Liquid crystal trimers containing tertiary benzanilide groups

Abstract

The rational design of new liquid crystal materials relies on an understanding of the relationship between molecular structure and the formation of liquid crystalline phases. The development of new materials can benefit from the use of a wide range of functional groups, but some groups prove challenging to combine with liquid crystallinity. Tertiary benzanilide groups are a clear example of this, as their strong conformational preferences disrupt liquid crystallinity when included in typical liquid crystalline structures. This means that it has not been possible to harness the molecular design possibilities offered by amide N-substitution. However, designing flexible structures to accommodate the conformation of tertiary benzanilides has allowed us to synthesise a variety of liquid crystal trimers forming nematic and smectic phases, and investigate the effect of lateral and N-substitution on their phase behaviour. Trimers with large (benzyl and decyl) N-substituents favour the formation of an orthogonal smectic (SmA) phase, and, unusually, exhibit pronounced negative thermal expansion.