Two-dimensional Infrared Correlation Spectroscopy Of Supramolecular Liquid Crystals Based On Hydrazide Derivatives

In recent years, LC materials have been widely investigated and great progresseshave been made. Three kinds of hydrazide derivatives including C16-NO2，TC6，E12-10-NO2are investigated using two-dimensional correlation analysis. Hydrogenbonding was confirmed to be the main driving force in those hydrazide derivativesand catagories of hydrogen bonding was also discussed in Smectic Phase.Conclusions are as follows by experimental analysis:As for C16-NO2,the ν(CH2) changes the trans conformation into the gaucheconformation before the phase transition from crystalline to smectic phase. In thephase transition process, the wavenumbers of stretching models of C=O and N-Hgroups shift largely, indicating the intermolecular HB is weakened and some evenbeing broken, and consequently the intermolecular distance was enlarged. And then,the skeleton of phenyl ring has enough space to change their conformation to weakenthe π-π stacking interaction. In the mesophase, the HB strength and the molecularconformation keep almost constant.As for TC6, the2D FT-IR correlation analysis revealed that the sequential orderof the changes in the hydrogen bonding and alkyl chains was opposite in thecrystalline and LC phases. The modifications in the hydrogen bonding occurred priorto the conformational changes in the hydrocarbon chains in the crystalline phase;however, the reverse trend was observed in the LC phase. Simultaneously, the2Dcorrelation spectroscopic analysis showed that the amide I band of TC6in the LC phase comprised at least four distinct bands at1685,1646,1633, and1618cm-1. Thesigns of the asynchronous cross peaks corresponding to these four bands indicatedthat the sequence of the spectral intensity change in the ascending order oftemperature was as follows:1685cm1>1633cm1>1618and1646cm1. The twobands at1618and1646cm-1might have resulted from the splitting of the broadamide I band at1633cm-1. Simultaneously, the aromatic ring skeleton stretchingvibration split into two bands at1589and1577cm-1. In addition, the hetero2Dcorrelation between the N-H and C=O groups exhibited no free N-H and C=O groupsin the LC phase; four species of hydrogen bondings existed between the N-H andC=O groups in the LC phase, i.e., the strong hydrogen bondings peaks at3259and1633cm-1, and the weak hydrogen bondings at3360and1633cm-1,3259and1685cm-1, and3360and1685cm-1.As for E12-10-NO2, at least four species of hydrogen bondings existed betweenthe N-H and C=O groups in the LC phase. At first, the modifications in the hydrogenbonding occurred inferior to the conformational changes in the hydrocarbon chains inthe crystalline phase as the temperature increasing.Second, at least five species ofhydrogen bondings existed between the N-H and C=O groups in the LC phase. thestrongest hydrogen bondings peaks at3206and1593cm-1, and the weak hydrogenbondings at3344and1593cm-1,3206and1649cm-1,3206and1656cm-1,3206and1681cm-1,3206and1695cm-1. It can be included that the intermolecular hydrogenbondings contribute a lot to the conformation of liquid crystalline of E12-10-NO2.