Christian H. Erdelen

One-dimensional hopping transport in a columnar discotic liquid-crystalline glass

Abstract The charge carrier transport in liquid-crystalline triphenylenes is completely different from the transport in amorphous photoconductors. The high degree of order leads to quasi-one-dimensional transport. In this paper we are proposing a model for a field-assisted incoherent hopping process in one-dimensional systems based on Monte Carlo simulations. The numerically determined field and temperature dependences were compared with experimental results of a butyloxy-substituted triphenylene dimer. In this glass-forming material the mobility could be measured by a conventional time-of-flight technique in the very large temperature range between 128 and 410K. This dimer is, at room temperature, ordered in, a discotic hexagonal plastic phase with a very high hole mobility of 10−2cm2V−1 s−1. We have observed a transition from a non-activated to a thermally activated behaviour of the charge carrier mobility at –20°C, which we assign to a phase transition from the liquid-crystalline phase to the anisotrop...

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.

Triphenylenes: a new class of hole transporting material in organic light-emitting diodes

Electroluminescent devices consisting of triphenylene derivatives as hole transport layer (HTL) and 8- hydroxyquinoline aluminium complex (Alq3) as emitting layer with ITO as anode and aluminium as cathode are presented. Triphenylene compounds were evaporated or spin coated from solution. In addition side chain polymers with triphenylenes are used. Finally we prepared a polymeric HTL by photopolymerization of an acrylate functionalized triphenylene monomer. Some of the devices, based on ITO/Triphenylene/Alq3/Al showed brightness values up to 1000 cd/m2 and low turn on voltages from 4-5 V.

Columnar Mesomorphism of the Mixed Substituted Apolar Triphenylenes: Prognosis and Experimental Data

Abstract The calculations of molecular parameters (MP) of triphenylene derivatives with the mixed substituents were carried out here. The prognosis of columnar mesomorphism (CM) for this series of compounds was made on the basis of the value of MP. The compounds Ia-If are synthesized, their thermotropic and lyotropic mesomorphism have been studied. The good agreement of calculation and experimental data has been found for a new series of triphenylenes.