Transfer of electronic excitation energy between randomly mixed dye molecules in the channels of zeolite L

Host-guest materials containing strongly fluorescent donor and acceptor molecules have been prepared. Fine-tuning of the donor to acceptor distance in this material allows beautiful visible and quantitative observation of electronic excitation energy transfer phenomena. Oxonine and pyronine have been used as guest molecules and zeolite L as host. The dyes have been inserted by ion exchange. Stationary state and time-resolved experiments have been carried out with zeolite crystals of 300 and 700 nm size in the dye concentration range of 10(-4) mol/L up to 0.042 mol/L. The fluorescence decay of the donor and the pumping of the acceptor via energy transfer, which can be well observed, became faster with increasing loading. The behavior of the system follows requirements expected for F?rster energy transfer material.     

Preparation of asymmetric bilayer-vesicles with inner and outer monolayers composed of different amphiphilic molecules

Asymmetric vesicles were prepared layer by layer from reverse micelles. The aqueous solution was first entrapped into reverse micelles prepared from lipid, then these reverse micelles penetrated the monolayer formed by another kind of amphiphilic agent at organic solvent/water interface by centrifugation and were assembled spontaneously by the second layer to form asymmetric vesicles. In general, the diameters of the vesicles ranged from 30 to 100 nm. A fluorescein quenching experiment showed that asymmetric vesicles with the inner layer being lipid and the outer layer being single-chain amphiphilic molecules, [(bpy)₂ Ru(diazafluorenone) (CH₂)₁₅CH₃](PF₆)₂, were successfully prepared. The half-life of flip–flop of the amphiphilic molecules between inner and outer layers was estimated to be about 17 days.     

Synthesis and properties of a microtube photocatalyst with photoactive inner surface and inert outer surface

Synthesis of a photocatalyst with a novel particle form, its photoactivity, and the degradation of polyvinyl alcohol containing the photocatalyst were studied in detail. A microtube photocatalyst with titanium dioxide particles supported on the inner surface of the microtube was synthesized by adding fine titanium dioxide particles in the formation process of basic magnesium carbonate microtube. The photoactivity of the microtube photocatalyst was confirmed from the decomposition of 2-propanol under blacklight irradiation. Moreover, the microtube photocatalyst was found to cause no degradation of polyvinyl alcohol, whereas, it decomposed 2-propanol with its photoactivity when impregnated in a polyvinyl alcohol foam. This fact was considered to be derived from the unique structure of the microtube photocatalyst, which has a photoactive inner surface with titanium dioxide and an inert outer surface of basic magnesium carbonate.     

Modeling the surface of polystyrene and the adsorption of dye molecules on this surface

Models of the structures of complexes of the Nile red dye (NR) molecule on the surface of various types of polystyrene (PS) were constructed by molecular dynamics (MD). The surface of a polystyrene film and the surfaces of clumps of isolated polystyrene chains were examined as surfaces. The film and the clumps were obtained as a result of molecular-dynamics trajectories. The atomistic version of molecular dynamics was used. The surface of the film was comparatively uniform, and the clumps were irregular ellipsoids with varied local surface form. The variety of the surface forms makes it possible to obtain complexes of PS with local environments having different structures. A method of constructing the solvent-accessible surface (SAS) was proposed as method of evaluating the potential sensor characteristics of the material. In the PS clumps the NR molecule is almost completely submerged in the upper layer, while in the film the aromatic fragment of the dye is partly accessible to the analyte.     

Characterizing the fluorescence intermittency and photobleaching kinetics of dye molecules immobilized on a glass surface

The blinking behavior of single Atto565 molecules on a glass surface is studied under air or nitrogen atmospheres using confocal microscopy. The broad distributions for both on- and off-time durations obey power law kinetics that are rationalized using a charge tunneling model. In this case, a charge is transferred from the Atto565 molecule to localized states found on the glass surface. Subsequent charge recombination by back charge tunneling from trap to Atto565 cation (i.e., dark state) restores the fluorescence. The off-time distribution is independent of excitation intensity (I), whereas the on-time distribution exhibits a power law exponent that varies with I. Two pathways have been identified to lead to the formation of the radical dark state. The first involves direct charge tunneling from the excited singlet S1 state to charge traps in the surrounding matrix, and the second requires charge ejection from the triplet T1 state after intersystem crossing from S1. Monte Carlo simulation studies complement the two-pathway model. Photobleaching curves of both single and ensemble molecules do not exhibit monoexponential decays suggesting complex bleaching dynamics arising from triplet and radical states.     

On the inner and outer radial density functions

Starting from the two-electron radial density D ₂(r ₁,r ₂), a generalized partitioning of the one-electron radial density function D(r) into two component densities D _a (r) and D _b (r) is discussed for many-electron systems. The literature partitioning (Koga and Matsuyama Theor Chem Acc 115:59, 2006) of D(r) into the inner D _<(r) and outer D _>(r) radial densities is shown to minimize the average variance of the two component density functions D _a (r) and D _b (r). It is also found that the average radial separation halved, , constitutes a lower bound to the standard deviation σ of D(r).     

