Biomimetic Chiral Molecular Tweezers Based on Tryptophan-Containing Peptides with Chiroptical Evolution

Naturally occurring molecular tweezers in proteins are constituted by aromatic amino acids such as phenylamine and tryptophan, which include electron-deficient guests to form supramolecular complexes to achieve diverse functions. Inspired by the biomolecular tweezers, we introduce the tryptophan-based dipeptide system that performs as efficient chiral tweezers to include guests via charge-transfer interactions. In the solid and solution phases, the molecular tweezer bearing double indole entities undergoes folding though intramolecular CH···π bonds to afford a tweezer geometry. The tweezer hosts show structural universality, which could entrap a great variety of charge-transfer acceptors including synthesized and biomolecules such as vitamin K3. The inherent chirality of tryptophan allows for chirality evolution and transfer, whereby chiroptical evolutions are realized. Specific binding with acceptors such as 1,2,4,5-tetracyanobenzene induces the emergence of colorful luminescence at the visible region in a feasible control manner, which provides an alternative strategy to realize luminescence and circularly polarized luminescence from nonemissive peptides or proteins. The host–guest complexes self-assembled into helical nanoarchitectures, transferring chirality to the macroscopic scale. This work establishes a general protocol to fabricate biomimetic molecular tweezers with potential applications in luminescence and chiroptical materials.