Synthesis and Properties of Mesogens Containing Chiral Terminal Substituent with Hydroxy Group

Abstract
The synthesis of the chiral 4-[(S)-2-methyl-3-hydroxypropyloxy]-4'-formylazobenzene (S-MHPFAB), 4-[(S)-2-methyl-3-hydroxypropyloxy]-4'-cyanoazoxybenzene (S-MHPCAOB) and 4-[(S)-2-methyl-3-hydroxypropyloxy]-4'-cyanobiphenyl (S-MHPCB) is described. The chemical structures of compounds obtained were characterized by elemental analysis and proton nuclear magnetic resonance spectrometry. The mesomorphic properties have been investigated by polarizing optical microscopy. It is found that the formylazobenzene and cyanoazoxybenzene containing chiral terminal substituent with hydroxyl group possessed no liquid crystalline properties. Cyanobiphenyl S-MHPCB formed a nematic phase on cooling. Optically active cyanobiphenyl S-MHPCB induced a chiral nematic phase in the mesophase of the supramolecular liquid crystalline 4-(3-hydroxypropyloxy)-4'-cyanobiphenyl with a characteristic «finger print» texture and large value of the pitch of the cholesteric structure. The dielectric constant as a function of temperature has been determined via dielcometry measurements, and the dielectric anisotropy of the studied cyanobiphenyl S-MHPCB and system 4-(3-hydroxypropyloxy)-4'-cyanobiphenyl (90 %) – S-MHPCB (10 %) were revealed. It was found that the cyanobiphenyl S-MHPCB exhibited a small negative dielectric anisotropy and the studied mixture exhibited a small positive dielectric anisotropy. The effects of the molecule structure on the mesomorphic and dielectric properties of compounds obtained and their mixtures have been studied and discussed.

Keywords: synthesis, chiral terminal substituent, NMR-spectroscopy, phase transition temperatures, dielectric anisotropy