聚合物O-PPV的链间相互作用的研究

近年来,聚对苯乙炔(PPV)及其衍生物作为一类性能优良的电致发光材料而受到人们的广泛关注[1].这是因为聚合物发光材料能通过化学裁剪方法来改善发光效率、颜色、成膜性等特性.载流子形成激子以及激子的辐射和非辐射衰减过程向来是聚合物发光二极管(LEDs)发光的重要环节,因此研究聚合物的光物理过程对提高器件的发光特性是非常重要的.     

Time integral and time differential Mössbauer measurements on [57Co/Mn(bipy)3](PF6)2

The Mössbauer emission spectra of nucleogenic iron(II) complexes with a low spin (LS) ground state show two metastable iron(II) high spin (HS) states at low temperatures. In order to identify these metastable HS states, the compound [⁵⁷Co/Mn(bipyridine)₃](PF₆)₂ has been studied by time differential Mössbauer emission spectroscopy (TDMES) and optical lifetime measurements of excited electronic states in the corresponding Fe-doped Mn compound. The lifetime of one of the HS states of the nucleogenic iron(II) determined by TDMES has been measured to be the same as the lifetime of the laser-excited iron(II) electronic state.     

Luminescence spectra of Mn(II) in different symmetries

Luminescence emission and excitation spectra of high-spin Mn(II) were studied in crystals with different site symmetries of the divalent ion. For cubic or uniaxial site symmtries only one emission band is observed with a maximum asymmetry of 20% and larger width on the low energy side. Lower site symmetries may result in spectra of considerable complexity. A second emission band of lower intensity near 14 000 cm^-1 was found in systems with hexa- as well as tetra-coordinated Mn(II). It evidently originates from the same Mn(II) that gives rise to the stronger emissions at higher energies. A qualitative explanation for its occurence on the basis of close-lying split components of the ⁴T₁(G) or ⁴T₂(G) states is presented. In two systems emission bands from higher excited states and shifts of emission maxima with excitation energy were observed. The shifts are explained on the basis of overlapping bands and variable intensity ratios for these unresolved components. The results indicate that the degree of distortion is more important for the occurrence of these complications than the actual site symmetry of Mn(II).     

Photophysical parameters and laser performance of 3-(4′-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one (DMAFP): A new laser dye

The spectral properties such as singlet absorption, molar absorptivity, emission spectra, fluorescence quantum yield and excited state lifetime of 3-(4′-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one (DMAFP) have been determined in different solvents. DMAFP dye exhibits a large red shift in both electronic absorption and emission spectra as the solvent polarity increases, indicating a large change in the dipole moment of molecules upon excitation. A crystalline solid of DMAFP gives an excimer like emission at 566 nm due to the excitation of molecular aggregates. This is expected from the idealized crystal structure of the dye that belongs to the B-type class of Steven's classification. The ground and excited state protonation constants of DMAFP are calculated and amounted to 1.71 and 8.3, respectively. DMAFP acts as a good laser dye upon pumping with nitrogen laser (λ_ex=337.1 nm) in chloroform, methylene chloride and dioxane and gives laser emission in the range 460–590 nm. The laser parameters such as the tuning range, gain coefficient (α), emission cross section (σ_e) and half-life energy (E_1/2) are calculated. The photoreactivity and net photochemical quantum yield of DMAFP in chloromethane solvents are also studied.     

GaAs中Cr2+离子的发光及杨—泰勒效应

在各向同性压力下,观察到77°K时n—GaAs样品中Cr2+离子的光致发光。这个光谱带是由Cr2+离子的激发态5E到基态5T2的跃迁所致。由于Cr2+离子在晶体场中有较强的杨一泰勒效应,时发光光谱产生影响。本文考虑静态杨一泰勒效应计算了发射光潴,估计了杨一泰勒能量,并与实验结果相比较。     

The Rotational Analysis of the A(2)Pi(r)-X(2)Sigma(+) Band System of MgBr

The A(2)Pi(r)-X(2)Sigma(+) emission spectrum of the magnesium monobromide radical, MgBr, has been recorded with a Fourier transform spectrometer modified to record double-sided interferograms. The emission spectra of the Deltav = -2, -1, 0, +1 bands were generated in a microwave discharge of a mixture of argon and vaporized MgBr(2). The Deltav = 0 and -1 bands were rotationally resolved, but the F(2) spin component (A(2)Pi(3/2)) in the (1, 1), (1, 2) and vibrational bands with v' > 1 were missing in our spectra because of a strong predissociation in the A state. The molecular constants in both electronic states were determined for the two bromine isotopomers. The r(0) bond length in the A state is about 2.327 ?, which is about 0.02 ? shorter than in the ground state. Franck-Condon factors were calculated from the Rydberg-Klein-Rees potentials, and they reproduce the observed relative intensities of the bandheads. An upper limit for the dissociation energy (D(0)(0)) was obtained as 26 268.4 cm(-1), based on the absence of the energy level with v = 1, A(2)Pi(3/2), J = 1.5 in our spectrum. Copyright 2000 Academic Press.     

