The recent progress on the methods to prepare donor (D)–acceptor (A) co-crystals and their potential applications in OFETs has been reviewed.

Binary charge-transfer complex polymorphs composed of perylene and 4,8-bis­(dicyanomethylene)-4,8-dihydrobenzo-[1,2-b:4,5-b′]-dithiophene (DTTCNQ) were synthesized separately via a simple artificial nucleation-tailoring method, in both macroscopic and microscopic cocrystal engineering manners. The two polymorphs were testified to be independently thermosalient in the solid state, and the specific self-assembly derived from homogeneous or heterogeneous nucleation by assistance of governable thermodynamic/kinetic drive, leading to a change in the ordered p–n stacking structure. The as-prepared polymorphic microcrystals afforded a significantly varied (opto)­electronic property: high n-type transporting and good photoresponsivity for β-complex, and ambipolar transporting with ignorable photoresponsivity for α-complex, attributing to the different charge-transfer and supramolecular alignment. This work provides us a new route to the exploitation of donor–acceptor complex family, making it possible to develop functional materials and devices based on variable supramolecular binary structures.

A feasible strategy relies on using heteroatom replacement, namely, chemical modification of an organic compound. Here we present this design concept for donor−acceptor complexes, which involves introducing nitrogen atoms to the middle ring of donor molecules to promote short contacts and reduce steric effect of the mixed framework. These nitrogen-modified complexes can possess a shorter molecular distance besides the mixed-stacking pathway, enlarged π−π interactions, or even a scarce 1:2.5 molar ratio through extra acceptor insertion. As a result, the unique 1:2 complex with nitrogen atoms on the different sides demonstrated stable electron field-effect mobility performance, whereas the binary system with no nitrogen replacement or N atoms on the identical sides displayed poor ambipolar properties. These results confirmed that heteroatom replacement was a powerful molecular design tool to fine-tune the molecular packing of organic donor−acceptor complexes and their corresponding electronic properties.

A new crystal phase of a naphthalenediimide derivative (α-DPNDI) has been prepared via a facial polymer-assisted method. The stacking pattern of DPNDI can be tailored from the known one-dimensional (1D) ribbon (β phase) to a novel two-dimensional (2D) plate (α phase) through the assistance from polymers. We believe that the presence of polymers during crystal growth is likely to weaken the direct π-π interactions and favor side-to-side C-H-π contacts. Furthermore, β phase architecture shows electron mobility higher than that of the α phase in the single-crystal-based OFET. Theoretical calculations not only confirm that β-DPNDI has an electron transport performance better than that of the α phase but also indicate that the α phase crystal displays 2D transport while the β phase possesses 1D transport. Our results clearly suggest that polymer-assisted crystal engineering should be a promising approach to alter the electronic properties of organic semiconductors.