Aqueous Circularly Polarized Luminescence Induced by Homopolypeptide Self-Assembly

Remarkable advances have been achieved in solution self-assembly
of polypeptides from the perspective of nanostructures, mechanisms,
and applications. Despite the intrinsic chirality of polypeptides,
the promising generation of aqueous circularly polarized luminescence
(CPL) based on their self-assembly has been rarely reported due to
the weak fluorescence of most polypeptides and the indeterminate self-assembly
mechanism. Here, we propose a facile strategy for achieving aqueous
CPL based on the self-assembly of simple homopolypeptides modified
with a terminal group featuring both twisted intramolecular charge
transfer and aggregation-induced emission properties. A morphology-dependent
CPL can be observed under different self-assembly conditions by altering
the solvents. A nanotoroid-dispersed aqueous solution with detectable
CPL can be obtained by using tetrahydrofuran as a good solvent for
the self-assembly, which is attributed to the involvement of the terminal
group in the chiral environment formed by the homopolypeptide chains.
However, such a chiral packing mode cannot be realized in nanorods
self-assembled from dioxane, resulting in an inactive CPL phenomenon.
Furthermore, CPL signals can be greatly amplified by co-assembly of
homopolypeptides with the achiral small molecule derived from the
terminal group. This work not only provides a pathway to construct
aqueous CPL-active homopolypeptide nanomaterials but also reveals
a potential mechanism in the self-assembly for chiral production,
transfer, and amplification in polypeptide-based nanostructures.