Hydrogen bond liquid crystal complexes (HBLCs) are successfully isolated from the mesogenic compounds of 4-n-alkyloxybenzoic acid (nOBA, n = 10 and 11), and the non-mesogenic compound of 1,3‑phenylenediacetic acid. Formation of H-bonds between the mesogen and non-mesogen and the presence of functional groups are detailed using FTIR analysis, whereas, UV–Vis spectroscopic analysis endorses the nature of the electronic transition and optical properties of the HBLC complexes. Polarizing optical microscopy (POM) textural analysis authenticates the presence of induced mesophases along with transition temperatures. Mesophase transition temperatures and changes in enthalpy, entropy of the resultant mesogens is assessed by differential scanning calorimetry (DSC) studies. It is noticed that the formation of H-bonds induces rich phase polymorphism with an extended mesogenic range. Furthermore, the thermodynamic equilibrium of the HBLC system is confirmed by the enthalpy calculation, which shows that the amount of energy absorbed by the system is equal to the amount of energy released by the system. Another interesting observation is that the thermochromic phenomenon exhibited in the nematic phase offers valuable insights for diverse sensor applications. The repeated thermal scanning and positive entropy values favour the thermally stable mesogenic HBLCs. Moreover, the obtained result elucidates the critical role of hydrogen bonding and molecular ordering in governing the mesomorphic behavior of the synthesized HBLC complex.
Valarmathi et al. (2026) studied this question.