted salicylic anions are investigated by steady-state and time-resolved fluorescence spectroscopy for a variety of electron donating substituents at the positions para to the hydroxyl and carboxylic groups. Next to the usual excited-state intramolecular proton transfer in aqueous solution, an excited-state intermolecular proton transfer is found to be responsible for the dual emission observed in the case of 5-aminosalicylic anions.     

Photophysical properties of the Corrole photosensitizers

The photophysical properties of a series of hydroxyl Corroles, Corrole-F, Corrole-Cl, Corrole-Br, Corrole-I and Corrole-2I, have been investigated by steady-state and time-resolved transient spectroscopy. The absorption spectra show a strong peak around 420 nm corresponding to B band and several weak Q absorption bands between 450 nm and 650 nm, exhibiting much stronger Q band absorption than that of porphyrin. The absorptions of these Corroles increase with the atom weight and the number of halogen atoms. All samples show similar fluorescence characteristics of an emission peak at 650 nm. The fluorescence intensities significantly decrease with the atom weight and the number of halogen atoms. The fluorescence quantum yield of Corrole-I is 0.947%, which is larger than that of Corrole-2I (0.381%). The fluorescence dynamics of the hydroxyl Corroles shows that both the fluorescence lifetime and the intersystem-crossing transition time of these Corroles decrease sharply with the increase of the atom weight and the number of halogen atoms, which may lead to the increase of the triplet state quantum yield. The heavy-atom effect on active oxygen of PDT has also been discussed by the end of this paper.     

Molecular Dynamics Study of the Structural Modification of Porous Silica from Low-Energy Recoils

Molecular dynamics simulations are performed to investigate the effects of low-energy recoils on the microscopic structure of porous silica. Exhibiting a logistic growth with the recoil energy, the displacement probability of Si is shown to be smaller than that of O at the same primary knock-on level. Computations of pair distribution functions and bond angle distributions reveal that this material upon irradiation with energies around the displacement thresholds mainly undergoes structural changes in the medium-range order. In the porous network,while the formation of nonbridging oxygen defects tends to induce shorter Si–O bonds than those formed by bridging oxygen atoms, a remarkable increase of inter-tetrahedral bond angles created by multiple recoils can be observed and associated with the rearrangement of ring statistics.     

Structural Modification and Erosion of Plasma-Irradiated Tungsten and Molybdenum Surfaces

Technical Physics - Data for the structural modification and erosion of plasma-irradiated tungsten and molybdenum surfaces are reported. It has been found that the irradiated specimen surface shows...     

Enhanced Exciplex Emission of Pyrene Thin Films Doped by Perylene: Structural,Photophysical and Morphological Investigation

The present work reports on the preparation of thin films of pyrene luminophors doped by varying amounts of perylene by spin coating technique. The structural, morphological, and photophysical properties of pyrene thin films have been investigated as a function of perylene contents. X-ray diffraction studies of doped thin films show well-defined peaks, and estimated crystallite size decreases with increasing perylene content, due to the formation of closed packed crystal structure. SEM images of pure pyrene revealed smooth, and compact and separated crystals with amounts of perylene. The result of absorption spectra showed decrease in intensity with perylene content. However, the fluorescence spectra of pyrene containing higher amounts of perylene showed broad and structureless exciplex emission at 510 nm. The emission colour of pyrene luminophors tuned from blue to green by controlling the concentration of perylene. The phenomenon of change in colour was seen due to efficient excitation energy transfer from pyrene to perylene in thin films. It also found that the intensity of exciplex emission increases with increasing concentration of perylene is of high demand in fluorescent lamp as well as green organic light emitting diodes.     

Photophysical Processes in the Vapor of Carbazole

The characteristics of the rapid and retarded fluorescence of the vapor of carbazole excited by the radiation of a nitrogen laser are studied. The dependences of the intensity and rate of decay of the retarded fluorescence on the exciting-radiation intensity, the temperature, and the pressure of the vapor and foreign gases are used to determine the predominant mechanisms of relaxation of triplet molecules. It is shown that the decay of the retarded luminescence is governed by the competition between the processes of triplet-triplet annihilation that lead to the emission of annihilation retarded fluorescence and intercombination conversion of the triplet molecules to the ground electronic state. The characteristic times of these processes and the lifetimes of the triplet state in the vapor _T are evaluated; the temperature dependence of _T is analyzed in a wide interval of temperatures (77–573 K). It is inferred that in all aggregative states, the reduction in _T with increase in the temperature has a common nature and reflects an increase in the rate of intercombination transition T ₁ — S ₀ with increase in the content of vibrational energy.     

