Peter Schuhmacher

Synthesis of New Functionalized Discotic Liquid Crystals for Photoconducting Aplications

Abstract The columnar structure of discotic liquid crystals has been shown to be well suited for electronic transport parallel to the columnar axis. To tailor the processibility and mesophase behavior of such materials, several hydroxytriphenylene derivatives were synthesized. These hydroxytriphenylenes can be converted into oligomers, networks or polymers. Further, they can be reduced to arenes which posses reactive sites for classical aromatic substitutions. A number of mixed tail triphenylene derivatives and fluorescent, low symmetry triphenylene discotic liquid crystals were synthesized and characterized.

Selective ether cleavages: simple routes yielding di- and tri-functional hexaalkoxytriphenylenes

Discotic hexasubstituted triphenylene derivatives represent a promising class of materials, e.g. with respect to their photoconductive properties. To tailor the processibility and mesophase behaviour of such materials specifically functionalized cores as precursor molecules for discotic oligomers, polymers and networks or amphiphiles are required. The paper presents various synthetic strategies, all based on selective ether cleavage methods, leading to new highly functionalized triphenylenes.

The synthesis of alkoxybromotriphenylenes: new discotic liquid crystals and valuable precursors to ‘mixed tail’ discotics

The phenolic moieties of hydroxyalkoxytriphenylenes are derivatized and reduced to yield alkoxytriphenylenes possessing reactive sites for aromatic substitution; simple bromination affords the first triphenylene discotic liquid crystal having only three alkoxy tails.

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...