Design and Synthesis of Novel Organic Mesogens: Exploring Structure–Property Relationships in Liquid Crystalline Phases

Abstract

Background: A liquid crystalline mesogen is an organic compound that has both fluidity and some degree of long-range molecular organization, making the molecules useful in optics, display devices, and photonic applications. The mesophase behavior of these molecules is very sensitive to molecular structure and even minor structural changes have large consequences in terms of thermal properties, optical properties and supramolecular structure.

Aim: This research seeks to design, synthesize, and characterize a new array of organic mesogens in order to define clear structure-property relationships and define the molecular characteristics that control mesophase type, transition temperature, and functional response.

Method: A series of mesogens that included biphenyl and Schiff base, benzothiadiazole, triphenylene, and cyanostilbene core functionalization were prepared by the strategy of esterification and condensation. Affirmation of the structures was performed by FTIR, NMR, and HRMS spectroscopies. The mesophase behavior was investigated by polarized optical microscopy (POM), Eulerian differential scanning calorimetry (DSC), and X-ray diffraction (XRD) measurements, whereas dielectric and second harmonic generation (SHG) measurements conducted dielectric spectroscopy and second harmonic generation (SHG) experiments.

Results: The synthesized mesogens showed a variety of mesophase behavior with nematic, smectic and columnar phases obtained. The introduction of polar groups like NO 2 and CN increased PH stability and dielectric anisotropy and discotic cores induced columnar orientation. Optical measurements indicated great birefringence and large SHG results, especially with the Schiff base and triphenylene structures. Molecular frameworks were solid with thermal stability across the series being greater than 290 o C.

Conclusion: The results show that by systematic molecular design, the mesophase behavior and functional properties can be accurately controlled and this provides avenues to inventing next-generation liquid crystalline materials in photonic and electro-optical applications.