Elastic Properties of Dichloro- and Dibromoanthracene Crystals

The elastic properties of organic semiconducting crystals have attracted much attention in terms of the creation of nanomechanical devices. Dichloroanthracene (Cl2An) and dibromoanthracene (Br2An) derivatives, which form plate-like single-crystals, change the morphology of the one-dimensional (1D) column structure of anthracene and its intermolecular interaction depending on the substitution position of Cl or Br atoms. If uniform two-dimensional (2D) shear planes exist in the crystals, then the application of external stress is expected to allow elastic deformation of the crystals. However, the elastic behavior varied, depending on the morphology of the 1D column structure. Elastic behavior of the crystals was not observed when the long-axis of anthracene molecules in the π-stack tilted at 45° to each other (9,10-αCl2An) and when a permanent dipole moment existed at the perpendicular to the column (1,8-Br2An). Depending on the 1D column arrangement, elastic deformation may occur in two planes of the crystal (in the width W and height H directions of the platelet single-crystal) or only in one plane (in the height H direction). This can be distinguished by whether the 1D column arrangement is uniform and forms a uniform 2D-shear plane, or whether the columns are arranged in a zigzag manner, forming a 2D plane.