Ferroelectric Behavior in Metal-Containing Liquid Crystals: A Structure-Activity Study

Abstract

The synthesis and physical characterization (thermotropic and ferroelectric behavior) of eight ortho-palladated dimers [Pd2(ji-C1)2L*2] is reported. They are derived from chiral imines HL* (HL* = />-R1OC6H,(CH=NQH4-OR* 12-p, with R1, R2, or both equal to (R)or (5)-l-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 Psmax 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 Psmax value of 206 nC-cnr2, the highest value reported so far for a metal-containing liquid crystal.

Synthesis and characterization of azo-linked Schiff bases and their nickel(II), copper(II), and zinc(II) complexes

“…Transition metal-complexed azo methine compounds have been studied in great detail in the literature for understanding their optical and electronic properties, structure-redox relationships, mesogenic characteristics [8][9][10][11][12]. Although many Schiff bases and their corresponding metal complexes have been extensively studied, relatively few water-soluble azo-linked Schiff bases and their metal complexes have been reported [13,14].…”

Synthesis, 2D NMR and X-ray diffraction studies on Cu(II) and Ni(II) complexes with ligands derived from azobenzene-cored Schiff base: Mesomorphic behaviors of Cu(II)–phenolates and crystal structure of bis[4-(4-alkoxy-2-hydroxybenzylideneamino)azobenzene]copper(II)

“…In view of the diversity of substituents thus introduced, a great variety of mesogenic complexes has been reported [12]. In this paper we report the preparation of new copper(II) and nickel (II) complexes derived from new bidentate Schiff bases.…”

Optically active, mesogenic lanthanide complexes: design, synthesis and characterisation

“…On the other hand, it has been well demonstrated that metallomesogens possessing molecular chirality can self-organise to form chiral phases such as the helical structures of the chiral nematic (N*) or chiral smectic C (SmC*) phases (1,2,(10)(11)(12). These features have potential in several applications.…”