| 초록 |
Achiral 4-biphenyl carboxylic acid molecules (BPCA-Cn-PmOH) connected with phenol at meta-position by alkoxyl chains with various carbon numbers formed helical structures in the low ordered SmC and N phases. In order to understand the origin of helical structures, four other achiral 4-biphenyl carbonyl model compounds and a series of polyesters (BPEn, n=even) from BPCA-Cn-PmOH were studied using a combination of techniques. It is concluded that both the twisted conformation of the self-assembled head-to-head dimers and the phenyl groups at the end of the dimers are essential to form a stable helical structure. Furthermore, even though there are molecular bends in the polyester chains, helical structures do not form. Therefore, the origin of helical structures in these achiral molecules comes from the twisted conformation of head-to-head dimers, indicating that neither molecular chirality, nor molecular bends, nor molecular tilting is necessary to form helical structures. |
