Synthesis of 4-Chloro-1,3-Diazobenzene Bent-Cores Liquid Crystal and Characterizations of Its Mesogenic Behaviors and Photosensitivity

Azobenzene-based bent-core liquid crystals demonstrate a variety of mesomorphic behaviors and photochromic properties which are desirable for optical switching. In this study, a novel compound was synthesized by adding azo functional groups and chlorine substituent to the central bent-cores to form a 4-chloro-1,3-dizaophenylene bent-core. This compound was characterized by fourier-transform infrared spectroscopy (FTIR), ¹H and ¹³C nuclear magnetic resonance (NMR), mass spectrometry (MS), differential scanning calorimetry (DSC), polarized optical microscopy (POM), ultraviolet–visible spectroscopy (UV-Vis) to evaluate its structure, mesogenic properties, and photosensitivity. The experimental results show that compound 4c exhibits a broad temperature window of 63.8 °C for nematic phase, rapid photoisomerization in seconds, and high cis fraction 0.81. At room temperature, compound 4c dissolved in ethyl acetate solution can reach photostationary state in 10 seconds. At 95 °C, compound 4c in nematic phase became isotropic liquid under UV-irradiation in 3 seconds due to the forward trans – cis photoisomerization and can be restored to be nematic under natural visible light in 5 seconds because of the backward cis – trans photoisomerization. Density functional theory calculations confirm that the diazo as the central linkages instead of esters can effectively reduce the molecular dipole moment, which promotes these favorable characteristics. This study provides valuable insights to improve future design of azobenzene bent-core liquid crystals for practical applications especially in photonic applications.