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

Self-assembly of bent-core mesogens into cybotactic N and interdigitated SmA phases. Self-assembly of bent-core mesogens into cybotactic nematic and interdigitated SmA phases. • The rarely encountered hockey-stick shaped 3,5-diphenyl-1,2,4-oxadiazole mesogens are synthesized and characterized. • The mesomorphism is induced through rational molecular design, which is scarcely reported for such materials. • Cybotactic nematic and interdigitated smectic ordering is confirmed by XRD studies with antiparallel association of mesogens. • DFT simulations confirmed the shape anisotropy, bend angle, dipole moment, energy band gap, and other molecular parameters. 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.