Aromatic Heterocycles Used as Terminal Groups of Calamitic Liquid Crystals

Abstract

Three series of compounds 1-21 were prepared by using 2-, 3-, and 4-pyridinemethanol as terminal group of calamitic liquid crystals. These compounds have some similarities in their phase behavior. They all exhibit SmA phase. A tilt smectic phase, SmC, will be formed when their flexible alkoxy chain is longer than hexoxy group. The profound difference between them is that the compounds 15-17 possess a short temperature range of N phase. The compounds 3 and 6 have the widest SmA phase, up to 94°C, and SmC phase, up to 46°C, respectively. . fore, three series of compounds 1-21 were derived from 2-, 3-, and 4-pyridinemethanol and their mesogenic properties were studied. The synthesis and structures of these compounds are shown in Fig. 1. RESULTS AND DISCUSSIONThree series of compounds 1~21 were prepared by the esterification of seven analogous aromatic carboxylic acids and 2-pyridinemethanol, 3-pyridinemethanol, or 4-pyridinemethanol. Their structures were identified by IR, 1 H-NMR, 13 C-NMR, and MS. The spillting pattern and chemical shift of H-atom positioned ortho to hetero N-atom of pyridyl ring will give enough evidence to differentiate these three pyridyl ring system. The liquid crystal phases and phase transition temperatures of 1~21 were determined by DSC measurement and texture observation. These data

Tuning the mesogenic properties of 5-alkoxy-2-(4-alkoxyphenyl)pyrimidine liquid crystals: the effect of a phenoxy end-group in two sterically equivalent series

“…[4] The use of aromatic end-groups in the rational design of new smectic liquid crystals may hold significant potential because non-covalent arene-arene interactions can be finely tuned by aromatic substitution, [23][24][25][26] although there are only a few reports of areneterminated mesogens in the literature. [27][28][29][30][31][32][33] The first reports by Gray et al focused on homologous series of phenyl-terminated alkyl 4-(benzylideneamino)cinnamates (e.g. 1) and revealed alternations in the nematicisotropic transition temperature (T NI ) and entropy of transition with increasing length and parity of the phenyl-terminated alkyl chain that are significantly more pronounced than those normally observed in the absence of a phenyl end-group.…”

Mesomorphic Behaviour and DFT Insight of Arylidene Schiff Base Liquid Crystals and Their Pyridine Impact Investigation

“…The terminal heterocyclic ring has a reasonable impact on the dipole moment. Therefore, the position of the nitrogen atom in the rod-like LC also influences the mesophase stability [36]. In rod-like LCs containing pyridine in their rigid core, compounds possessing pyridine may also serve as charge-transfer donors in binary systems (based on the position of the pyridine ring) [37].…”