Banana-shaped molecular architecture: Formation of large columns composed of two concentrically enclosed layers

Abstract

The room-temperature solid phase (X3) of banana-shaped molecules that forms on cooling from the B6 phase is characterized as having an extremely large hexagonal lattice. In this study, we acquired a detailed structure of the X3 phase from synchrotron radiation (SR) micro-beam X-ray and atomic force microscopy (AFM) measurements. Focusing the micro X-ray beam on a single fan-shaped domain, we observed a well-oriented pattern including nine hk0 reflections with spacings of 20–110 A. These can be indexed with a two-dimensional (2-D) hexagonal lattice with an edge length of 126.8 A and incorporating approximately 70 molecules. The hk0 reflections appear in a direction parallel to the long axis of the fan-shaped domain showing that the two-dimensional lattice exists in a plane perpendicular to both the layer and bent direction of the molecules in the preceding B6 phase. An AFM image clearly illustrates the close packing of cylinders with a diameter equal to the hexagonal lattice edge. Further, the electron density map elucidated from the X-ray reflection intensity distribution shows that each cylinder is constructed of two concentrically enclosed layers.