Karl-Heinz Etzbach

DESIGN, SYNTHESIS, AND EVALUATION OF A DYE LIBRARY : GLASS-FORMING AND SOLID-STATE LUMINESCENT MEROCYANINES FOR FUNCTIONAL MATERIALS

A highly efficient multicomponent reaction based on the little-known formylating agent dimethylformamide in acetic anhydride led to a multitude of dyes of the indoline (1) and of the thiazole type (2), whose systematic evaluation revealed desired and surprising solid-state properties.

Photopolymerization and transport properties of liquid crystalline triphenylenes

Abstract The synthesis of polymerizable triphenylene derivatives with acrylate groups is described. The thermal properties and the photoconductive properties of the discotic monomers as well as of the polymers is investigated. In the mesophase typically photoinduced hole conductivity with a charge carrier mobility exceeding a value of 10−4 cm2/Vs is observed with conventional time-of-flight (TOF) techniques. Different conditions for the photopolymerization of the acrylates in the mesophase are compared. The influence of the photoinitiators and the polymerization on the mesomorphic behavior and on the hole conductivity is described. Already the presence of small amounts of photoinitiator influences the packing within the mesophase. The polymerization further decreases the order and creates defects. This results in an at least one order of magnitude reduced charge carrier mobility at room temperature, compared to the monomer.

ELECTRONIC PROPERTIES OF DISCOTIC LC-MATERIALS

Abstract We have made extensive studies of the charge-carrier mobilities in the discotic hexagonal mesophases of triphenylene-based discotic liquid crystals. Using the time-of-flight technique, transient photocurrents were measured yielding charge-carrier mobilities for various electric fields and temperatures. Starting from promising results obtained with the monomeric discotic liquid crystalline model compound hexapentyloxytriphenylene (H5T), we synthesized a “discotic twin” with two triphenylene units linked together by a suitable spacer. Additionally, we synthesized a discotic liquid crystalline oligomer consisting of four triphenylene units which are bound to a flexible cyclosiloxane ring. In the dimer and in the oligomer the discotic mesophase can be maintained in a discotic glass. Our data show that in both H5T as well as in the dimer and in the oligomer hole mobilities on the order of magnitude of 10−3cm2/Vs can be reached. Since the mobilities obtained in the oligomeric compounds are comparable t...

Comparative Dielectric Investigations of Liquid Crystalline Oligomers and Monomers

Abstract Dielectric relaxation times and the static dielectric behaviour of monomers and oligomers with definite chemical structure are compared with each other.