Abstract
Several polar molecules with three benzene rings and having the general formula:
have been synthesized. All these compounds are built with the flexible –CH;0– linkage and provide rather low temperature mesomorphic phases easily accessible for physical investigations.
The striking features of these six series are:
• The cyanobiphenyl series provides a rather classical polymorphism.
• The nitrobiphenyl series shows another example of the re-entrant nematic phase and furthermore a very spectacular transition Nre → SG or H with complex spatial structuring.
• The cyanobenzoate series provides examples of the so-called SA1 AAd , SA2 S[Ctilde] phases and also an interesting SAd-SA2 transition directly observable under the microscope.
• The nitrobenzoate series not only exhibits a classical re-entrant nematic phase, but also the inverted sequence K N SA I in a pure compound.
• The cyano-Schiff's base series presents the first example of a SB hexatic phase in polar systems.
• The nitro-Shiff's base series not only exhibits a new enantiotropic re-entrant sequence K SF Sc Nre SA N I, but also the first example of the SF phase in polar compounds and the inverted sequence K SF Sc N SA 1.