Analysis of high temperature ammonia spectra from 780 to 2100 cm

A recently-recorded set [Hargreaves et al., Astrophys. J., in press] of Fourier transform emission spectra of hot ammonia is analyzed using a variational line list. Approximately 3350 lines are newly assigned to mainly hot bands from vibrational states as high as v₂ = 2. 431 new energy levels of these states are experimentally determined, considerably extending the range of known rotationally-excited states. Comparisons with a recent study of high J levels in the ground and first vibrational states [Yu et al., J. Chem. Phys., 133 (2010) 174317] suggests that while the line assignments presented in that work are correct, their energy level predictions suffer from problems associated with the use of very high-order perturbation series in the effective Hamiltonian. It is suggested that variational calculations provide a more stable method for analyzing spectra involving highly-excited states of ammonia.     

Potential curves from continuous spectra: He2 X 1Σ g + and A 1Σ u +

Continuous electronic spectra of diatomic molecules can often be related to the associated potential curves. It is demonstrated that the local nature of continuous spectra may greatly facilitate inversion of the spectra to obtain ground and excited state potential curves. All of the observed continuous spectra related to transitions between the X and A states of the helium diatomic molecule are re-examined with the goal of determining accurate potential curves for the two states. It is shown that the excited state dissociation energy is 2·50±0·03 eV and that the MDD-1 potential proposed by Bruch and McGee is the preferred choice to represent the ground state interaction. Also, the mean cross section at 300 K for the destruction of a 2¹ S helium atom by collision-induced emission is evaluated and found to be 2·8 × 10^-20 cm² in agreement with the measurements of Phelps.     

Angle resolved UV photoemission spectra from a Bi(0001) surface

Angle resolved photoemission spectra taken from a Bi(0001) surface for hv = 16.9 and 21.2 eV exhibit (1) broad features which appear to be associated with one dimensional density of states, rather than band like features, and (2) a weak dependence upon the direction of incident light These effects can be explained by a large number of nondegenerate final state bands available for optical emission and by a uniform mixing of atomic orbitals in the initial states.     

An angle-resolved photoemission study of the chemisorption of chalcogens on Cu(100): II. Cu(100) + c(2 × 2)O

Starting with the three-step direct-transition model of ARPES for bulk materials, which was examined in the preceding paper, we propose a framework for describing changes in the photoemission spectra due to chemisorption. Normal emission ARPES data for Cu(100) with a c(2 × 2)O overlayer were obtained in the photon energy range hv = 11 to 34 eV. These spectra have been compared within the proposed framework with those obtained from clean Cu(100). Changes were found in the Cu emission features which could be explained by the relaxation of momentum conservation perpendicular to the surface in the optical excitation step and by the relaxation of momentum conservation parallel to the surface in the escape step. These changes include a photon energy dependent broadening of the d-band peak and the preferential attenuation of the sharp direct-transition feature associated with the sp-band. Some evidence for a surface resonance at the top of the d-bands has been obtained. Changes in the spectrum of scattered electrons were related to modifications of evanescent final states. A 1.3 eV wide band derived from the oxygen p_x,y-orbitals was deduced from spectra obtained at normal emission and along the $\text{Γ}\text{X}$ and $\text{Γ}\text{M}$ lines of the surface Brillouin zone. On the other hand, no emission was clearly detected from the oxygen p_z-orbitals. Oxygen induced emission above the Cu d-bands was observed and attributed to antibonding states. This emission was directed towards the bulk [011] directions.     

Role of aggregation in the amplified spontaneous emission of [2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] in solution and films

The amplified spontaneous emission (ASE) spectra of the conjugated polymer [2-methoxy-5-(2′- ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is investigated under different conditions such as thin film and solution, solvent type and concentration. Results indicate that aggregation has a pronounced effect on ASE spectra. In solution form, as concentration was increased and thus the proportion of aggregates, a decrease in the ASE emission bandwidth and a red shift of the ASE peak was observed. For the thin film samples, the ASE spectra show two emission bands which were assigned to the first and second vibronic transition of the polymer chains.     

