“Additional” Absorption Spectrum at Low Temperature in Monocrystalline Anthracene

Low temperature absorption spectra of anthracene monocrystals 1 to 2 mm thick show a set of narrow lines below the first singlet band of anthracene. By comparison with the emission spectra observed by other authors, we associate these lines with the energy levels of chemical or physical traps. We find there are 9 distinct traps each with a vibrational structure formed either by lattice modes only, or by lattice modes combined with vibrational frequencies of anthracene.     

Migration and Annihilation of Triplet Excitation Energy in the Charge-Transfer Anthracene-Tetrachlorophtalic Anhydride Crystal

Abstract

The emission spectra of the charge-transfer crystal of anthracene-tetrachlorophtalic anhydride were studied in the 1.7-300 K temperature range. Delayed fluorescence was observed over the whole temperature range. At temperatures below ～40 K it results from heterogenous (mobile exciton-trapped exciton) triplet-triplet annihilation. At higher temperatures it is due to homogenous triplet-triaplet annihilation. The existence of mobile excitons is also proved by the character of the ESR lines which are very narrow Lorentzians. The phosphorescence, observed only in the range 1.7–40 K, originates from at least two different kinds of traps with energies ～6 cm^?1 and ～140 cm^?1, respectively. The vibrational structure of the phosphorescence is identical to that of anthracene, with 0—0 band blue-shifted by ～400cm^?1. A kinetic model of trapping and detrapping of triplet excitons as well as the nature of the traps are discussed.     

Infrared Spectra and Photoinduced Absorption of C60 Doped Polyhexylthiophene

Abstract

We report the IR spectra and the photoinduced absorption of polyhexylthiophene(PHT) doped with C₆₀. The presence of C₆₀ ^?n anions is observed in the IR spectra by a mode at 1383 cm^?1 and a broad electronic transition at 1.2 eV, while most of the C₆₀ molecules stay neutral. This is indicative that for a small fraction of C₆₀ molecules, charge transfer occurs in the ground state.

The photoinduced absorption spectra display a sharp transition at 1.15 eV peculiar to C₆₀ monoanion, the spectral features change with fullerene concentration. The intensity of the polymer photoinduced bands increases 5-10 times due to photoinduced charge transfer to C₆₀.     

Molecular Vibration Analysis of lonicity and Phase Transition in TMPD-TCNQ (1:1) Charge Transfer Salt

The infrared spectra of the (1:1) charge transfer salt of N, N, N′, N ‘-tetramethyl-p-phenylendiamine (TMPD) with 7, 7, 8, 8-tetracyanoquinodimethane (TCNQ) and with fully deuterated TCNQ are reported. The assignment of the vibrational data is obtained on the basis of the comparison with that of neutral and ionized parent molecules; additional relevant information is extracted from the low temperature (～15 K) infrared and Raman spectra. The vibrational analysis leads one to estimate for TMPD-TCNQ a degree of ionicity of 0.9₂, which corresponds to an almost fully ionic ground state. The interpretation of the vibrational data has been carried out in the light of an appropriate model for the electron-molecular vibration interaction in regular or dimerized mixed stack charge transfer complexes. The study of the temperature dependence of the infrared spectra of TMPD-TCNQ confirms that the already known phase transition at about 220 K is likely associated with a transition from a regular to a dimerized mixed stack.     

Radiation-Induced Radicals in Anthracene Single Crystals

EPR and optical absorption studies have been made on anthracene single crystals irradiated with electrons at liquid nitrogen temperature. Studies of annealing of the EPR spectra induced by irradiation at liquid nitrogen temperature revealed that they consisted of a broad singlet and two sets angular dependent lines. The angular dependence of the latter was studied and they were ascribed to the 9- and 1-dibenzo-cyclohexadienyl radicals. From comparison of the change in the EPR spectra with the change in the optical absorption spectra at room temperature, optical absorption bands at 535 and 675 nm were ascribed to 9- and 1-dibenzo-cyclohexadienyl radicals. An optical absorption band at 645 nm, which is created by irradiation at liquid nitrogen temperature and decays within two hours at room temperature was suggested to arise from the 2-dibenzo-cyclohexadienyl radical. The broad singlet, which is annealed below room temperature, was ascribed to the 9-anthracyl radical.     

