Time-Dependent Solid-State Polymorphism of a Series of Donor–Acceptor Dyads

In order to exploit the use of favorable electrostatic interactions between aromatic units in directing the assembly of donor–acceptor (D–A) dyads, the present work examines the ability of conjugated aromatic D–A dyads with symmetric side chains to exhibit solid-state polymorphism as a function of time during the solid formation process. Four such dyads were synthesized, and their packing in the solid state from either slower (10–20 days) or faster (1–2 days) evaporation from solvent was investigated using single crystal X-ray analysis and powder X-ray diffraction. Two of the dyads exhibited tail-to-tail (A–A) packing upon slower evaporation from solvent and head-to-tail (D–A) packing upon faster evaporation from solvent. A combination of single-crystal analysis and XRD patterns were used to create models, wherein a packing model for the other two dyads is proposed. Our findings suggest that while side chain interactions in asymmetric aromatic dyads can play an important role in enforcing segregated D–A dyad assembly, slowly evaporating symmetrically substituted aromatic dyads allows for favorable electrostatic interactions between the aromatic moieties to facilitate the organization of the dyads in the solid state.