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.