Chiral Transcription on Achiral Carbon Dots by Linking with Chiral Histidine for pH‐Tunable Dual‐Mode Chiroptical Switch in Circular Dichroism and Circularly Polarized Luminescence

Carbon dots (CDs) have garnered significant attention for developing stimuli-responsive chiroptical nanomaterials. However, CDs featuring simultaneously reversible electronic circular dichroism (ECD) and intrinsic circularly polarized luminescence (CPL) have not yet been reported. Herein, we developed a novel kind of dual-mode chiroptical switches based on achiral CDs through post-modification with L-/D-histidine (L-/D-His). Through a mild amidation reaction, L-/D-His is not only covalently linked to the surface of CDs, but also closely attached to the luminescent centers via non-covalent hydrogen-bonding and π-π interactions, which facilitate efficient chiral transfer from L-/D-His to the luminescent centers of the CDs. Consequently, the chiral His-modified achiral CDs (L-/D-His-CDs) exhibit attractive chiroptical properties with both elegant ECD and intrinsic CPL across the entire visible spectrum. Intriguingly, the ECD and CPL signals of L-/D-His-CDs can be reversibly switched to those of their enantiomers by alternating pH values between neutral and basic conditions. Our results indicate that the pH-modulated protonation and deprotonation of imidazole directly modulate the surface non-covalent interactions, triggering chiral conformational inversion and thereby enabling reversible ECD and CPL signals. This study establishes a facile strategy for the construction of stimuli-responsive chiroptical switches from achiral CDs by rational chiral ligand modifications.