Crystal and Molecular Structure of Electroactive Organic Materials under High Pressure

Research project P 14237 Crystal and Molecula Structure of Electroactive Organic Materials under High Pressure Roland RESEL 08.05.2000 Electroactive organic materials have high potential for future opto - electronic applications: e.g. as charge generation materials in laser printer or photocopy equipment, as light emitting diodes in flat panel displays or simply in "Plastic Solar Cells". Since the optical as well as the electrical properties of these molecular materials are highly anisotropic, the structural properties like crystal and molecular structure are of fundamental interest. The structural properties are determined mainly by the intermolecular interactions within the crystalline arrangement of the molecules. Pressure dependent studies of the crystal structure properties is one of the best methods to study the role of the intermolecular interactions and their role in the formation of the crystal structure. Pressure dependent investigations on molecular crystals of aromatic compounds will be performed by experimental and theoretical methods. The experimental methods are X-ray diffraction and Raman spectroscopy under pressures up to 60kbar. The theoretical methods are ab-initio band structure calculations. Both methods will support and extend each other: e.g. it will be possible to determine the changes of the unit cell size by X-ray diffraction experiments; however, the changes of the atomic coordinates of the molecule within the unit cell will be better accessible by a theoretical approach. The expected pressure induced phase transitions will be investigated also by theoretical and experimental methods. A detailed study of the pressure dependent structural properties of these electroactive organic materials should support the possibility to create designed molecular materials for special need in applications.