The Origin of Helical Suprastructure from Achiral 4-Biphenyl Carboxylic Acid Molecules

A novel series of achiral 4-biphenyl carboxylic acid molecules (BPCA-Cn-PmOH) connected with phenol at meta-position by alkoxyl chains with various carbon numbers (n = 6-10) formed spontaneous helical suprastructures in the low ordered SmC phase. In order to understand the origin of phase chirality without configurational chirality in BPCA-Cn-PmOH, four other achiral 4-biphenyl carbonyl model compounds with an alkoxyl chain (n = 6) 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 suprastructure, but the -OH or -OCH3 functions at the meta- or para-position of phenyl ring is not necessary.