Metallomesogens polarisability

Refractive index studies allow measurements of the birefringence, but also of the polarisability. The mean polarisability (a) can be determined using an isotropic liquid solution, whereas the polarisability anisotropy (Aa) is measured in the mesophase. Polarisability studies have been made on palladium, platinum, iridium and silver metallomesogens, and show a higher polarisability for the metal complexes than for their parent ligands. ... 

The number of studies on luminescence of metallomesogens in the liquid crystal state is still limited, but considerable progress is to be expected in the near future. New strategies for the design of room-temperature mesophases exhibited by metal complexes will make more types of metallomesogens available for photophysical studies. The possibility to obtain polarised emission via these systems and the use of these compounds in luminescent devices can be an additional drive for further exploration of this research field. ° The most promising metal ions to be included in luminescent metallomesogens are Eu, Tb, Sm, Ru, ... 

Calamitic metallomesogens forming a chiral smectic C phase (SmC ) are ferroelectric materials. Due to the low symmetry of this phase when the helix is unwound (C2) the molecular dipoles are aUgned within the layers of the SmC phase, giving rise to ferroelectric order in the layers. Because the SmC phase has a helical structure, there is no net macroscopic dipole moment for the bulk phase. However, it is possible to unwind the helix by application of an external electric field or by surface anchoring in thin cells. Under such conditions, a well-aligned film of the ferroelectric liquid crystal can exhibit a net polarisation, called the spontaneous polarisation (Ps). Ferroelectric liquid crystals are of interest for display applications because the macroscopic polarisation can be switched very fast by an... 

Spontaneous polarisation can also be observed for chiral discotic metallomesogens forming columnar mesophases, when the chiral molecules are tilted with respect to the column axis. The tilt induces a dipole moment within the plane of the molecule. A net macroscopic polarisation can be obtained for rectangular columnar phases with Cz or P2i symmetry. Serrano and Sierra reported on ferroelectric switching in the columnar mesophase for chiral /3-diketonate complexes (Figure 2.52). ... 

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