  In searching for novel photoactive liquid crystals, we have synthesized a
series of five-ring pyridine-based bent-core compounds bearing different
substituents at the peripheral phenyl rings (CH3O, Cl and NO2). Their
mesomorphic behaviour has been investigated by polarizing optical microscopy,
differential scanning calorimetry and X-ray scattering, and then compared with
the unsubstituted parent compound. The introduction of the methoxy groups at
the peripheral phenyl rings of the bent core results in a non-mesomorphic
compound, whereas the chloro- and nitro-substituted compounds form
enantiotropic B1-like phases. Significant changes of the textures and
transition temperatures of the mesophase have been observed under UV light. The
presented investigation of the mesomorphic properties of the synthesized
compounds, coupled with analysis of the molecular packing of the related
three-ring compounds, will help to design self-organized molecules suitable for
UV indicators.
