Functional switching from circularly polarized luminescence to whispering gallery modes in a chiral Schiff base.

This work demonstrates a design concept for dual-mode optical materials, embodied by an axially chiral fluorescent Schiff base, (R/S)-BN-2HGCA. The compound exhibits two competing optical functions that are toggled by its physical aggregation state. In a dilute solution, the molecule's chirality is expressed, resulting in clear circularly polarized luminescence (CPL). In contrast, upon self-assembly into morphologically pristine microspheres, the chiroptical property is suppressed. This structural transition represents a functional transition where intense optical confinement within the microcavity is accompanied by suppression of the observable CPL, while enabling the emergence of whispering gallery mode (WGM) resonance. These spheres function as active optical resonators supporting distinct WGM resonance, with an average Q-factor of approximately 190, demonstrating effective light confinement within the self-assembled organic microcavities. Controlling dissolution and self-assembly to switch between chiroptical and photonic modalities provides a promising design concept that may be developed toward smart materials.