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Scanning tunneling microscopy (STM) was used to study physisorbed monolayers of 5-octadecyloxyisophthalic acid (C18ISA) and 5-[ω-(4‘-dodecyloxy-4-azobenzeneoxy)dodecyloxy]isophthalic acid (C12(AZO)C12ISA) at a liquid/graphite interface. The acquired STM images exhibit the molecular packing of the monolayers with submolecular resolution. Monolayers formed by codeposition of solvent molecules and C18ISA or C12(AZO)C12ISA molecules are found when 1-octanol and 1-undecanol are used as a solvent. The cis and trans isomers of C12(AZO)C12ISA, the reagent and reaction product of a reversible photoinduced reaction, are simultaneously present and are both structurally identified at the liquid/graphite interface.

The fluorescence anisotropy of two neutral and nonpolar molecules, 2,5,8,11-tetra-tert-butylperylene (TP) and 2,5,10,13-tetra-tert-butylterrylene (TT), is studied in a series of n-alcohols and alkanes. Both probes show an absorption band in the UV region and one in the visible region. The polarized fluorescence decay traces are globally analyzed over different excitation wavelengths. TP and TT can be modeled as oblate ellipsoids with essentially identical rotational correlation times. The anisotropy decay can well be approximated by a monoexponential model for both solvent series. The rotational correlation times (φ) vary linearly with viscosity (η) for both solvent series. Higher values for φ/η are reached in alkanes than in alcohols, the effect being more pronounced for TP than for TT. The predictions of the quasihydrodynamic models of Gierer−Wirtz and of Dote−Kivelson−Schwartz (DKS) are compared to the experimental data. Only the DKS model can predict qualitatively the experimental observations. The di...

Langmuir−Blodgett multilayer films were prepared from N,N‘-dioctadecyl rhodamine B (RB18) diluted in dioleoylphosphatidic acid (DOPA) or dipalmitoylphosphatidic acid (DPPA) with various mixing ratios. Surface pressure−area isotherms of monolayers of the two matrices were recorded. Absorption and fluorescence spectra and fluorescence decays of the multilayer samples of RB18 were further examined. The fluorescence decay curves of RB18 in the multilayer assemblies, determined using time-correlated single photon counting, were analyzed in the framework of several models leading to nonexponential decays: (1) multiexponential decay; (2) Gaussian distribution of rate constants; (3) stretched-exponential decay, characteristic of Forster energy transfer in self-similar fractal-like structures with a fractal dimensionality of

Upon investigation of the photoconductive properties of polycarbonate doped with 1,3-bis(dicyanomethylene)indans, a large, temperature independent quantum yield for charge generation was observed. The field and temperature dependence of the charge carrier mobility could be analyzed in the framework of the disorder model, developed by Bassler et al. The prefactor mobility was found to be of the same order of magnitude as that observed for hole transport materials with a comparable dipole moment. In the framework of the used disorder model, this relationship would suggest a dependence of the wave function decay constant on the molecular dipole moment. This would result in a material dependence of the prefactor mobility, which has also been found for other charge transport molecules.

Intermicellar Mobility of Probe and Quencher in Reverse Micelles Studied by Fluorescence Quenching

Hole mobilities have been measured in vapor deposited films of 5'-[4- [bis(4-ethylphenyl)amino]phenyl] N,N,N',N'-tetrakis(4-ethylphenyl)-1,1':3',1''-terphenyl-4,4''-diamine (p-pEFTP), a compound containing three donor functionalities per molecule. The results are described within the framework of a model based on disorder, due to Bassler and co-workers. The model is based on the assumption that charge transport occurs by hopping through a Gaussian distribution of localized states with superimposed positional disorder. The key parameters of the model are σ, the energy width of the hopping site manifold, and Σ, a parameter that describes the degree of positional disorder

Using optoacoustic spectroscopy, the radiationless decay processes of intramolecular exciplexes of ω-phenyl-α-N,N-dimethylaminoalkanes are investigated. Upon increase of the solvent polarity, the relative efficiency of the intersystem crossing process from the singlet exciplex to the locally excited triplet decreases compared to the efficiency of the internal conversion process. These results can be rationalized in the framework of the current electron-transfer theory and compared to the results obtained for other ω-aryl-α-N,N-dimethylaminoalkanes

Global analysis with the reference convolution method is used to study probe migration (using sodium 1-pyrenesulfonate) in fluorescence quenching (using N-tetradecylpyridinium chloride) in micellar solutions of CTAC molecules. The values of the quenching rate constant and mean aggregation number were obtained to show that the probe migration constant was a linear function of the micelle concentration. Analysis with a more hydrophobic probe revealed that it doesn`t migrate between micelles during its excited-state lifetime. 40 refs., 5 figs., 8 tabs.

Fluorescence quenching in monodisperse micelles with probe migration and Poisson-distributed quencher molecules is analyzed theoretically and by numerical simulation. An exact solution for the fluorescence decay is derived and expressed as a series of generalized self-convolution products of an Infelta-Tachiya type equation. Based on Almgren's approach and data analysis of synthetic sample decays, an approximated solution to the fluorescence decay is also derived

Anodic photocurrents are obtained upon excitation of xanthene dyes incorporated into Langmuir-Blodgett films deposited on SnO{sub 2}. The observed quantum yield of the photocurrent strongly depends upon the applied electrode potential, the regenerator (hydroquinone) concentration, and the pH of the electrolyte. The photocurrent is nearly independent of the chemical structure of the dye or the amount of dye incorporated in the monolayer. For 3,6-bis(N-ethyl-N-octadecyl)aminoxanthylium perchlorate (PYR18) and N,N{prime}-dioctadecylrhodamine 119 (RH18), the photocurrent action spectra resemble the absorption spectra of the mixed monolayer or a dilute solution of the dye in chloroform. Interactions between the chromophore and the cadmium arachidate matrix shift the spectral sensitization maximum of the surface-active bis(N-ethyl-N-octadecyl)rhodamine (RB18) to shorter wavelengths than the absorption maximum of the mixed monolayers or the action spectra of adsorbed rhodamine B. As observed for adsorbed rhodamine B the action spectra give no indication for the formation of sandwich dimers for RB18 and RH18. Analysis of Mott-Schottky plots obtained at low frequency indicates that decreasing the electrolyte pH leads to an anodic shift of the flat-band potential (E{sub fb}) and that the electrode is only partially covered by the deposited Langmuir-Blodgett film.

Solution numerique de l'equation de Poisson-Boltzmann dans un modele de cellule en vue d'obtenir le potentiel electrostatique d'une solution micellaire modele. Le systeme est choisi pour simuler une solution de laurylsulfate de sodium. On etudie la diffusion de cations mono- et divalents, et des especes neutres, en accord avec diverses particularites de la cellule. On discute le concept de liaison et en particulier, comment il participe a la description cinetique de l'extinction de la fluorescence par des ions antagonistes dans une solution micellaire