Cyano and Nitrobenzyloxy Derivatives: New Polymorphism Aspects

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 N_re → S_{G or H} with complex spatial structuring.

• The cyanobenzoate series provides examples of the so-called S_A1 A_Ad , S_A2 S_[Ctilde] phases and also an interesting S_Ad-S_A2 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 S_A I in a pure compound.

• The cyano-Schiff's base series presents the first example of a S_B hexatic phase in polar systems.

• The nitro-Shiff's base series not only exhibits a new enantiotropic re-entrant sequence K S_F S_c N_re S_A N I, but also the first example of the S_F phase in polar compounds and the inverted sequence K S_F S_c N S_A 1.