The effect of [n]-helicene length on crystal packing

Chiral $\pi$-conjugated organic molecules hold potential for emerging technologies as they are capable of introducing novel functionalities into electronic devices owing to their strong chiroptical properties. However, capitalizing on chiral molecules for electronic devices is reliant on their molecular packing—a factor that impacts their charge-transport properties. The solid-state behaviour of molecules is sensitive to subtle differences in molecular interactions, chirality, and shape, but these relationships are not fully understood. Here, we employ crystal structure prediction as a tool to probe the lattice-energy landscape for a family of chiral organic molecules: [$n$]helicenes, where $n$ ranges from 3 to 12. Our results show excellent agreement between the crystal structure prediction landscapes and experimentally reported structures. By analysing the packing motifs within the polymorph landscapes, we begin to develop an understanding of how helicene length affects the shape and $\pi-\pi$ stacking interactions seen in the polymorphs. Further, we propose how helicene length can be used as a tool to design new functional organic electronics.