Phase behavior of some mono-substituted ferrocene- and [3]ferrocenophane-containing nematics with the cyclohexane ring in the rigid core

Generally, incorporation of the cyclohexane rings into the rigid core of rod-like mesogens leads to improved technological parameters, i.e. low viscosity, ambient transition temperatures and stability of the nematic state. Taking this into consideration, a series of novel cyclohexane-containing derivatives of ferrocene has been synthesized. The effect of various structural factors on liquid crystalline behavior of the synthesized ferrocene-containing nematics has been examined. Ferrocenophane compounds exhibited enhanced liquid crystalline properties in comparison with the derivatives of unbridged ferrocene. Depending on thermal prehistory of the samples, some of the synthesized ferrocenomesogens showed remarkable migration of the phase transition temperatures. In one case such behavior led to stabilization of the initially monotropic nematic mesophase in subsequent heating cycles. In another case, the phase transition shifts caused the lowering of the crystal-to-nematic transition temperature and the broadening of the mesophase range. There was also a case of alteration from the initially enantiotropic to monotropic behavior. The obtained novel metallomesogens are important footsteps toward the development of low-viscous and low-temperature materials for liquid crystal applications possessing a chromophoric, redox-switchable, polarizable and chemically stable superaromatic ferrocene unit.