Charge transport in crystalline organic semiconductors: using polymorphs to explore the effect of crystal packing

Organic semiconductors are a fascinating class of materials, with a wealth of properties and diverse technological potential. For small-molecule organic semiconductors, charge transport is closely related to the crystal packing motif. Polymorphism is frequently encountered in these materials, given the weak intermolecular interaction energies. This represents a unique opportunity to explore phenomena related to the fundamental mechanism of charge transport in organic semiconductors, such as the influence of the crystal packing. For example, 5,11-bis(triethylsilylethynyl)anthradithiophene has two polymorphs inter-convertible through phase transition that occurs at $T $= 294 K. We report on their crystal structure, formation, and the effect of the different molecular packing on the electronic properties. We discuss the technological implications that a room-temperature phase transition has on the performance and stability of devices fabricated with this material.