Synthesis, characterization, mesomorphic investigation, and DFT study of a symmetrical naphthalene-azomethine with terminal alkyloxy groups

A series of symmetric, rod-shaped molecules containing 1,5-di-amine-naphthalene as a central rigid core, with two phenyl rings attached to the terminal alkoxy chains, OCnH2n+2 (n = 5 –10), has been synthesized. The mesomorphic investigation indicates that all compounds generally exhibit an enantiotropic nematic phase. The rigidity and polarizability of the naphthalene unit result in a wide temperature N phase. Furthermore, an odd-even alternation was observed, showing that as the length of the terminal alkoxy chains increases, the temperatures of the crystal-nematic and nematic-isotropic phase transitions decrease. DFT studies revealed that the molecules adopt an all-trans conformation.