Effects of Acceptor Modification on Charge Transfer in Crystals of Donor-Acceptor Systems of TTF

The degree of charge transfer has been determined in six TTF-fluorene derivative charge transfer complexes, using IR and Raman vibrational spectroscopies. It has been found that changes of the intermolecular electronic distribution is strongly influenced by the presence of the dicyanomethylene group, by the increase of the nitro groups, as well as by the symmetry of the acceptor.     

Optical absorption in an equimolar barium borosilicate glass containing titanium ions

Optical absorption spectra were studied in the visible range, between 350 and 3500 nm, in an equimolar barium borosilicate glass containing 0–12 mol% titanium ions. The valence concentration ratio defined as the ratio of the concentration of the lower valence state transition metal ion Ti³⁺, to the total concentration of the transition metal ion Ti³⁺ + Ti⁴⁺, was varied between 0.15 and 0.85 at each concentration. Below a composition of 4% ions, the absorption is attributed to an electron transition between the levels formed by splitting the ²D ground state term of Ti³⁺ in a tetragonally distorted octahedral ligand field as suggested by previous investigators. However, at and above 4%, the contribution of the low-energy tail of the charge transfer band intruding into the visible range has to be considered to explain the results. The charge transfer mechanism involves the interaction transition between Ti³⁺ and Ti⁴⁺ ions.     

Optical properties and valence change of samarium ions in a sol–gel Al2O3–B2O3–SiO2 glass by femtosecond laser irradiation

10Al₂O₃–5B₂O₃–85SiO₂–xSm₂O₃ glasses were prepared by the sol–gel method. The emission spectra of the glasses indicate that the quench concentration of the Sm³⁺ ions is about 0.2 mol%. The emission spectra of the glasses after high-temperature treatment with H₂ gas exhibit the coexistence of the Sm³⁺ and Sm²⁺ ions. We observed the strong emission line of the Sm²⁺ ions and the emission band of the non-bridging oxygen hole center when the glasses were exposed to a femtosecond laser. It indicates that some Sm³⁺ ions were reduced to Sm²⁺ ions by femtosecond laser pulses and non-bridging oxygen hole centers were formed. The ⁵D₀–⁷F₀ emission line of the Sm²⁺ ions by femtosecond laser irradiation shows a red shift, compared with the emission of the Sm²⁺ ions by reduction with H₂ gas. The strong absorption band and weak, sharp absorption lines in the range from the UV to IR come from charge transfer and the transition from the ⁶H_5/2 state to the various excited states of the Sm³⁺ ions. The reduction mechanism of Sm³⁺ ions is discussed.     

EDA complex stability constants and formation enthalpies in a binary liquid crystalline system with induced smectic phase

In the binary system 4,4′-bis-[n-butylamino]-biphenyl/-(2,2-dicyano-ethenyl)-phenyl 4-n-nonyloxybenzoate which due to EDA complex formation exhibits an induced S_A phase, measurements of the charge transfer band, the molar volumina and transition enthalpies were done. By the concentration and temperature dependence, resp., of the charge transfer absorption and the strongly negative excess volumina we estimated the stability constant and the formation enthalpy of the complex. The data obtained by the two independent methods agree sufficiently.     

Assignment of the Lowest Singlet and Triplet States of the Monoaldehyde of Durene

Abstract

The monoaldehyde of durene has been synthesized. It has been shown to be the impurity frequently encountered in spectral studies involving durene crystals. Both the polarized absorption and emission spectra of the protonated and deuterated aldehyde in crystals of durene^h-14 and durene^d-14 have been obtained. Although the lowest excited singlet and triplet states, separated by 2200 cm^?1, are shown to be nπ* a number of features in the phosphorescence spectrum are more characteristic of a ³π* state. The polarization of the absorption spectrum, in particular the 0-0 band and bands involving the excitation of totally symmetric vibrations, is inconsistent with the nπ* nature of the transition. A number of explanations is proposed.     

Charge Transfer in analogous of TCNQ derived from fluorene with TTF

In a series of three TTF-derived dicyanofluorene charge transfer complexes, an increase of the intermolecular charge transfer has been observed for both addition of nitro groups and a suitable symmetry of the fluorene skeleton. A numerical calculus of the charge transfer was based on IR spectroscopy data with respect to the stretching absorption band of the nitrile group.     

