Novel optical anisotropy of a liquid crystalline “cubic” phase in a discotic crown ether derivative

To obtain a columnar structure with nucleophilic channels embedded in the column centres, we synthesized a series of new crown ether derivatives (compounds 1, 2, and 3) which are composed of a core of dibenzo-24-crown-8 symmetrically surrounded by four identical substituents. Experimental results indicate that compounds 2 and 3 with smaller substituents around the dibenzo-24-crown-8 core form only crystalline phases, while compound 1 bearing larger dendron substituents on the molecular periphery shows multiple liquid crystalline phase transitions. X-ray diffraction demonstrates that 1 can stack parallel to form a hexagonal columnar liquid crystalline (Colh) phase. A stable phase, which renders the diffraction features of a body-centred cubic (BCC) structure and shows unexpected optical anisotropy, is observed in between the Colh and the isotropic state. On the basis of further support from model calculations, we propose that the optically anisotropic “BCC” structure is an array of ellipsoidal domains placed in the BCC lattice with their long axis along the [111] direction, which results from the periodic density fluctuation of the columns.