Spectral broadening and kinetic properties of a Dapoxyl fluorescent probe

The steady-state spectra of Dapoxyl in polar solutions under selective excitation demonstrate considerable spectral inhomogeneity (about 600 cm^?1) in the case of a high viscosity solution. The time characteristics of the luminescence decay in different spectral regions and a long-wavelength shift of the instantaneous emission spectra indicate the occurrence of relaxation processes leading to a decrease in the excited-state energy. A correlation between the luminescence spectra and the processes of intermolecular orientational relaxation of the solution is established.     

Polarization in organic molecular crystals and charge-transfer salts

Polarization in insulators is a general phenomenon that extends over nanometer distances. Two special cases illustrate recent theoretical progress. Polarization energies of localized charges in organic molecular crystals exceed the bandwidth and redistribute the charge density. A systematic treatment of electronic polarization is summarized in the limit of zero intermolecular overlap for pentacene crystals or thin films on metallic substrates, with special attention to the transport gap for producing a separated electron–hole pair and the optical dielectric tensor of the crystal. When overlap cannot be neglected, the general formulation of polarization in extended insulators is in terms of the exact ground state's phase. This formulation is applied to organic charge-transfer (CT) salts whose correlated electronic structure is described by one-dimensional Peierls–Hubbard models. Near the Peierls instability, coupling to lattice modes generates large peaks in the dielectric response that is primarily due to lattice vibrations. Comparisons with experiment are mentioned for both organic molecular crystals and CT salts.     

Spectral luminescent properties of monomeric and associated molecular forms of acridine dyes in polymer matrices

M. V. Lomonosov Moscow State University, Leninskie Gory, 119899, Moscow, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 2, pp. 38–46, March–April, 1995.     

Spectral properties of superfluorescent pulses

We present a spectral analysis of the early stage of superfluorescent pulses. For systems with a Fresnel number near unity and a length long compared to the wavelength of the emitted radiation we find no perceptible frequency shifts or chips.     

Spectral properties of chimera states

Chimera states are particular trajectories in systems of phase oscillators with nonlocal coupling that display a spatiotemporal pattern of coherent and incoherent motion. We present here a detailed analysis of the spectral properties for such trajectories. First, we study numerically their Lyapunov spectrum and its behavior for an increasing number of oscillators. The spectra demonstrate the hyperchaotic nature of the chimera states and show a correspondence of the Lyapunov dimension with the number of incoherent oscillators. Then, we pass to the thermodynamic limit equation and present an analytic approach to the spectrum of a corresponding linearized evolution operator. We show that, in this setting, the chimera state is neutrally stable and that the continuous spectrum coincides with the limit of the hyperchaotic Lyapunov spectrum obtained for the finite size systems.     

Spectral inhomogeneity and wavelength-dependent rotation of probe molecules in membranes

Using subnanosecond laser spectrofluorometry, the spectral and polarization time-resolved characteristics of 1-phenylnaphthylamine (1-AN) fluorescent probe in phospholipid bilayer and red blood cell (RBC) membranes have been studied. It is shown that the electronic spectra of the probe in model-membranes are inhomogeneously broadened. In contrast to low-molecular weight solvents, there are two reasons for inhomogeneous broadening. The first is connected with different levels of location of probe molecules in the membrane. Inhomogeneous broadening due to the first factor has a static character. The second reason is similar to that of solutions and linked with fluctuations of solvate structure. This type of broadening has a dynamic character. The process of intermolecular relaxation in membranes is accompanied by the release of the free energy excess, which results in wavelength-dependent rotation of probe.     

Spectral properties of dye lasers

Starting from conventional rate equations describing the multimode operation of a laser with a broad homogeneous emission line, a system of approximately valid equations, suitable for both analytical and numerical studies of the spectral properties of laser radiation not too far from threshold, has been derived by introducing equations of motion for the spatial Fourier components of the inversion densityN(z, t), thus replacing the equation of motion forN(z, t) itself. Analytical solutions for steady-state operation were found and physically discussed in the following cases: (a) ring laser, (b) jet-stream laser with the active medium positioned either near one of the (Fabry-Perot) resonator mirrors or in the centre of the resonator, and (c) laser with a Fabry-Perot resonator completely filled with the active medium. The spectra thus calculated indicate that spatial hole burning is most efficient in providing mode co-existence in configuration (c), where it gives rise to a significant bandwidth. It is of minor importance, however, in case (b), where the spectrum differs only slightly from that of a ring laser, which is clearly free from hole-burning effects.     