Photophysical study on daunorubicin by fluorescence spectroscopy

Steady-state fluorescence and time-resolved fluorescence intensity decays of daunorubicin have been studied in polar solvents and in aqueous solution by a time-correlated single-photon counting technique. Daunorubicin, quinizarin, and 2,3-dimethylquinizarin show bi-exponential decay. The decay of daunorubicin becomes tri-exponential in the presence of adenosine 5′ monophosphate. The quenching of the fluorescence of daunorubicin by adenosine 5′ monophosphate exhibits downward deviation from the Stern-Volmer linearity, suggesting the existence of fluorophore in two conformers in the ground state differing only in the extent of hydrogen bonding.     

Influence of the Characteristics of Impact Excitation on the Parameters of Electromagnetic Response from Dielectric Materials

The influence of the energy and duration of impact excitation on the parameters of electromagnetic response from structural dielectric materials is investigated. It is established that the first pulse of electromagnetic response is due to the electrization of the material at the impact point, and the pulse duration determines the active impact excitation phase. The transformation of the amplitude-frequency characteristics of the electromagnetic response attendant to changes of the impact excitation parameters is observed, which testifies to the linearity of mechanoelectric transformations for impact excitation energy of the order of 3·10^–2 J.     

高速碰撞过程中应变硬化材料靶动态响应研究

 给出了适用于可压缩、弹塑性、按幂次律应变硬化材料的动态柱形腔膨胀模型和侵彻模型，并编制了相应的计算程序。腔膨胀模型给出靶中应力分布情况，侵彻模型根据腔膨胀模型的有关结果来预估具有锥形头部的刚性弹丸侵彻半无限厚靶的最终侵彻深度以及贯穿薄靶时的弹丸剩余速度和弹道极限速度。给出了钨合金弹丸正碰5083-H131铝靶和钢弹丸正碰6061-T651铝靶的一些计算结果，计算结果与实验结果及二维拉氏弹塑性LTZ-2D程序的数值模拟结果符合得很好。     

Time-Resolved Fluorescence Spectroscopy Study on the Photophysical Behavior of Quantum Dots

Room-temperature time-resolved luminescence measurements on single CdSe/ZnS quantum dots (QDs) are presented. Fluorescence emission spectra were recorded over periods of up to 30 minutes with a time resolution as small as 6 ms. For QDs in ambient air, a clear 30–40 nm blue shift in the emission wavelength is observed, before the luminescence stops after about 2–3 minutes because of photobleaching. In a nitrogen atmosphere, the blue shift is absent while photobleaching occurs after much longer times (i.e., 10–15 minutes). These observations are explained by photoinduced oxidation. The CdSe surface is oxidized during illumination in the presence of oxygen. This effectively results in shrinkage of the CdSe core diameter by almost 1 nm and consequently in a blue shift. The faster fading of the luminescence in air suggests that photoinduced oxidation results in the formation of non-radiative recombination centers at the CdSe/CdSeO_x interface. In a nitrogen atmosphere, photoinduced oxidation is prevented by the absence of oxygen. Additionally, a higher initial light output for CdSe/ZnS QDs in air is observed. This can be explained by a fast reduction of the lifetime of the long-lived defect states of CdSe QDs by oxygen.     

内凹负泊松比蜂窝结构的面内双轴冲击响应

利用有限元模拟方法研究了内凹负泊松比蜂窝结构的面内双轴冲击响应。用节点扰动方法建立了具有不同规则度的内凹负泊松比蜂窝结构,并将其在不同冲击速度下的变形模态、应力-应变曲线和能量耗散能力与规则蜂窝进行了对比分析。结果表明,冲击速度是内凹蜂窝结构变形模态最主要的影响因素。此外,在双轴冲击下,由于不规则度的引入,延长了应力-应变曲线的平台阶段,抑制了结构的各向异性程度,从而使结构的变形特征从局部密实转向整体密实。在能量吸收能力方面,结构的不规则性导致了密实化阶段的滞后,因此在相同的压缩程度下,其塑性耗散能低于规则模型。