Novel five-ring bent-core compounds exhibiting a transition from the electro-optically nonswitchable to a switchable B7 phase

Two homologous series of achiral five-ring bent-core compounds derived from 2-cyano- or 2-nitroresorcinol having terminal n-alkyl carboxylate groups have been synthesized and characterized. All the compounds investigated show enantiotropic mesophases. Interestingly, the compounds derived from 2-cyanoresorcinol display two mesophases and the higher temperature mesophase shows unusual electro-optical characteristics. In contrast, the nitro-substituted compounds exhibit only one mesophase, which switches electro-optically. This mesophase and the higher temperature phase exhibited by the cyano-substituted compounds show similar characteristics and have been shown to be the same. These observations are unusual but very interesting and represent the first example of a transition from the electro-optically nonswitchable B-7X phase to a switchable B-7FE phase.