Browsing by Author "Port, Helmut"

Now showing 1 - 10 of 10

Open Access
Dual fluorescence of 9-anthryl-substituted oligothiophenes in nonpolar environment
(1994) Emele, Peter; Meyer, Dirk U.; Holl, Norbert; Port, Helmut; Wolf, Hans Christoph; Würthner, Frank; Bäuerle, Peter; Effenberger, Franz
9-Anthryl-oligothiophenes (9A-Tn, n = 1–4) have been studied in n-hexane solution between helium and room temperature using absorption, fluorescence emission and excitation spectra and time resolved fluorescence measurements. These compounds are reference systems for studies on intramolecular energy and charge transfer in donor/acceptor-substituted conjugated chain molecules. The absorption spectra show contribution of both substituents anthracene and oligothiophene, but no additional bands due to mixed electronic states. Dual fluorescence is observed at Tgreater-or-equal, slanted 120 K for the compounds 9A-Tn (n = 1–3), but not for 9A-T4. Time resolved spectroscopy reveals a dynamical coupling between the two emission components whose relative quantum yields are strongly temperature dependent. The occurrence of the dual fluorescence is explained by an intramolecular torsional motion between the two molecular subunits.
Open Access
Energy transfer through conjugated polyenes
(1989) Maier, Stefan; Port, Helmut; Wolf, Hans Christoph; Effenberger, Franz; Schlosser, Hubert
From an analysis of absorption, fluorescence and excitation spectra of linear polyene molecules with 4 to 13 double bonds and one or two aromatic substituents at the chain ends we conclude that the aromatic substituents can be excited individually, and that intramolecular energy transfer from one end group via the polyene to the other end group is possible.
Open Access
Fulgides as switches for intramolecular energy transfer
(1993) Walz, Jochen; Ulrich, Karl; Port, Helmut; Wolf, Hans Christoph; Wonner, Johann; Effenberger, Franz
In a molecular unit which is a donor-fulgimide-acceptor triade, the possibility of an intramolecular energy transfer from donor to acceptor depends upon the isomer configuration of the photochromic fulgimide. It is shown that a switching on and off of this intramolecular energy transfer is possible by photoinduced shifting of the fulgimide levels between a trap and an antitrap function.
Open Access
Intramolecular energy transfer through linear polyenes : effect of spacers
(1990) Blessing, Gerd; Holl, Norbert; Port, Helmut; Wolf, Hans Christoph; Effenberger, Franz; Kesmarszky, Thomas; Schlosser, Hubert
The optical properties of linear polyenes terminally substituted with different molecules (mainly anthryl- and TPP-substituents) have been studied. Bicyclic spacers within the polyene chain affect the quantum yields but do not interrupt intramolecular energy transfer between the endgroups.
Open Access
Localized states in anthrylpolyenes : influence of geometry
(1990) Heine, Barbara; Sigmund, Ernst; Maier, Stefan; Port, Helmut; Wolf, Hans Christoph; Effenberger, Franz; Schlosser, Hubert
Combining 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.
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, Franz
Properties 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.
Open Access
The mechanism of intramolecular energy transfer in terminally substituted polyene molecules
(1993) Holl, Norbert; Port, Helmut; Wolf, Hans Christoph; Strobel, Hartmut; Effenberger, Franz
Absorption, 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.
Open Access
Photochromic thiophenefulgides : photokinetics of two isopropyl derivatives
(1991) Ulrich, Karl; Port, Helmut; Wolf, Hans Christoph; Wonner, Johann; Effenberger, Franz; Ilge, Hans-Dieter
For two photochromic isopropyl-thiophenefulgides a complete photokinetic analysis is given. For one compound (5b), the partial quantum yield for the colouring process (ΦEC = 54%) is the highest value found for thiophenefulgides. EZ-isomerisations do not play an important role. The colouring quantum yield is temperature independent down to 20 K, whereas bleaching requires little thermal activation. In case of an adamantylidene substituted isopropyl-thiophenefulgide (5c), the bleaching efficiency (ΦCE = 31%) is very high. Upon heating of the cyclic products, thermal bleaching occurs with an activation energy of 1 eV.
Open Access
Synthesen und optische Eigenschaften endständig substituierter konjugierter Polyene
(1988) Effenberger, Franz; Schlosser, Hubert; Bäuerle, Peter; Maier, Stefan; Port, Helmut; Wolf, Hans Christoph
Wir berichten hier über die Synthese konjugierter Polyene unterschiedlicher Länge, die endständig Substituenten tragen, deren spektroskopische Eigenschaften sich von denen der Polyenkette unterscheiden. Anhand von Absorptions-, Emissions- und Anregungsspektren werden die gezielte optische Anregung dieser Modellverbindungen und die Möglichkeiten eines intramolekularen Energietransports diskutiert.
Open Access
Synthesis and optical properties of terminally substituted conjugated polyenes
(1988) Effenberger, Franz; Schlosser, Hubert; Bäuerle, Peter; Maier, Stefan; Port, Helmut; Wolf, Hans Christoph
Long-chain, conjugated polyenes can function as molecular wires. This is shown by the photophysical properties of polyenes containing naphthyl, anthryl, and tetraphenylporphyrinyl (TPP) terminal groups. When the anthryl group in 1, which is obtainable by a sequence of Wittig reactions, is selectively excited, strong TPP emission is observed.