Alignment structure formed in dimeric liquid crystal molecules

An antiferroelectric liquid crystal (AFLC) with dimeric molecules which take a bent molecular structure may show the nematic (N) phase. However, it has not been obvious yet why the antiferroelectric chiral SmC (SmC*A) and N phases may coexist in the phase sequences of the dimeric AFLC. In this study, the molecular alignment structure of both liquid-crystalline phases has been researched in detail with a polarized Fourier transform infrared spectroscopy (FT-IR). In 8PY11OCB, the directors of both mesogenic moieties are oriented to the rubbing direction due to high thermal motion in the N and SmA phases, that is the molecular shape is almost rod like. In the SmC_A phase, a herringbone alignment of the mesogenic moieties appears because the bent molecular structure becomes stable due to lower thermal motion. In the case of OBnCB, we obtain also almost the same results and discussion.