INTRODUCTION

Scientific community has done a lot of efforts for controlling molecular ordering of polymer chains through various supramolecular approaches. Among them, a famous approach is keeping the LC molecules a repeating unit of polymer chain. The self-assembling tendency of LC molecules tends to assemble polymer chains into well-ordered structures. A variety of liquid crystalline polymers (LCPs) have been synthesized since the discovery of LCPs in 1923 by Vorlander et al. to achieve the highly ordered polymers.1 The understanding of self-assembly in condensed phases is challenged by these polymers whose interpretation at a molecular level requires experimental investigations as well as the development of new molecular theories. However, the structural heterogeneity inherent in a polymeric system complicates these tasks. An alternative approach is the use of monodisperse low molar mass compounds whose behaviour encapsulates the essential physics of polymeric system for developing a molecular understanding of polymers.

Catalyzed with the motivation to understand LCPs at a molecular level, a wide variety of nonconventional low molar mass compounds were synthesized and shown to support liquid crystallinity. The fact that these compounds were LCs was very surprising because at that time most of the known low molar mass LCs were composed of molecules consisting of a single semirigid anisometric core with alkyl chains. Indeed, it had been widely assumed for many years that such a molecular structure was a prerequisite for the observation of liquid crystallinity. We now know that 1980s evidenced the beginning of the discovery of a rich diversity of structures capable of supporting mesogenic behaviour that has continued to the present day.

Of all these new low molar mass LC discovered during the 1980s, one class that attracted particular attention and which still remains the focus of much research are the so-called LC dimers. An LC dimer is composed of molecules containing two conventional mesogenic groups linked by a flexible spacer. Thus, LC dimers contravened the accepted structure–property relationships for low molar mass mesogens by consisting of molecules having a highly flexible core rather than a semirigid central unit. In this respect, LC dimers represent an inversion of the conventional molecular design for low molar mass mesogens. Several names have been used to refer to these materials including dimesogens or Siamese twins but these have all now been superseded by the preferred term LC dimer.