03 Fakultät Chemie
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Item Open Access The mechanism of intramolecular energy transfer in terminally substituted polyene molecules(1993) Holl, Norbert; Port, Helmut; Wolf, Hans Christoph; Strobel, Hartmut; Effenberger, FranzAbsorption, fluorescence and excitation spectra of different terminally substituted polyenes have been recorded in the UV-Vis region. The observed intramolecular unidirectional energy transfer from a donor substituent to an acceptor at the other end of the chain is influenced but not inhibited by incorporation of a spacer into the polyene chain. In molecules without a spacer, internal conversion within the supermolecule can explain the observed transfer of energy. In molecules with a spacer interrupting the polyene chain the observed intramolecular energy transfer can be explained in terms of Förster transfer.Item Open Access Highly ordered LB films of DHAP : a donor acceptor substituted polyene(1993) Schmelzer, Michael; Roth, Siegmar; Niesert, Claus-Peter; Effenberger, Franz; Li, Rui ChengThe donor acceptor substituted polyene 5-(4-dihexadecylaminophenyl)-2-methyl-2,4-pentadienal (DHAP) is - due to its amphiphilic nature - a promising candidate for the Langmuir-Blodgett (LB) technique. The molecule was studied as a monolayer on a pure water surface under argon atmosphere. Monolayers and multilayers were transfered onto solid support. The films showed a high degree of order in the monolayer as well as in thick multilayers. LB films were investigated with polarisation dependent UV/VIS absorption spectroscopy. The film spectra showed additional absorption peaks which were not present in the spectra of the molecules in solution. The relative peak intensities were highly dependent on the orientation of the electric field vector with respect to the substrate normal. To get a detailed picture of the arrangement of the films on the molecular level, we studied the polarisation dependence of the FTIR spectra in different experimental set-ups. The spectra showed a perpendicular orientation of the conjugated system with respect to the substrate, whereas the backbone of the saturated hydrocarbon chains showed a medium tilt angle of 20.0° with respect to the substrate normal. X-ray small angle diffraction measurements were applied to investigate the thickness of the LB layers. From the position of the Bragg peaks, a thickness of 5.45 nm per bilayer can be calculated, in agreement with a bilayer model showing different molecular alignment of the molecules transferred during upstroke and downstroke.Item Open Access Localized states in anthrylpolyenes : influence of geometry(1990) Heine, Barbara; Sigmund, Ernst; Maier, Stefan; Port, Helmut; Wolf, Hans Christoph; Effenberger, Franz; Schlosser, HubertCombining group theoretical arguments and (extended) Hückel calculations, it is shown that terminally anthryl-substituted polyenes exhibit states almost completely localized at the substituents. These localized states are related to characteristic optical transitions in anthracene which also are observed in anthrylpolyenes independent of the length of the polyene chain.Item Open Access Lowest excited singlet states of α-9-anthrylpolyenes(1993) Holl, Norbert; Emele, Peter; Port, Helmut; Wolf, Hans Christoph; Strobel, Hartmut; Kesmarszky, Thomas; Effenberger, FranzProperties of the electronically excited states of α-9-anthrylpolyenes are studied in n-hexane solutions by using optical absorption, emission and fluorescence excitation spectroscopy. The absorption spectra reveal a complex structure with contributions of both anthracene and polyene type bands but also of bands with mixed anthracence/polyene character. Small amounts of remaining impurities are chemically not separable but can be detected via fluorescence measurements. By computer-aided decomposition of spectra measured under variable selective excitation the actual, clearly chain-length dependent, fluorescences could be obtained.