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.