Switchable columnar metallomesogens.: New helical self-assembling systems

Chiral oxovanadium(IV), copper(II), and palladium(II) beta-diketonates show a room-temperature columnar mesophase which undergoes ferroelectric switching. All the compounds were obtained as liquid crystals at room temperature, and crystallization or melting processes were not detected by differential scanning calorimetry carried out to -20 degrees C. The mesophase was investigated by optical microscopy, DSC and X-ray diffraction, and identified as a rectangular columnar (P2(1)). The flowerlike texture observed for all the compounds led us to deduce a high tilt angle (ca-40 degrees) of the molecules with respect to the column axis. Circular dichroism has confirmed the existence of a helical arrangement within the column. This result is in accordance with the so-called columnar mode found at low frequencies (ca. 10(-3) Hz) in dielectric spectroscopy studies. The electrooptical response of these materials has been examined by means of a photomultiplier. The results obtained can be explained by considering a strong influence of the high tilt angle found in the mesophase.