Chirality transfer from atropisomeric chiral inducers to nematic and smectic liquid crystals - synthesis and characterization of di- and tetra-substituted axially chiral binaphthyl derivatives

Abstract

The chirality transfer of axially chiral binaphthyl derivatives bearing liquid crystal (LC) moieties at the n,n' positions (n 3, 4, 6) of the binaphthyl rings to nematic (N) and smectic (S) LCs is investigated. Chiral nematic LCs (N*-LCs) are prepared by adding a small amount of the chiral binaphthyl derivative into host N-LCs composed of cyanobiphenyl mesogen cores. The binaphthyl derivative with phenylcyclohexyl (PCH) type LC moieties at the 4,4' positions of the binaphthyl ring [D-4,4'] exhibits a low helical twisting power (HTP) of 11 mu m(-1). In contrast, those with LC moieties at the 3,3' and 6,6' positions of the binaphthyl rings [D-3,3' and D-6,6'] exhibit high HTPs of 153 mu m(-1) and 154 mu m(-1), respectively. Next, the binaphthyl derivatives are added into two types of S-LCs with phenylbenzoate mesogen cores: 4-(4-methylpentyloxy) phenyl-4-(decyloxy) benzoate [PhB1] and 4-(3-methylpentyloxy) phenyl-4-(decyloxy) benzoate [PhB2]. The mixture of the host LC, PhB1 or PhB2 with the chiral dopant, D-3,3' or D-6,6' shows chiral smectic LCs C (S-C*-LCs). The highly twisted S-C* phases with helical pitches of 1.2-1.4 mu m are prepared in PhB1 and PhB2 by using the chiral dopant of D-6,6'. It is concluded that D-6,6' has a large helical twisting power and is the most favourable atropisomeric chiral inducer for chirality transfer to both N-LCs and S-LCs.