Study of the hydrogen bonding of 1,4-bis[(3,4,5-trihexyloxyphenyl)hydrazide]phenylene in crystalline and liquid crystalline phases using infrared, Raman, and two-dimensional correlation spectroscopy

The vibrational bands of a dihydrazide derivative, 1,4-bis[(3,4,5-trihexyloxyphenyl)hydrazide]phenylene (TC6), observed in the Raman and infrared spectra were assigned. The intermolecular hydrogen bonding vibrational bands due to CO and NH groups in the low-frequency Raman spectra were observed at 111 and 94 cm−1 in the crystalline and liquid crystalline (LC) phases, respectively. The sequential order of changes in the hydrogen bonding and alkyl chains was opposite in the crystalline and LC phases. The modifications in the hydrogen bonding occurred prior to conformational changes in the hydrocarbon chains in the crystalline phase; however, a reverse trend was observed in the LC phase. Simultaneously, the two-dimensional (2D) IR and Raman correlation spectroscopic analysis showed that the amide I band of TC6 in the LC phase comprised at least five distinct bands. In addition, the hetero 2D correlation between the NH and CO groups confirmed that no free NH and CO groups existed in the LC phase.