Excitation transfer between components of molecular layers of cyanine compounds

Using the example of layers of symmetric polymethine dyes, we have studied the optical excitation energy transfer processes between nanocomponents of a molecular layer. The fluorescence yields and life-times of excited states of monomeric stereoisomers have been estimated, and the stereoisomerization yields have been determined. We show that the excitation transfer yield between the S ₁ states of monomeric stereoisomers (tens of percent) is considerably higher than the fluorescence yield (several percent) and depends on the structure of terminal groups of the molecule.     

Optical properties and component composition of layers of cyanine dyes on dielectric supports: influence of asymmetry of the molecular electron density distribution

The component composition of molecular layers of dicarbocyanine dyes of cationic type on glass is determined by the absorption spectroscopy methods. For symmetric and asymmetric molecules the component composition depends on the chemical structure of a molecule and its interaction with the substrate, which are responsible for the electron density distribution in a molecule. The interaction with the substrate depends on the thickness of a layer and the orientation of a layer molecule on the substrate. The increase in the separation between the molecule and the substrate in thicker layers decreases the interaction with the substrate and the asymmetry of a molecule. In symmetric and slightly asymmetric dyes the value of the charge difference on the end groups decreases with increasing layer thickness, whereas in dyes with a large asymmetry, both the value and the sign of the charge difference change. The above results are confirmed by data on the computer simulation of the charge distribution in a dicarbocyanine cation upon its interaction with the oxygen anion on the substrate.     

Molecular dynamics simulation studies of the influence of imidazolium structure on the properties of imidazolium/azide ionic liquids

Atomistic molecular dynamics simulations were performed on 1-butyl-3-methyl-imidazolium azide [bmim][N(3)], 1-butyl-2,3-dimethylimidazolium azide [bmmim][N(3)], and 1-butynyl-3-methyl-imidazolium azide [bumim][N(3)] ionic liquids. The many-body polarizable APPLE&P force field was augmented with parameters for the azide anion and the bumim cation. Good agreement between the experimentally determined and simulated crystal structure of [bumim][N(3)] as well as the liquid-state density and ionic conductivity of [bmmim][N(3)] were found. Methylation of bmim (yielding bmmim) resulted in dramatic changes in ion structuring in the liquid and slowing of ion motion. Conversely, replacing the butyl group of bmim with the smaller 2-butynyl group resulted in an increase of ion dynamics.     

THE MITRA‐WAN FORESTRY MODEL: A DISCRETE‐TIME OPTIMAL CONTROL PROBLEM

In this paper, we present some new properties of the Mitra‐Wan forestry model written as a discrete‐time optimal control problem. For this problem, the set of stationary states is characterized. For the optimal long‐run management, we consider the following optimality criteria: average optimality, good control policies, bias optimality, and overtaking optimality. We establish relationships between these criteria and show that the value of average optimal policies is constant and equals the value in the optimal stationary state.     

Identification of Absorption Bands of Monomers and Aggregates in a Layer of Cyanine Dye and Determination of the Orientation of Molecules

Optics and Spectroscopy - The problem of allocating bands of individual monomers or aggregates of the absorption spectrum of a multicomponent structure arises in the study of molecular layers or...     

Cylindrical bending of an elastic rectangular sandwich plate on a deformable foundation

Cylindrical bending of an elastic rectangular sandwich plate having a rigid filler and resting on an elastic foundation is considered. To describe the kinematics of the plate, asymmetric across its thickness, the hypotheses of broken normal are assumed. The reaction of the foundation is described by the Winkler model. A system of equilibrium equations is derived, and its exact solution is obtained in terms of displacements. A numerical analysis of the solution is presented.     

Deformation of a composite plate on an elastic foundation by local loads

Bending of an elastic annular composite plate with a light filler lying on an elastic foundation is considered. The plate is subjected to local loads. To describe the kinematics of the package, asymmetric across its thickness, the hypotheses of broken normal is accepted. The reaction of foundation is described based on the Winkler model. A system of equilibrium equations is constructed, and its exact solution in displacements is found. Numerical solutions for a metal-polymer sandwich plate are presented. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 1, pp. 109–120, January–February, 2007.     

Optical properties of polymethine molecules incorporated into a macroscopic set of parallel nanotubes

The structural properties of polymethine molecules incorporated into nanofibers of chrysotile asbestos have been studied by absorption-spectroscopy methods. These experiments have shown that, in chrysotile nanotubes, monomeric, all-trans- and cis-isomers, dimers and J aggregates can be observed. Upon incorporation of a dye from weakly concentrated solutions, monomeric forms of polymethine molecules, extended chromophores of which are oriented along parallel asbestos nanotubes, are predominantly observed. The hybrid material under investigation may be of interest for applied problems.     

Formation mechanisms of equilibrium component composition of molecular layers of polymethine dyes

We study the concentration dependences for the absorption spectra and component composition of molecular layers from three homologous series of symmetric polymethine dyes of different electron-donating ability of their terminal heterocyclic groups. We find that a change in the layer thickness leads to a change in the width and position of the spectrum due to a change in the number of absorption bands. The number of bands of monomers increases with increasing chain length and electron-donating ability. The concentration ratio of monomers and associated forms depends on the spatial orientation of molecules in the layer. The electron-donating ability of terminal groups affects the angle between the chromophores of molecules that form a dimer and the intensity ratio between the short- and long-wavelength absorption bands of dimers. We conclude that the effect of the thickness of the layer on its spectral parameters is determined by the degree of intramolecular electron asymmetry that arises as a result of the interaction of chemically symmetric molecules with charges of the substrate surface and upon intermolecular interaction. This asymmetry leads to changes in free energies of ground states of monomeric molecules and, as a consequence, to an increase in equilibrium concentrations of cis-stereoisomeric forms in the layer.