Interdigitated orthogonal smectic and cybotactic nematic mesomorphism in three-ring hockey-stick-shaped 1,2,4-oxadiazole mesogens

Although hockey-stick-shaped liquid crystals with three-ring molecular architecture show remarkable thermal behavior, work on such systems is rarely reported. In particular, the investigations incorporating the novel oxadiazole core, which provides thermal and hydrolytic stability as well as polarity, have been scarcely presented. Given these observations, we intended to investigate such LCs derived from 3,5-diphenyl-1,2,4-oxadiazole. In this study, we report on the synthesis and elaborative characterization of a novel series of hockey-stick-shaped mesogens namely, methyl 4-(5-(4-n-alkoxyphenyl)-1,2,4-oxadiazol-3-yl)benzoate. To reveal the structure-property correlations, the substitution on the C-3 core in the form of methyl ester group has been held constant, while the substituent on the C-5 core has been varied with different n-alkoxy tails. While the thermal gravimetric analysis confirms the thermal stability, the methodical studies on the mesomorphism using optical, calorimetric, and X-ray diffraction techniques confirmed the occurrence of smectic A and nematic phases having interdigitated and cybotactic orders respectively. The lower and middle/higher members, respectively, show the N phase, and N and SmA phases, which follow the general trend reported hitherto for the homologues series of LC compounds. The quantum mechanical calculations using density functional theory revealed the bending angles, dipole moments, and HUMO/LUMO band gaps.