Banana-shaped Mesogens: Odd-even Effect in Dimeric Twins

摘要

The synthesis, characterization, and mesomorphic properties of a series of homologue compounds 1 derived from salicylaldehydes are reported. These compounds were characterized by ~1H, ~(13)C-NMR spec-troscopy and elemental analysis. The phase behavior of these mesogenic compounds was characterized and studied by differential scanning calorimeter (DSC) and polarization optical microscope. All compounds 1 were found to be mesogenic, and the mesophases were dependent of the carbon length of the spacer group. The results indicated that all compounds with an even-carbon spacer (m = 2, 4, 6, 8) exhibited smectic C phases; however, all other compounds with an odd-spacer (m = 3, 5, 7) formed banana phases. The difference in phase behavior was attributed to the dependence of the molecular shape and/or geometry on the parity of the central spacer when considered in the all-trans-conformation. The formation of the mesophases was related to the optimized conformation of the compounds. The most stable optimized geometry was also simulated by the semi-empirical Spartan '04 version 1.0.0/AM1 method.