Study on helical structure of the B-4 phase formed from achiral banana-shaped molecule

The helical structure of the B-4 phase in the banana-shaped molecules, the 1,3-benzene bis[4-(4-n-alkoxyphenyliminomethyl) benzoate] (P-n-O-PIMB) seri es, has been studied by means of optical microscopy, X-ray diffraction and circular dichroism for homogeneously and homeotropically aligned cells. The homogeneously aligned cells showed a transparent blue color and a circular dichroism at about 400 nm, indicating the existence of a helical structure . Detailed texture observation also reveals the existence of two helical do mains with opposite helical senses. The two helical domains are formed with equal probability, and with the helical axes parallel to the layers simila r to the twist grain boundary (TGB) phase. This helical structure is also s upported by X-ray diffraction. The balance between the two domain areas is broken by doping P-n-O-PIMB with its chiral analogue. The texture of the ho meotropically aligned cells suggests two different helical axes, both of wh ich are parallel to the layer but with one parallel and the other perpendic ular to the bent-core plane.