In this paper we present selected members of 7 new series of bent-shaped five-ring resorcinol derivatives which are distinguished by substituents at the central core as well as at the outer rings. Depending on the kind and position of the substituents and depending on the length of the terminal chains not only have new mesophases (the C PA phase or three unidentified B 2 -like phases) been identified, but also interesting phase sequences have been observed (B 2 -N; B 2 -SmA; B 2 -SmA-SmC; B 2 -SmA-SmC-N).

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New materials are presented, derived from the original banana compounds where the first smectic phases with polar switching (SmCP) were detected. Our results demonstrate that the introduction of lateral substituents on the central ring (F, Cl, CN, NO 2 , CH 3 ) and/or on the terminal rings (Cl, Br, CH 3 ) can significantly change the mesophase behaviour. The influence of such substituents is much more pronounced than in comparable calamitic compounds. The clearing temperatures are more or less depressed depending on the number, position and type of lateral substituents. In most cases the laterally substituted compounds form SmCP A phases. Of basic and theoretical interest are compounds where substituents (e.g. 4-cyano; 4,6-dichloro) on the central core enhance the bending angle giving rise to polymorphism variants with conventional smectic and nematic phases as well as ''banana phases'': N-SmCP A ; SmA-SmCP A ; SmA-SmC-SmCP A ; SmA-SmAP A -SmCP A . The last mentioned phase sequence has not been reported for single compounds up to now. Furthermore, the pool of materials allows us to compare the significant influence of lateral halogen atoms F, Cl, Br on the mesophase behaviour of bent-core mesogens for the first time. Nevertheless, up to now it has not been possible to predict the mesophase behaviour of bent core mesogens on the basis of the molecular architecture.

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New asymmetric four-ring bent-core compounds derived from N-benzoylpiperazine are presented. The mesophases were characterized by polarizing microscopy, DSC, X-ray diffraction, dielectric, electrooptical and SHG measurements. In some homologues the SmA as well as SmC phase can be transformed into a polar structure by applying an electric field. It was found for the first time that the polar SmI phase shows a ferroelectric switching which is obviously based on the collective rotation of the bent molecules around their long axes. It is remarkable that the ferroelectric structure is preserved on cooling into the solid state.

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