Halogen Bonding to the Azulene Pi-System: Cocrystal Design of Pleochroism

We describe the rational development of a design to create pleochroic molecular solids, by using C-I...pi halogen bonds to pre-organise different types of chromophores in a cocrystal. Using as a blueprint the structure of a non-dichroic cocrystal of naphthalene, we show how the systematic introduction of chromophores able to act as halogen bond donors or acceptors enables the construction of optically interesting dichroic or pleochroic solids, demonstrating the reliability of C-I...pi halogen bonds in designing new properties.