Dyes as guests in ordered systems: current understanding and future directions

The optical properties of dyes dissolved in liquid crystals have led to their proposed use in a diverse range of practical applications. Such guest–host systems are typically required to fulfil a range of criteria relating to their absorption properties, degree of alignment and stability, but concurrently satisfying these requirements has proven a barrier to their widespread use. In this article, many of the proposed applications and their requirements are discussed, and an outline of some of the most prevalent classes of dye proposed in the context of guest–host systems is given, along with a summary of recent reports of dyes that exhibit thermotropic mesophases. Theoretical approaches to describing the alignment within guest–host systems are outlined, and possible strategies for the future rational design of guest–host systems are discussed.