Relationships between Mesophase Behavior and Crystal Structures of Chiral Smectogenic 4-[(S)-2-Methylbutyl]phenyl 4′-Alkoxybiphenyl-4-carboxylates

Interlayer distances of Sm*C and Sm A phases of the title series were measured as functions of temperature by X-ray diffraction. With increase in temperature, molecular tilt angles in Sm*C decrease from 22–25 to 0°. Crystal structures of the heptyl (1) and octyl (2) homologues have been determined by X-ray analysis. (1): 4-[(S)-2-Methylbutyl]phenyl 4′-heptyloxybiphenyl-4-carboxylate, monoclinic, P21, a=26.929(4), b=5.4249(5), c=9.2607(9) Å, β=96.78(1)°, Z=2. (2): 4-[(S)-2-Methylbutyl]phenyl 4′-octyloxybiphenyl-4-carboxylate, orthorhombic, P212121, a=9.249(1), b=56.259(9), c=5.412(1) Å, Z=4. Final R were 0.076 and 0.121, respectively. Both crystals have distinct layer structures similar to those of Sm*C. In the former crystal, the molecules tilt to one direction uniformly throughout layers, while in the latter, they take two opposite directions alternately from layer to layer. However, structures within a layer are very similar to each other. Each molecule has a coplanar biphenyl moiety and a twisted paraffin chain. Mesophase behavior was interpreted very well by the molecular interaction revealed in the crystal structures.