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 μt, 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.