Synthesis and self-organization of core-extended perylene tetracarboxdiimides with branched alkyl substituents

The influence of the core extension of perylene tetracarboxdiimides on the thermotropic behavior has been investigated. A homologous series of alkyl substituted tetracarboxdiimides, namely, perylene diimide, terrylene diimide, quaterrylene diimide, and coronene diimide, was synthesized. These compounds display absorption maxima in the region of 430-760 nm with high extinction coefficients and show a high thermal stability up to 450 degrees C. Structural evaluation revealed an identical columnar self-organization for the derivatives below their isotropization temperature. An intracolumnar packing of the disks with a lateral rotation of 45 degrees to each other resulted in a helical pitch containing four molecules. The phase transition to the isotropic phase is shifted to higher temperatures for larger aromatic cores within this series of compounds. On the other hand, differences in the self-assembly during crystallization from the isotropic phase were observed. While perylene tetracarboxdiimide and terrylene tetracarboxdiimide formed large and highly ordered domains with arranged edge-on molecules, the coronene tetracarboxdiimide disks self-organized face-on leading to a homeotropic phase. The different molecular orientation on surfaces was correlated with diversified substitution patterns of the aromatic cores. The manipulation of the molecular architecture opens thus the opportunity to control the spontaneous self-alignment. This improvement of the macroscopic organization ensures an undisturbed percolation pathway for charge carriers between electrodes in field-effect transistors or in photovoltaic cells.