Liquid Crystalline Mixtures with Induced Polymorphic Smectic Phases Targeted for Energy Investigations

Abstract

In this study, 4-Biphenyle-4′-alkyloxybenzenamines were synthesized as a homologous series of liquid crystals based on the biphenyl moiety. Their mesomorphic and optical properties were examined for both pure and mixed components. Elemental analysis, NMR, and FT-IR spectroscopy were used to determine the molecular structures of the developed materials. Using differential scanning calorimetry (DSC), the mesophase transitions were studied, and polarized optical microscopy was used to identify the textures of the mesophases (POM). The obtained results showed that all compounds are dimorphic and only have smectic B (SmB) and smectic A (SmA) phases for all terminal side chains, which are enantiotropic. With variably proportionated terminal side chains and a focus on the mesomorphic temperature range, binary phase diagrams were constructed and an induced smectic C phase was achieved (SmC). It was found that terminal chain length affects both conformation and steric impact in the mixed states. The absorption and fluorescence emission spectra of pure as well as their binary mixtures liquid crystalline films were recorded to investigate the optical and photophysical properties. It was noted that, with the increase in alkyl chain length, the energy bandgap increases from 3.24 eV (for C6H13) to 3.37 eV (for C16H33) and charge carrier lifetime decreases, ascribing to the increase in stearic hindrance causing, consequently, the faster decay of charge carriers.