Dimesogenic compounds with chiral tails: Synthesis and liquid crystalline properties of a homologous series of alpha,omega-bis[4-(4 '-(S)-(-)-2-methylbutoxycarbonyl-biphenyl-4-oxycarbonyl)phenoxy]alkanes

A series of new liquid crystalline dimesogenic compounds with chiral tails was synthesized, and their thermal and liquid crystalline properties were s tudied. The chain length of the central polymethylene spacers (x) was varie d from dimethylene (2) to decamethylene (12). These compounds were characte rized by elemental analysis, IR and NMR spectroscopy, differential scanning calorimetry (DSC), and cross-polarizing microscopy. All compounds were fou nd to be enantiotropically liquid crystalline, and the values of melting (T -m) and isotropization temperature (T-i) as well as enthalpy change (Delta H-i) and entropy change for isotropization (Delta S-i) decreased in a zig-z ag fashion revealing the so-called odd-even effect as x increases. Their me somorphic properties fall into three categories depending upon x; (a) compo unds with x=2 and 4 formed two different mesophases, smectic and cholesteri c phases in that order on heating, and vice versa on cooling, (b) compounds with x=3, 7, 8, 10 and 11 reversibly formed only the cholesteric phase, an d (c) compounds with x=5, 6, 9 and 12 exhibited only a cholesteric phase on heating, whereas on cooling they formed two different mesophases, choleste ric and smectic phases, sequentially.