Ferroelectric behavior in metal-containing liquid crystals: A structure-activity study

Article abstract of DOI:10.1021/ja00084a033

The synthesis and physical characterization (thermotropic and ferroelectric behavior) of eight ortho-palladated dimers [Pd₂(μ-Cl)₂L*₂] is reported. They are derived from chiral imines HL* (HL* = p-R¹OC₆H₄CH=NC₆H₄-OR ²-p, with R¹, R², or both equal to (R)- or (S)-1-methylheptyl). The chiral imines, which contain one or two stereogenic centers, are not liquid crystals themselves. However, the dimeric complexes, which contain two or four stereogenic centers in their structure, exhibit both SmA and SmC* mesophases and enable the first comparative structure-activity study on metal-containing ferroelectric liquid crystals to be made. The ferroelectric properties obtained are better when there are chiral chains on the ortho-metalated aromatic rings, because the fixed conformation of these rings diminishes the chiral tail freedom, thus allowing a better coupling of molecular dipoles. The complexes with two chiral tails show important Ps_max values in the range 44-131 nC·cm^-2. The complex with four chiral chains (R¹ = R² = (R)-methylheptyl) is the first such compound ever reported containing four stereogenic centers; furthermore, it shows a remarkably high Ps_max value of 206 nC·cm^-2, the highest value reported so far for a metal-containing liquid crystal.