Distinct layered structure with density modulation in solid phase formed from B2 phase of banana molecules

A unique two-dimensional (2D) long-range structure has been observed in a low-temperature phase X1 for a banana molecule having bromine atom substituted on the central core using synchrotron radiation (SR) x-ray scattering measurements. The X1 phase is formed from the B2 phase with the Sm CA PA structure upon cooling and then shows multiple reflections around the first layer line, which are interpreted as a peculiar frustrated structure with long-range layer modulation order. Furthermore, the observation of a well-defined (100) reflection with a spacing of 171 means that there is the electron density modulation along the layers. By coupling these reflections, a 2D lattice with a=173 , c=53.4 , and β=81.1° is determined where the a axis is parallel to the original layer of the B2 phase. This unique structure with modulation can be interpreted as an undulated layer structure and suggested to be the result from deformation with polarization splay defects periodically occurring along the layer. The angle, β=81.1°, between a and c axes indicates that the position of splay defects in one layer is staggered from that in the neighboring layer. In other words, the splay defect lines run in a direction tilted by roughly 80° with respect to the a axis.