Competitive induction of circularly polarized luminescence of CdSe/ZnS quantum dots in a nucleotide–amino acid hydrogel

The design and fabrication of chiral inorganic materials with circularly polarized luminescence (CPL) have attracted great interest. Herein, achiral fluorescent quantum dots (QDs) were found to show CPL activity upon doping into the two-component hydrogels composed of N-[(9H-fluoren-9-ylmethoxy) carbonyl]-glutamic acid (Fmoc-Glu) and deoxyguanosine (dG). It was found that the helical structures could be formed in the two-component hydrogels, and the helicity was dependent on the absolute configuration of Fmoc-Glu. Upon introduction of water-soluble achiral CdSe/ZnS QDs into the hydrogel, the hydrogel could transmit chirality to QDs and make achiral QDs show obvious CPL signals. The mirrored CPL spectra of QDs were obtained when the enantiomeric Fmoc-Glu was used, i.e., negative and positive CPL signals appeared in the L-Fmoc-Glu/dG and D-Fmoc-Glu/dG hydrogels, respectively, which indicated that the CPL signal followed the molecular chirality of Fmoc-Glu. However, when K+ ions were added into the co-assembly of Fmoc-Glu/dG/QDs, only negative CPL signals of QDs could be obtained regardless of whether the L-Fmoc-Glu or D-Fmoc-Glu was used. It was suggested that the G-quadruplex (G4) was formed when K+ ions were introduced into the gel, which is more competitive in inducing the supramolecular chirality of achiral QDs than Fmoc-Glu. This study provides not only a convenient way to fabricate CPL-active QDs via gelation, but also a deep understanding on the competitive chirality transfer in the multi-component supramolecular hybrid system.