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Chiral π-Conjugated Liquid Crystals: Impacts of Ethynyl Linker and Bilateral Symmetry on the Molecular Packing and Functions

Recently, various chiral aromatic compounds, including chiral π-conjugated liquid crystals, have been developed for their unique photofunctions. One of the typical photofunctions is the bulk photovoltaic effect of ferroelectric π-conjugated liquid crystals, which integrates a polar environment based on molecular chirality with an extended π-conjugation system. Tuning the spectral properties and molecular packing is essential for improving the optical functions of the chiral π-conjugated liquid crystals. Herein, we examined the effects of an ethynyl linker and bilateral symmetry on the liquid-crystalline (LC) properties and π-conjugated system through detailed characterization via polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction analysis. The spreading of the π-conjugated system was evaluated using UV–vis absorption and photoluminescence spectroscopy. Bilateral symmetry affects the LC and photoluminescent properties. Hetero-substitution with a sparse ethynyl linker likely allows the formation of an interdigitated smectic LC structure. Because the molecular packing and photophysical properties can affect the photo- and electrical functions, we believe this study can promote the molecular design of novel functional π-conjugated materials, such as chiral ferroelectric π-conjugated liquid crystals, exhibiting the bulk photovoltaic effect.