Thermal and Electrooptical Properties of Ferroelectric Liquid Crystals Having OH Groups

Article abstract of DOI:10.1246/bcsj.64.1652

Four kinds of ferroelectric liquid crystals (FLCs) possessing OH groups, ((S)-2-methylbutyl 4-<4-(11-hydroxyundecyloxy)benzylideneamino>cinnamate 4a, (S)-2-methylbutyl 4-<4-(11-hydroxyundecyloxy)-2-hydroxybenzylideneamino>cinnamate 4b, (S)-2-hydroxypropyl 4-<4-(11-hydroxyundecyloxy)benzylideneamino>cinnamate 4c, and (S)-2-hydroxypropyl 4-<4-(11-hydroxyundecyloxy)-2-hydroxybenzylideneamino>cinnamate 4d) were prepared in order to understand how the introduction of OH groups in FLCs affect the phase behavior and electrooptical compounds 4a and 4b.Comparing 4b and 4d both of which have an OH group at the o-position of the benzylidene group with 4a dn 4c, the former samples show a higher S_A-isotropization (I) transition temperature than do the latter ones.It is suggested from IR spectroscopic results that inter- and intramolecular hydrogen bonding contribute to the stabilization of the S_A phase.The order of the helical pitch in the chiral smectic C (S_c*) phase was found to be 4b>4a>4d>4c within 1.8 - 6.6 μm.From an electrooptical effect due to a deformation of the helical structure in the S_c phase, the rise time of the surface director (τ_sr) and the rise time of the bulk director (τ_br) were measured to be as follows: τ_sr are 850, 1500, 30 and 70 μs, and τ_br are 12, 100, 0.17, and 0.35 ms for 4a, 4b, 4c, and 4d, respectively.It was found that the intramolecular hydrogen bonding results in a slower optical response time, whereas intermolecular hydrogen bonding results in a faster one.