Similarities in electronic properties of organic charge-transfer solids and layered cobaltates

The apparently counterintuitive carrier concentration-dependent electronic properties of layered cobaltates have attracted wide interest. Here we point out that very similar carrier-concentration dependence has previously been noted in strongly correlated quasi-one dimensional (quasi-1D) organic charge-transfer solids. The normal states of both families can be understood, over the entire range of carrier concentration of interest, within the extended Hubbard Hamiltonian with significant intersite Coulomb interaction. As with the charge-transfer solids, superconductivity in the cobaltates appears to be limited to bandfilling of one-quarter. We point out further that there exist other families of correlated superconductors, such as spinels, where too strong correlations, geometric lattice frustration and bandfilling of one-quarter seem to be the essential features of the unconventional superconductors.     

Spectral properties of helical quantum wires

The spectrum of states of a helical quantum wire has been investigated theoretically. Eigenstates were found using an exact method based on alternating-direction implicit (ADI) evolution in imaginary time, for a wavefunction defined at discrete points in occupation number space and a nearest-neighbor interaction. A helical wire is a special case of a one-dimensional superlattice with an infinitesimal glide symmetry and associated glide-momentum quantum number. The continuous symmetry prevents the appearance of band gaps. Energy eigenstates have unquenched angular momentum--angular momentum increases with glide momentum. Band anharmonicity and angular momentum nonlinearity demonstrate effects of centrifugal acceleration.     

Spectral properties of the Anderson model

An investigation of the one particle spectrum of the (impurity-) Anderson model within the time ordered perturbation approach is presented. The approximation used includes all processes without crossing band electron lines and does not make use of the Brillouin-Wigner scheme. Foregoing treatments are thus generalized in essential points. Local self energies are determined by two coupled integral equations which are solved numerically. Numerical procedures and the validity of the approximation are thoroughly tested for the resonant level model, which deals with only one spin component and is exactly solvable. Calculated spectra for the Anderson model in all regimes of temperature and of local level position are discussed. A remarkable improvement over earlier attempts is found. Connection to the resonant level model is made by analytical continuation in the number of spin components. The approximation is placed into a general context of a conserved skeleton diagram expansion. It is pointed out how it can systematically be improved, and some exact formulas are derived.     

Spectral properties of the Kirkwood-Salsburg operator

A mathematically precise definition of the “infinite-volume” Kirkwood-Salsburg operator as a bounded linear operator in a Banach space is given. It is shown that this operator has a bounded inverse for a bounded, stable and regular pair potential. These facts are exploited to establish the connection between the Kirkwood-Salsburg and the Mayer-Montroll equations and to give a classification of the spectra and resolvents of the Kirkwood-Salsburg operator and of its inverse. The theorems proved in this article constitute a framework for the derivation of any more precise results for special potentials.     

Spectral properties of one dimensional quasi-crystals

In this paper we prove that the one dimensional Schrödinger operator onl ²(?) with potential given by: $$\upsilon (n) = \lambda \chi _{[1 - \alpha , 1[} (x + n\alpha )\alpha \notin \mathbb{Q}$$ has a Cantor spectrum of zero Lebesgue measure for any irrationalα and any λ>0. We can thus extend the Kotani result on the absence of absolutely continuous spectrum for this model, to all .     

Spectral properties of reduced Bloch Hamiltonians

Bloch Hamiltonians are defined, and the existence of bands is proven for a large class of periodic operators. The results are strong enough to include most of the reasonable physical models of a single electron in crystals. A notable exception is the Dirac Bloch Hamiltonian for a Coulombic crystal with high charge. Properties of the Bloch waves are briefly described and it is shown that “simple” Bloch Hamiltonians do not have Bloch waves with a finite number of Fourier coefficients. The asymptotic distribution of the bands is determined, and it is shown that for a large class of Hamiltonians, it is determined by the kinetic energy alone.     

Competition between charge-transfer exciton dissociation and direct photocarrier generation in molecular donor-acceptor compounds

The interfacial charge-separation and photovoltaic characteristics of a molecular donor-acceptor charge-transfer compound were examined. Measurements of laser beam-induced currents on the single crystals allowed selective detection of hole and electron photocurrents through the metal-semiconductor interfaces. This method also reveals the exceptionally long diffusion length of 20 μm in the crystal. The transition from charge-transfer exciton dissociation to direct photocarrier generation is discussed on the basis of the photon-energy-dependent diffusion length and photon-to-current conversion spectrum.     

One-dimensional fluctuating nanodomains in the charge-transfer molecular system TTF-CA and their first-order crystallization

We report on the direct observation by x-ray diffuse scattering measurements of thermally induced one-dimensional nanoscale ordered fluctuations in the mixed-stack charge-transfer molecular system tetrathiafulvalene-p chloranil (TTF-CA), the prototype for the neutral-ionic phase transition. The unusual physical properties of this compound are considered to be driven by such one-dimensional excitations. The results are discussed in relation to previous experimental and theoretical experiments both at thermal equilibrium and under light irradiation.