Influence of spacer moiety and length of end chain for the phase stability in complementary, double hydrogen bonded liquid crystals, MA:nOBAs

Supra molecular liquid crystals formed by the Hydrogen Bonding interaction between a non-mesogenic aliphatic dicarboxylic acid viz., COOHCH₂COOH (Malonic Acid, MA); and mesogenic aromatic, N-(p-n-alkoxy benzoic)Acids, (i.e., nOBAs) for n = 3, 4, 5, 7, 8, 9, 10, 11 and 12, labeled as nOBA:COOH[CH₂]_mCOOH:nOBAs, abbreviated as MA:nOBAs are reported. ¹H NMR and ¹³C NMR studies confirm the formation of HBLC complexes. Infrared (IR) studies confirm the complementary, double, alternative type of HB. Polarized Optical Microscopy (POM) and Differential Scanning Calorimetry (DSC) studies infer N, SmC, SmX, SmC_RE, SmF, SmG LC phase variance. SmX phase exhibiting finger print texture grows in MA:nOBAs for n = 10, 11 and 12 by the interruption of SmC phase with decreasing temperature. Re-Entrant SmC (SmC_RE) grows by the cooling of SmX. I-N, N-C, X-C_RE, C-G, C_RE-F, F-G and G-Solid transitions exhibit first order nature. C-X is found to be second order nature in n = 10 and 11. C-X in n = 12 and X-C_RE and C_RE-F transitions are found to be weak first order nature. Influence of lengths of end chain (n) and spacer (m) for the overall LC phase [ΔT]_LC; tilted phase [ΔT]_Tilt; SmC phase [ΔT]_C and SmX phase [ΔT]_X stabilities is discussed in the wake of data on other HBLCs with similar molecular structure. Prevalence of SmX phase in MA:nOBAs with m = 1 infers repulsive interaction between the π-electronic cloud of aromatic boards of nOBAs. Model molecule predicts a twisted configuration of π-cloud around the molecular long axis. Finger print texture of SmX validates the model.