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Abstract
Symmetrical four-chained (tetracatenar) di-hydrazine derivatives, namely oxalyl N',N'-bis(3,4-dialkoxybenzoyl)-hydrazide (BFH-n, n = 4, 6, 8, 10), were synthesised. Investigations on the liquid crystalline properties by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarising optical microscopy (POM) showed that the di-hydrazine derivatives exhibited columnar mesophases and the symmetry of the mesophase changes from rectangular to hexagonal on increasing the temperature. The rectangular columnar mesophases of BFH-n (n = 6, 8, 10) remained stable down to 10°C during cooling and the subsequent recrystallisation from the Colr phase of BFH-n (n = 6, 8, 10) was observed on the second heating runs. Furthermore, the average number of molecules packing in a column slice was estimated to be three, based on their X-ray diffraction results. Intermolecular hydrogen bonding between –C=O and −N−H groups in crystalline and liquid crystalline phases was confirmed.
Acknowledgements
The authors are grateful to the National Science Foundation Committee of China (project No. 50373016, 50873044), the Program for New Century Excellent Talents in the Universities of China Ministry of Education, Special Foundation for PhD Program in the Universities of China Ministry of Education (Project No. 20050183057) and Project 985-Automotive Engineering of Jilin University for their financial support of this work.