Thermotropic properties of ferrocene derivatives bearing a cholesteryl unit: structure–properties correlations

The synthesis and structural characterization of new liquid‐crystalline compounds containing ferrocene, azo‐aromatic and cholesteryl groups are reported. Taking into account the advantage brought by chirality, ferrocene and azo units, these structures could be good precursors for obtaining materials capable of responding to magnetic and electric fields or to UV‐light exposure. The influence of each structural unit (ferrocene, cholesterol, azo aromatic core and flexible chain length) has been studied by comparing analogous compounds possessing the same structure but without the element being analyzed. Ferrocene is a three‐dimensional bulky unit, so that, regardless of the substituents' nature, this unit could cause steric repulsions with neighboring molecules. These interactions could lead to a decrease of the transition temperature domain. Surprisingly, a decrease in the clearing point was not observed for the compounds discussed. This behavior was possible because ferrocene is connected to the mesogen via a flexible unit. As a consequence, both phenyl analogues and ferrocene derivatives presented liquid‐crystalline properties with similarly high clearing points, but above the thermal stability of derivatives with azo groups. Their melting points depend on the way the molecules are packed, with different crystalline states being detected in the case of ferrocene derivatives. In order to explain the liquid‐crystalline behavior of the compounds synthesized, molecular simulations were performed using the Hyperchem program. Copyright © 2005 John Wiley & Sons, Ltd.     

Monosubstituted ferrocene liquid crystals containing click triazole with a wide nematic phase temperature range

New monosubstituted ferrocenomesogens of the 1,4-substituted-1,2,3-triazole series 3a-3d and the 5-halogen-1,4-substituted-1,2,3-triazole series 4a-4d were successfully synthesised through a facile and versatile synthetic route using click reactions with moderate yields, in different atmospheres, and catalysed by different amounts of CuX (X = Br, I). Two series of compounds exhibited a typical nematic liquid crystal texture, and the 5-halogen-1,4-substituted-1,2,3-triazole series 4 had a wider mesomorphic temperature range than the corresponding series 3 due to the effect of the halogen atom substituent on the triazole. These compounds showed similar absorption spectra, but the fluorescence emission spectra of 4 were obviously redshift relative to 3. Cyclic voltammetry investigations revealed that the redox-active ferrocenyl groups of 3 and 4 follow one-electron transfer processes.     

Synthesis of ferrocene derivatives exhibiting low-temperature mesomorphism

Novel ferrocenomesogens exhibiting low-temperature mesomorphism have been synthesised from 4-ferrocenylphenol and n-alkoxy naphthoic acid intermediates (n = 4 to 16). The phase behaviour has been investigated in detail by polarising optical microscopy and differential scanning calorimetry.     

Monosubstituted thermotropic ferrocenomesogens: an overview 1976–1999

Research in the late 1940s in academic institutions, most notably the University of Hull in the UK, led to the development of liquid crystal display technology in the 1970s, which has subsequently had a large impact throughout the world. The liquid crystal technology is based on simple organic molecules. Since the late 1980s, some liquid crystal scientists have turned their attention to investigating the effect of introducing a metal atom into the systems. This review focuses on the major developments in the field of ferrocenyl‐containing liquid crystals in which the organometallic group is situated in a terminal position with respect to the core of the molecule. Metallomesogens with terminal metal atoms are not very common, since it can be deduced from the theory of organic liquid crystals that bulky terminal groups would not be conducive to the stabilization of liquid crystal phases. Nevertheless, a terminal ferrocenyl group can stabilize a nematic liquid crystal phase and examples of this will be discussed in this review. Copyright © 2001 John Wiley & Sons Ltd.     

The liquid crystalline properties of some ferrocene‐containing Schiff bases

The synthesis and characterization of new ferrocene‐containing mesomorphous compounds is described. In order to induce mesogenic behavior, the structure of the substituent was systematically modified. Derivatives with no more than two rings in the core did not exhibit liquid crystalline properties. The synthesized products were characterized using NMR, IR and mass spectroscopy, DSC and polarized optical microscopy. Copyright © 2007 John Wiley & Sons, Ltd.