A new substrate for surface enhanced Raman scattering of dye Sudan molecules

A new SERS substrate was prepared using electro-polishing aluminum foils. Based on these high active SERS systems, surface enhanced Raman scattering (SERS) of Azo Dye Sudan were performed and carefully studied based on this highly active SERS substrate. High quality SERS spectra were obtained, which indicates that this kind of coarse aluminum foils is an active SERS substrate. Numbers of additional modes were presented, as well as some split peaks, which may be a consequence of symmetry lowering.     

Short- and long-range behavior of the inner and outer densities

We report the short- and long-range behavior of the inner $ \rho_<(r) $ and outer $ \rho_>(r) $ densities, which result from a rigorous partitioning of the spherically averaged one-electron density $ \rho(r) $ in many-electron atoms. It is found that for a small r, $ \rho_<(r) $ has one-electron nature but $ \rho_>(r) $ has two-electron nature. For a large r, however, the opposite is true.     

Bile acid-based cage compounds with lipophilic outer shells and inner cavities

The uniquely functionalized steroid-based cyclodimers 4, cis-5, and trans-5 have been synthesized and fully characterized.The cyclodimer 5, with a cis-trans ratio of 3:1, is obtained by coupling the terminal alkenes of two 4-pentenoate groups on a cyclodimer 4 via Grubbs' intramolecular ring-closing metathesis. The crystal structure shows cis-5 to be a cagelike cyclic oligomer bridged by the flexible oct-4-enedioate link.     

Spectral luminescent study of orientation states of dye molecules adsorbed on a nonuniform surface

Brownian reorientation motion of molecules results in an equilibrium of orientation states of adsorbed molecules. The character of the orientation equilibrium depends on the total concentration of adsorbed molecules. Since optical properties of molecules are sensitive to the intermolecular interaction with an adsorbent, each orientation state has an individual luminescence spectrum. A change in the equilibrium results in complicated concentration and temperature dependences of the spectra of adsorbed molecules. These dependences have been experimentally observed for several dyes adsorbed on microporous silicate glass. Equilibrium constants and fractal dimensions of the spatial distribution of dye molecules in porous matrices have been determined.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1284–1288, July, 1995.     

Influence of dye molecules on the birefringence of liquid crystal mixtures at near infrared frequencies

The optical properties of nematic liquid crystals have been extensively exploited in the production of devices working in the visible range of the spectrum. These same properties can be employed to make devices that function in the near infrared as required for telecommunications applications. However, it is generally observed that the birefringence of liquid crystal mixtures decreases with increasing wavelength, making it important to identify new materials, optimized for use in the near infrared region. One route to high birefringence is to operate close to an absorption band edge, which in the present context implies choosing highly conjugated materials which are potentially colored and, thus, not suited to traditional display applications. In this paper we explore the usefulness of dye molecules as birefringence enhancers in mixtures with conventional nematic liquid crystals. The optical properties, in particular, the absorption edge, polarizability, and birefringence, of families of known dyes are calculated at optical (589 nm) and infrared (1550 nm) wavelengths, using electronic density functional theory. We demonstrate the expected correlation between the proximity of the absorption edge and the magnitude of the birefringence, and estimate the birefringence enhancement occurring when each dye is incorporated in a guest-host system.     

水溶性杯芳烃对染料客体分子的包结配位作用

研究了水溶性的杯[n]芳烃磺酸盐(n=4,6,8)及杯[6]芳烃磺酸盐的烷基化衍生物在25.0℃对几种染料客体分子的包结配位作用,发现杯[n]芳烃磺酸盐均使客体的荧光强度降低,而在其下缘的烷基化衍生物却使客体的荧光强度增强,从光物理行为对这些结果进行了解释。由荧光光谱分光光度滴定技术确定了25.0℃时所形成配合物的稳定常数,讨论了其分子识别性质。     

Quadratic hyperpolarizabilities of nitro-substituted pseudo-linear dye molecules with ethylenic and azo bridges

Second-order hyperpolarizabilities (β) and gas-phase transition energies (E) of the para-disubstituted benzene, stilbene and azobenzene derivatives are calculated by the semi-empirical self-consistent-field molecular orbit (SCF MO) method in the Pariser-Parr-Pople (PPP) approximation using a sum-over-state's procedure with singly excited states. The calculated zero-frequency β (β⁰_VEC) values for all the derivatives are directly proportional to their 1/E² values. The usefulness of mixing ethylenic and azo bridges in long π-conjugated molecules is proposed in order to obtain large β values, by taking the difference between the electronic natures of these bridges into account. © 1996 John Wiley & Sons, Inc.     

Thermoanalytical study of inner and outer residue of coffee harvest

The better use of agricultural residues is expected, when they are mostly disposed of improperly and it is often burned in the natural environment. This study of the thermal decomposition of residues was performed from the coffee crop for energy purposes and in this case was used thermal analysis techniques for such assessment. The TG/DTG and DSC curves showed that the thermal decomposition occurs in four consecutive events and it is predominantly exothermic. The first mass loss evidenced in TG/DTG curves has an endothermic peak in DSC curve, which it can be associated with the water liberation of the material. This first thermal event also can be related to the liberation of volatile compounds present in the sample, which is also corroborated by the endothermic peak. The other events of mass loss are related with the thermal decomposition of the material. This decomposition has an exothermic behavior, which is positively applied to the main aim of this scientific research: the coffee straw use like biomass energy font. The thermoanalytical techniques were satisfactory in the characterization of this material.