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Klaus Meerholz

Publications and source records attributed to Klaus Meerholz.

7 recordsLinked to original sources
PubMed2003

Highly substituted azulene dyes as multifunctional NLO and electron-transfer compounds.

Two highly substituted azulene derivatives were synthesised by Pd-mediated dimerisation from the corresponding tolan species. One azulene derivative (2) has donor functionalities (dianisylaminophenyl and dianisylamino) in the 1-, 2-, 3- and 6-positions, while the other (1) has donors (dianisylaminophenyl) in the 2- and 6-positions and acceptors (nitrophenyl) in the 1- and 3-positions. Each azulene derivative shows strong bond length alternation in the solid state, determined by X-ray crystal analysis, and an intense CT band around 450-500 nm in its UV/Vis spectrum. The first-order hyperpolarisability of 1 and of 2 was measured by hyper-Rayleigh scattering and is about that of disperse red DR1. Both azulene derivatives show multiple oxidation processes. The intramolecular adiabatic ET behaviour of the mixed valence radical cations of 1 and of 2 was investigated by UV/Vis/NIR spectroelectrochemistry. The intervalence-CT band of 1(+) could be analysed by the Generalised Mulliken-Hush theory, which yields an electronic coupling V=1140 cm(-1) for the optically induced adiabatic hole transfer.

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PubMed2003

Multi-colour organic light-emitting displays by solution processing.

Organic light-emitting diodes (OLEDs) show promise for applications as high-quality self-emissive displays for portable devices such as cellular phones and personal organizers. Although monochrome operation is sufficient for some applications, the extension to multi-colour devices--such as RGB (red, green, blue) matrix displays--could greatly enhance their technological impact. Multi-colour OLEDs have been successfully fabricated by vacuum deposition of small electroluminescent molecules, but solution processing of larger molecules (electroluminescent polymers) would result in a cheaper and simpler manufacturing process. However, it has proved difficult to combine the solution processing approach with the high-resolution patterning techniques required to produce a pixelated display. Recent attempts have focused on the modification of standard printing techniques, such as screen printing and ink jetting, but those still have technical drawbacks. Here we report a class of electroluminescent polymers that can be patterned in a way similar to standard photoresist materials--soluble polymers with oxetane sidegroups that can be crosslinked photochemically to produce insoluble polymer networks in desired areas. The resolution of the process is sufficient to fabricate pixelated matrix displays. Consecutive deposition of polymers that are luminescent in each of the three RGB colours yielded a device with efficiencies comparable to state-of-the-art OLEDs and even slightly reduced onset voltages.

Journal Article↗
PubMed2002

Near-infrared sensitivity enhancement of photorefractive polymer composites by pre-illumination.

Among the various applications for reversible holographic storage media, a particularly interesting one is time-gated holographic imaging (TGHI). This technique could provide a noninvasive medical diagnosis tool, related to optical coherence tomography. In this technique, biological samples are illuminated within their transparency window with near-infrared light, and information about subsurface features is obtained by a detection method that distinguishes between reflected photons originating from a certain depth and those scattered from various depths. Such an application requires reversible holographic storage media with very high sensitivity in the near-infrared. Photorefractive materials, in particular certain amorphous organic systems, are in principle promising candidate media, but their sensitivity has so far been too low, mainly owing to their long response times in the near-infrared. Here we introduce an organic photorefractive material -- a composite based on the poly(arylene vinylene) copolymer TPD-PPV -- that exhibits favourable near-infrared characteristics. We show that pre-illumination of this material at a shorter wavelength before holographic recording improves the response time by a factor of 40. This process was found to be reversible. We demonstrate multiple holographic recording with this technique at video rate under practical conditions.

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PubMed2002

Chromophore design for photorefractive organic materials.

During the last years, significant progress has been achieved in understanding the mechanism of the photorefractive effect in amorphous organic materials. New chromophores could be devised which provided a substantial increase in the electrooptical response and lead to photorefractive materials with unprecedented refractive index modulation (delta n = 10(-2) at E = 28 V micron-1) and two-beam coupling gain. These improvements could only be accomplished by optimizing the electronic structure of highly conjugated merocyanine dyes to perfectly balanced dyes in the charge resonance limit (such as aminothienyl oxopyridone (ATOP) and indoline dimethine oxopyridone (IDOP) derivatives), considering effects of supramolecular ordering (dipolar aggregation), and adjusting the compatibility of the dyes to photoconducting polymers (like poly-N-vinylcarbazole). In particular, optimized glass-forming dyes (such as 2BNCM and ATOP-4) combine the dual functionalities of charge transport and electrooptical response and exhibit photorefractivity even in absence of any additional photoconductor.

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