Photophysical characterization of pyrazino[2,3-c]-1,2,6-thiadiazine 2,2-dioxides in DMSO and acetonitrile solutions

Photophysical characterization of some pyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxides derivatives in DMSO and acetonitrile has been carried out. Acid-base processes have been found to occur in the ground and excited states. In DMSO and acetonitrile equilibrium between the neutral and deprotonated molecules is established in the ground state. In acetonitrile, a second equilibrium between the neutral and protonated form is also present at a lower pH, and can be treated independently of the first one. Absorption, emission, and excitation spectra of the species involved have been measured; data analysis allows us to calculate pK _aand quantum efficiencies. The change of the decay lifetimes with pH, along with steady state fluorescence measurements show the existence of communication between the excited states and enable us to estimate the excited state kinetic rate constants.A discussion about their possible use as laser dyes based on the energy threshold condition is also given.     

Solvatochromic and Preferential Solvation Studies on Schiff Base 1,4-Bis(((2-Methylthio)Phenylimino)Methyl) Benzene in Binary Liquid Mixtures

The solvatochromic behavior of the 1,4-bis(((2-methylthio) phenylimino)methyl) benzene [BMTPMB] in single solvents and binary mixtures were investigated. Fluorescence spectra show the dual emission due to twisted intramolecular charge transfer (TICT) state. The preferential solvation parameters: local mole fraction, X₂^L, solvation index δ_s2, exchange constant K₁₂ were calculated for the binary mixtures, ACN+MEOH, DMSO+CCl₄ and CCl₄+1,2 DCE. The dipole moment ratios between ground and excited states were deduced using the solvatochromic shifts of absorption and fluorescence spectra as a function of dielectric constant (ε), refractive index (n) and it was found to be 1.25.     

Spin-crossover behavior in a new series of iron (II) compounds based on the ligand 5-(2-pyridyl)-1,2,4-triazole

The title ligand (hereafter LL), is found to form an exciting new series of pseudo-octahedral Fe(II) compounds with formula Fe(LL)₃X₂. N Solvent, which exhibit conveniently studied spin-crossover transformations between nominal⁵T and¹A states of Fe(II). Mössbauer spectra indicate that the spin-crossover transformations for these new systems are probably of the continuous type. There is considerable variation in the degree of conversion to low spin with decreasing temperature depending on gegen ion, solvation and/or location of methyl substituent on the triazole - ligand. The Mössbauer spectra for particular complexes in this group show an absence of both noticeable hysteresis and mechanical grinding effects.     

不同取代基对喹啉电子光谱影响的理论研究

不同取代基团会引起电子光谱发生不同的变化,为获得分子结构与电子光谱之间的关系,采用量子化学计算方法进行了理论分析。使用DFT、CIS分别对基态、激发态进行几何结构优化,再用TDDFT计算优化结果得出电子光谱。结果表明:不同取代基团都改变了碳氮环基态、激发态的几何构型,前线区域轨道能量,π电子共轭系统,这些变化都导致电子光谱发生相应变化。得出不同取代基对电子光谱的影响规律,为电子光谱分析鉴定衍生物提供了理论参考。     

新型锌离子荧光探针(5-(二甲基氨基)-N-(4-(2-(2-喹啉亚甲基)甲酰肼基)苯基)萘-1-磺酰胺)的研究

以丹磺酰胺为荧光基团设计合成了新型Zn²⁺荧光探针DW1(5-(二甲基氨基)-N-(4-(2-(2-喹啉亚甲基)甲酰肼基)苯基)萘-1-磺酰胺)。通过紫外光谱、荧光光谱及电喷雾质谱研究了DW1对Zn²⁺的选择性识别作用。结果表明,DW1与Zn²⁺结合后荧光显著增强,荧光发射光谱由545 nm蓝移至515 nm,量子产率达到0.32,且对Zn²⁺具有较高的选择性,受常见离子的干扰较小。光谱滴定和ESI-MS谱表明DW1与Zn²⁺以1∶1的化学计量数形成配合物,平衡常数K=1.75×10⁴(mol/L)^-1。     

