Cyano and Nitrobenzyloxy Derivatives: New Polymorphism Aspects

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.