Packing Principles for Donor–Acceptor Oligomers from Analysis of Single Crystals

D–A conjugated molecules are complicated in both their molecular and their packing structures. In this perspective, we summarize more than 40 crystal lattices of conjugated oligomers to identify the morphological influence of each building block on the D–A molecules. These lattice structures reveal not only the packing preferences of the conjugated oligomers but also the conformational disorder in the lattices. The presence of this disorder in slowly grown crystals implies that attaining total long-range conformational order is challenging for D–A oligomers, which are structurally complicated and readily distorted and which have building blocks of incommensurate packing dimensions. In optoelectronic applications, a decreased duration of processing can prevent ordering and trap the thin films of D–A oligomers from becoming crystalline phases. Although D–A oligomers conform to packing principles in the formation of a single crystal, their phase behaviors in the formation of active thin films are much more difficult to comprehend. Continuous advances in methods of characterization are still strongly required for the steps of attaining a true structure–property relation of D–A oligomers in active films for optoelectronic applications.