Arno Böhm

Liquid crystalline coronene derivatives with extraordinary fluorescence properties

Tempering of polystyrene films containing the novel liquid crystalline coronenebis(dicarboximide)s 2, which are formed by an easy route from perylene-3,4;9,10-tetracarboxylic dianhydride (1), leads to a shift of the emission within a few seconds. This could be used for dot-by-dot coloring and thus optical displays. The photoluminescence properties of 2 in the solid matrix are dependent on the nature of the aggregates formed.

MIDI - The 10 mu m instrument on the VLTI

After more than five years of preparation, the mid-infrared interferometric instrument MIDI has been transported to Paranal where it will undergo testing and commissioning on theVery Large Telescope Interferometer VLTI from the end of 2002through large part of this year 2003. Thereafter it will be available as a user instrument to perform interferometric observations over the8 μm–13 μm wavelength range, with a spatial resolution of typically 20 milliarcsec, a spectral resolution of up to 250, and an anticipated point source sensitivity of N = 3–4 mag or 1–2.5 Jy for self –fringe tracking, which will be the only observing mode during the first months of operation. We describe the layout of the instrument, laboratory tests, and expected performance, both for broadband and spectrally resolved observing modes. We also briefly outline the planned guaranteed time observations.

Quaterrylenebis(dicarboximide)s: near infrared absorbing and emitting dyes

New ladder-type chromophores, the quaterrylenebis(dicarboxdiimide)s 2, 18 and 23, have been synthesised which, despite their extended π-system, exhibit good solubility in organic solvents and film forming properties when adequately substituted. These unprecedented dyes, which absorb and even emit light in the NIR window, are also characterized by oustanding chemical, thermal and photochemical stability with regard to their absorption range. The potential formation of J-aggregates in strongly acidic media has been investigated and has been ruled out by combined 1 H NMR and UV-VIS-NIR spectroscopy experiments. In addition, their photophysical and electrochemical characteristics have been explored and are discussed.

New Thermotropic Dyes Based on Amino‐Substituted Perylendicarboximides

We report on an facile multigram synthesis of novel thermotropic dyes. When these dyes are heated they undergo an irreversible change from a photostable primary color to a photostable secondary color. Our concept is based on thermally initiated fragmentation to afford a chromophore with a donor and an acceptor substituent. We used thermally unstable alkoxycarbonyl substituents as masking groups for the strong electron-donating primary amino group attached to a perylenedicarboximide chromophore. On heating the alkoxycarbonylated dyes, the parent primary amino-functionalized dyes are regenerated in almost quantitative yield by elimination of an alkene and carbon dioxide. This process is accompanied by a large bathochromic shift in the absorption spectrum. Variations in the alkoxycarbonyl substitution lead to different reaction temperatures for the color change in this class of materials. The synthetic route used for the amino-functionalized perylene imide dyes involves the palladium-catalyzed amination of bromo-substituted precursors.

Eletron-transfer induced valence isomerization of 1,2-distyrylbenzene

Abstract Upon electron transfer 1,2-distyrylbenzene 2 undergoes a valence isomerization giving rise to an indane derivative. This process is controlled by the ion-pair structures of the anionic intermediates and differs from the photochemically induced rearrangement.