Seeding Control in Chirality Triggering of Red-Emitting Organic Charge-Transfer Cocrystal Helixes from Achiral Molecules

Supramolecular chirality has gained immense attention for great potential, in which the rational engineering strategy facilitates unique helical stacking/assembly, high chiroptical behavior, and prime biomedical activity. In this study, we reported a novel chiral organic donor–acceptor cocrystal based on asymmetrical components of benzo(b)naphtho(1,2-d)thiophene (BNT) and 9-oxo-9H-indeno(1,2-b)pyrazine-2,3-dicarbonitrile (DCAF) that exhibited red emission using a simple solution approach. During the self-assembly, a kinetically controlled growth of polar solvent or substrate induction led to the chiral packing and helical morphology twisted by the cooperation of electrostatic potential energy and chirality. Intriguingly, a "seeding-control" mechanism was newly developed for the production of c-BNT–DCAF helical crystals with a defined uniform chiral form, which enables chirality transfer and amplification from the microscopic to macroscopic level via supramolecular stacking. By introducing chiral additives or even a small break at the edge, the first nucleus acted as a chiral seeding to guide the donor/acceptor molecule alignment into the same handedness. A remarkably high dissymmetry factor (glum) value of 0.1 was demonstrated on the chiral manipulated ribbons, which is the highest among the reported charge-transfer complexes. This work offers us more paths for the design of chiral supramolecular systems for vital applications in organic optoelectronics, micro/nanomechanics, and biomimetics.