Absolute configuration and chiral self-assembly of rubrene on Bi(111)

We investigated the chiral self-assembly of rubrene molecules on a semi-metallic Bi(111) surface using low-temperature scanning tunneling microscopy. The absolute configuration of isolated rubrene enantiomers was identified from high-resolution images. Two types of homochiral domains of rubrene monomers and hexamers were observed, respectively. For rubrene monomers, chiral separation was spontaneous with each chiral monomer appearing in their respective domain. For rubrene hexamers, two levels of organization chirality were recorded: one is six heterochiral rubrene molecules arranged alternatively in a rubrene hexamer; and the other is a homochiral arrangement of individual hexamers. After annealing at 350 K, a large area of supramolecular self-assembled L- and R-type triangular heterochiral hexamers was obtained at the narrow terrace of Bi(111). Moreover, a molecular chiral inversion from the L-(R-) type to the R-(L-) type occurs during the formation of the hexamer domain structure and can be attributed to the enhanced intermolecular interactions governed by the intensive intermolecular extrusion at the narrow terrace.