The Interplay of Spacer Chirality and Parity in Mesogenic Dimers

A key fragment (S)-3-phenyl-3-hydroxypropanoic acid enables the synthesis of novel LC dimers with a chiral flexible spacer of different lengths. This work highlights the importance of the position of the chiral group within the dimeric molecule and demonstrates the complexity of chirality transfer from molecular to multiple levels of structural chirality.

Abstract

Introducing chirality into soft materials, including liquid crystals (LCs), profoundly impacts their self-organization and physical properties. In this study, we synthesized a novel series of LC dimers with a chiral center as part of their flexible spacer. The dimers were prepared in racemic and enantiomerically pure forms. Their spacer length and parity were varied to investigate the effect of spacer chirality and parity on mesomorphic behavior and on chiral induction in the nematic phase of achiral mesogens. Our results show that the even-membered chiral dimers only have chiral nematic phases. In contrast, the odd-membered dimers display rich mesomorphism, including the intriguing blue phase (BP) and chiral form of the twist-bend nematic phase (N*_TB). The observed significant difference in the 3D surface morphology between the racemic and chiral forms of the N*_TB phase suggests that the chiral moiety in the spacer promotes a chiral hierarchy. Furthermore, the chiral dimers show a prominent odd-even effect in the helical twisting power in nematic hosts. These findings highlight the importance of the position of the chiral group within the dimeric molecule and provide new insights into how intrinsic chirality in the spacer affects the overall structural chirality.

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