Influence of chemical moieties and the flexible chain for the tilted smectic phases in linear hydrogen bonded liquid crystals with Schiff based pyridene derivatives

A novel series of hydrogen bonded liquid crystals (HBLC's) prepared from non-mesogenic 4-pyridine carboxaldehyde, p-n-tetradecyl aniline and mesogenic 4-n-alkoxy benzoic acids (nOBA's) are isolated by a condensation reaction followed by an HB complexation. Formation of HB complex and purity of product is confirmed by ¹H NMR and IR spectroscopic techniques. The phase variance exhibited by the present HBLC series of compounds viz., Py14BA:nOBA's (for n = 3-5, 7-9 and 12) is found to be AB in lower homologues and CF in higher homologues. Odd-even effect is exhibited by the series at I-SmA, I-SmC and LC to Solid transitions. Iso-SmA, Iso-SmC, SmA-SmB and SmC-SmF transitions are found to be of 1st order nature. The even higher homologues (for n = 8 and 12) exhibit a paramorphotic textural transition of 2nd order nature in their SmC phase. The influence of HB (soft-covalent) interaction and the inductomeric effect contributed by the end chains for the enhancement of transverse dipole moment μ _t, the stability of tilted LC phases (SmC and SmF) are discussed. An ACF Multi-Critical Point is predicted in the phase diagram for Py14BA:nOBA series of HBLC's in the vicinity of n = 5.