Infrared dispersion of liquid 1-propanol

The spectra of the real and imaginary components of the complex refractive index were determined for liquid n-propanol using a new method, which takes into account the dispersion of the refractive index in the visible range and requires integration over the entire absorption range in the near infrared, mid infrared and far infrared spectral regions. From these data the spectra of both components of the complex electric permittivity and complex polarizability of liquid n-propanol were determined in broad optical range (25 000–350 cm⁻¹). Related high-frequency dielectric properties of the liquid were determined and discussed. The total molar polarization was also determined. The molar vibrational polarization related to various spectral ranges has been determined. It has been found to be extremely small for overtone bands. The main contribution stems from the deformation modes of the molecule and from the vibrations of the hydrogen-bonded OH group. The total molar vibrational polarization originating from internal vibrational modes in the 12 000–350 cm⁻¹ region amounts to 2.45 cm³ mol⁻¹, contributing ca. 12.2% to the distortion polarization and 3.8% to the total molar polarization.     

A molecular dynamics study on vibration spectra of a-SiO2 surface

The charge equilibration (QEq) method was used in the molecular dynamics study of the vibration spectra on the a-SiO₂ surface. The vibrational density of states (VDOS) of a silica glass surface and partial contribution of Si and O atoms were compared with those obtained from the fixed-charge (FQ) model. The VDOS in each of the samples has two groups of vibrational bands, i.e., wide-lower-frequency band (WB) between 0-25 THz and narrow-higher-frequency band (NB) between 25 and 40 THz, which is similar to the bulk VDOS obtained experimentally. The QEq surface exhibits a peak and two shoulders while two peaks are found for the FQ surface. At the surface, an excess peak (at 1-2 THz) was observed by substracting the Debye VDOS from the calculated VDOS, which is regarded as the experimentally observed the boson peak (BP). The position of the BP is shorter than that in the case of the bulk. In the FQ surface, the VDOS consists of narrower bands, while in the QEq sample, wider bands exist due to charge variation.     

Optical properties of pure and metal ions doped ammonium sulfate single crystals

A study of the optical properties of pure‐and some metal ions doped ammonium sulfate crystals (AS) were made. Optical constants of AS crystals were calculated at room temperature. The optical absorption coefficient (α ) was analyzed and interpreted to be in the allowed direct transition. The introduction of Rb⁺ or Cs⁺ ions gives rise to an intense charge transfer band with a maximum at λ= 310 nm in the optical spectrum. In case of Cr³⁺ ‐doping, the absorption shows a shoulder just before the onset band to band transition. The values of the allowed direct energy gap E_g for undoped and doped crystals were calculated. It was found that E_g values were decreased with metal ions doping. The refractive index, the extinction coefficient and both the real and imaginary parts of the dielectric permittivity were calculated as a function of photon energy. The validity of Cauchy‐Sellimeier equation was checked in the wavelength range 4.9 ‐ 5.6 eV and its parameters were calculated. Applying the Single‐Effective‐Oscillator model, the moments of ε (E ) could be estimated. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Superconductivity in (TMTSF)2Clo4 at Zero Pressure

The organic charge transfer salt di-tetramethyl-tetraselenafulvalenium perchlorate becomes superconducting with transition temperatures from 0.9-1.4 kelvin. We compare our results to those of other groups and discuss possible reasons for the observed differences. Preliminary results are given for an alloy with the corresponding perrhenate.     

X-ray diffraction measurements for liquid As2Se3 up to the semiconductor-metal transition region

X-ray diffraction measurements were performed for liquid (1-) As₂Se₃ at temperatures and pressures up to 1500°C and 70 bar. A high-pressure vessel and a sapphire sample cell were developed, according to the authors' own design, for measurements using the energy-dispersive method. The structure factor becomes broadened with increasing temperature and changes significantly at about 1000°C accompanied by the semiconductor-to-metal (SC-M) transition; the first sharp diffraction peak around 1.2Å⁻¹ disappears and the second and third maxima merge. The nearest-neighbor distance and the average coordination number start to increase when the SC-M transition occurs. The density of 1-As₂Se₃ in the temperature and pressure range up to 1600°C and 700 bar, respectively, were also measured by the X-ray absorption method. A volume contraction occurs in the SC-M transition region.     

