Organobismuth Molecular Crystals for Organic Topological Insulators

Three different types of large and high-quality organobismuth molecular crystals were grown by a physical vapor transport process. The target organobismuth molecules that have similar molecular structures, except for the type and position of the functional group, were crystallized into colorless and wire-shaped crystals having lengths at the centimeter scale with uniform flat surface. The crystal-packing structures of the organobismuth crystals were determined by single-crystal X-ray diffraction. The results show that the molecular packing can be controlled by a slight change of the functional group due to their different intermolecular interactions. Especially, the Bi–Bi distance was successfully controlled to vary from 5.11(1) to 5.71(3) and 5.18(2) Å for triphenylbismuth (TPB), tri-p-tolylbismuthine (p-TTB), and tri-o-tolylbismuthine (o-TTB), respectively. The different crystal structures and Bi–Bi distances can affect the topological behavior of the materials. Moreover, the electrical and optical properties of the target organobismuth crystals were confirmed through the I–V characteristics, density functional theory calculation, and photoluminescence spectroscopy. These findings potentially offer a new route and strategy for the development of organic topological insulators.