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 behaviours and photochromic properties which are desirable for optical switching. In this study, a novel compound 4c was synthesised by adding azo functional groups and chlorine substituent to the central bent-core. The structure, mesogenic properties, and photosensitivity of 4c was characterised by fourier-transform infrared spectroscopy (FTIR), 1H and 13C nuclear magnetic resonance (NMR), mass spectrometry (MS), differential scanning calorimetry (DSC), polarised optical microscopy (POM), and ultraviolet–visible spectroscopy (UV-Vis). The experimental results show that 4c exhibited a broad temperature window of nematic phase (63.8 °C), rapid trans – cis photoisomerisation in seconds, and high cis fraction of 0.81. At room temperature, 4c dissolved in ethyl acetate can reach photostationary state in 10 seconds. At 95 °C, nematic 4c became isotropic under UV irradiation in 3 seconds and can be restored to be nematic under natural visible light in 5 seconds. Quantum mechanics calculations confirm that using azos instead of esters as the central linkages can effectively reduce the molecular dipole moment and enhance the overall molecular polarisabilities, which promotes favourable mesogenic and photonic behaviours. This study provides novel synthesis route and synergistic approach to advance the design of azobenzene bent-core liquid crystals.