Rubrene Polymorphs and Derivatives: The Effect of Chemical Modification on the Crystal Structure

Graphical tools based on Hirshfeld surfaces and two-dimensional fingerprint plots have been used to compare the different polymorphs of rubrene and the structures of rubrene substitution derivatives, deposited in the Cambridge Structural Database. Focusing on C center dot center dot center dot C contacts displayed both on the surfaces and on the fingerprint plots, some distinctive features related with the herringbone disposition of the molecules and their arrangement in pi-stacks have been observed. These features do not occur only for those rubrene molecules modified by the insertion of small functional groups but also in the case of bulky substituents. Although no particular trend was identified, this study should contribute to encourage the design of new improved rubrene derivatives that could exhibit the typical intermolecular contacts of orthorhombic rubrene, a feature that has been suggested to contribute to its excellent performance as a semiconducting material. As a consequence, the limited number of rubrene derivatives presently available should be increased, thus allowing a deeper analysis and a better understanding of the relationships between physical properties and crystal structures.