Chiral Alanine Functionalized Perylene Diimides: Supramolecular Self-Assembly and Optical Properties

Water-soluble alanine-functionalized perylene diimide derivatives (PDI-Ala) were synthesized by introducing alanine units at the imide positions of the PDI framework. Their photoluminescence properties and supramolecular aggregation behavior were investigated in solvents of varying polarity. Chiral L-PDI-Ala displayed distinct solvent-dependent emission colors and intensities, whereas the achiral PDI-Ala showed negligible emission under the same conditions. Poor solvents such as acetone and ethyl acetate promoted relatively efficient emission with hypsochromically shifted bands, while good solvents such as N, N-dimethylformamide and dimethyl sulfoxide induced bathochromically shifted emission with much lower quantum yields. The results indicate that strong face-to-face π-π stacking in the solid-state leads to aggregation-caused quenching (ACQ), whereas ordered aggregates formed by intermolecular forces such as hydrogen bonds or stacking in solution can recover luminescence. On the basis of the spectroscopic and structural results, a solvent-regulated emission mechanism involving excimer/exciplex formation together with H-type and J-type aggregation is proposed. This work provides useful insight into the aggregation-controlled optical behavior of chiral amino-acid-modified PDI materials and offers guidance for the design of chiroptical and self-assembled luminescent systems.