添加剂对DMH体系电沉积金的影响

在以5,5'-二甲基已内酰脲(DMH)为配位剂的镀液体系中研究了添加剂 C4H6O2、C7H4NNaO3S 和 C12H25 SO4 Na对金电沉积工艺和电结晶过程的影响。阴极极化曲线测试中,金电沉积的最佳电势区间是-0.60~-1.2 V,添加剂浓度在研究的范围内对阴极极化电势的影响较小。循环伏安曲线结果表明,反应界面上添加剂的吸附能够影响成核生长超电势,对金还原过程表现出抑制作用。电化学阻抗谱研究表明,镀液中加入添加剂后,电荷转移过程变得更加困难。 SEM观察表明,添加剂改善了镀层质量,晶粒变得细致、均匀。 XRD分析证实,两种镀液体系中获得的镀金层都沿着Au(111)和(220)晶面择优生长。     

Theoretical and experimental studies on optically tunable hydrogen bonded liquid crystal complex derived from mesogenic and non-mesogenic aromatic compound

A novel hydrogen bonded liquid crystal (HBLC) complex is synthesized from non-mesogenic benzylmalonic acid (BMA) and mesogenic 4-nonyloxybenzoic acid (9OBA). Structural properties and optimized vibrational frequencies of BMA + 9OBA have been studied by FT-IR spectrum. The weak intermolecular interaction between the molecules is proved by NBO and Mulliken charge distribution analysis. The optical and thermal properties are investigated by POM, DSC, UV-Visible and PL techniques. The present HBLC complex exhibits schlieren textures of nematic, broken focal conic texture of smectic C and multicolored mosaic texture of smectic G phases respectively which is not observed in the pure mesogen (9OBA). The HBLC complex geometry is optimized by DFT method at the level of B3LYP basis set 6311G (d, p). The electronic properties of HBLC complex such as, NBO, HOMO-LUMO, ESP and Mulliken charge distribution are also studied. A noteworthy observation is brought out by identifying the presence of photoluminescence in nematic phase due to the variation in intermolecular interaction of the mesophase. The utility of the same complex is discussed. The phase width, thermal stability factor, tilt angle, phase transition temperature and its enthalpy values are reported.     

Synthesis and characterization of potassium, rubidium, and cesium thiogermanate glasses

Glass-forming regions were investigated for the binary xM₂S + (1 − x)GeS₂ (M=K, Rb, Cs) systems. Glasses were prepared from 0?x?0.20 mole fraction alkali sulfide using a novel preparation route involving the decomposition of the alkali hydrosulfides in situ. At higher alkali concentrations near x=0.33, the glass-forming regions are limited by the readily formed adamantane-like M₄Ge₄S₁₀ crystals. Structural characterization of the glasses and polycrystals for x?0.33 were performed using Raman scattering and IR absorption. Terminal Ge-S⁻ vibrational modes, observed between 473 and 479 cm⁻¹, increased in intensity and decreased in frequency with increasing alkali modifier content. Glass transition temperatures decreased with increasing alkali modifier, ranging from 250 to 215 °C. Corresponding crystallization onset temperatures were between 340 and 385 °C. DC conductivity values of the glasses ranged from 10⁻¹⁰ to 10⁻⁷ (Ω cm)⁻¹ with activation energies between 0.54 and 0.93 eV for the temperature range of ∼100-250 °C. Higher ionic conductivities were observed with increasing alkali concentration and decreasing alkali radii. Additionally, an increase in the activation energy was observed above the glass transition temperature.     

The Role of Polymer Cations in The Polymerization and Electrical Conductivity of Polycarbazole

Abstract

The high electrical conductivities (lohm^?1cm^?1) in 3,3’ polycarbazole charge transfer complexes originate from hopping of radical cations delocalized over only two carbazole units. Although some intramolecular transport must occur a significant intermolecular hopping component must be present. In fact there is significant evidence from model compound studies that distinct bound states exist between radical cations on adjacent chains. The radical cations in the N-methyl substituted polymers are so stable that the conductivity remains unchanged for months in air. These same radical cations can propagate a polymerization reaction through exposed chain ends in molten iodine or bromine solvents. Polymerizations, charge transfer doping, solvent casting thus can be carried out by simply dissolving monomer in the molten halogen. The polymerizing liquid iodine solutions can be reduced by S₂O⁴,⁼ to produce neutral polymer.