水杨醛缩对乙酰基苯胺希夫碱的合成及其荧光性质的理论研究

以水杨醛和对乙酰基苯胺为原料,首次采用绿色环保的室温固相反应方法制备了水杨醛缩对乙酰基苯胺希夫碱,用元素分析和核磁共振氢谱对产物进行了表征。测定了产物的紫外光谱、荧光光谱和相对荧光量子效率,发现该化合物具有较强的荧光性质。利用密度泛函理论(density functional theory, DFT)方法,在B3LYP/6-311G基组水平上优化了该化合物的基态分子构型。采用相同的方法和基组计算了标题化合物的振动频率,频率数据中没有虚频,即该优化构型是稳定的。分析理论计算结果发现：标题分子具有较强的芳香性和较大共轭体系。在基态优化结构的基础上应用含时密度泛函理论(TD-DFT),在B3LYP/6-31G水平上计算并研究了此化合物的吸收光谱。用单激发组态相互作用(CIS)方法优化了标题分子的激发态构型,并在此基础上用TD-DFT//B3LYP/6-31G方法计算了这种化合物的荧光发射光谱。将理论计算的光谱性质与实验的光谱数据相比较发现二者吻合较好。分析探讨了化合物分子的结构与其荧光性质之间的关系,为进一步寻找具有荧光性质的化合物提供了理论指导。     

Measurements and predictions of hooded crow (Corvus corone cornix) call propagation over open field habitats

In a study of hooded crow communication over open fields an excellent correspondence is found between the attenuation spectra predicted by a "turbulence-modified ground effect plus atmospheric absorption" model, and crow call attenuation data. Sound propagation predictions and background noise measurements are used to predict an optimal frequency range for communication ("sound communication window") from an average of crow call spectra predicted for every possible combination of the sender/receiver separations 300, 600, 900, and 1200 m and heights 3,6,9 m thereby creating a matrix assumed relevant to crow interterritorial communication. These predictions indicate an optimal frequency range for sound communication between 500 Hz and 2 kHz. Since this corresponds to the frequency range in which crow calls have their main energy and crow hearing in noise is particularly sensitive, it suggests a specific adaptation to the ground effect. Sound propagation predictions, together with background noise measurements and hearing data, are used to estimate the radius of the hooded crow active space. This is found to be roughly 1 km in moderately windy conditions. It is concluded that the propagation modeling of the sort introduced here could be used for assessing the impact of human noise on animal communication.     

Spectral behavior study of 3-(4-dimethylamino-phenyl)-1-{6-[3-(4-dimethylamino-phenyl)-acryloyl]-pyridin-2-yl}-propanone

The photophysical properties such as singlet absorption, molar absorptivity, fluorescence spectra, fluorescence quantum yield (?_f) and transition dipole moment (μ₁₂) of 3-(4-dimethylamino-phenyl)-1-{6-[3-(4-dimethylamino-phenyl)-acryloyl]-pyridin-2-yl}-propanone (DMAPAPP) have been studied in different media. DMAPAPP exhibits a large red-shift in both absorption and emission spectra as the solvent polarity increases, indicating a large change in dipole moment of molecule upon excitation. The fluorescence quantum yield depends on the nature of the solvent. The absorption and emission spectra of DMAPAPP in dioxane–water mixture are also studied. The effect of different type of surfactants to determine their critical micellar concentration (CMC) and the microemulsion effect on the electronic absorption and emission spectra of DMAPAPP are recorded. The effect of acidity on the electronic absorption and emission spectra of DMAPAPP is studied to determine the pK_a and pK_a^? values.     

Electronic structure of Si(111) surfaces

We report on new angle-resolved photoemission studies of Si(111) 2 × 1 and 7 × 7 surfaces. The emission from the 2 × 1 surface shows much structure. For normal emission the energy positions are insensitive to the photon energy in the range 19–27 eV. The emission has been interpreted as a probe of the surface density of states, SDOS, including both surface states, resonances and bulk-like states. The SDOS was also calculated as a function of parallel momentum k_∥ for a model of the Si(111) 2 × 1 surface obtained from energy minimization considerations. We identify emission from the dangling bond band, which has a positive dispersion of 0.6 eV, and also emission from surface resonances which have some character of the compressed and stretched back bonds. There are also other predicted surface resonances that correspond to experimental peaks which have not been identified in previous work. Except for the dangling bond band, the surface resonances are limited in k_∥ space, so that it is not possible to follow these resonance bands over all angles. Maximum intensity for the normal emission from the dangling bond is obtained at 23 eV, while the emission from the lowest s-like states monotonically increases towards 30 eV photon energy. When annealing the cleaved 2 × 1 surface to the 7 × 7 reconstructed surface, the spectra broaden significantly. The intensity of the dangling bond decreases and we see a very small metallic edge.