Achieving switchable UV/Vis circularly polarized luminescence by varying excitation wavelength in chiral indium halides

Abstract

Chiral organic-inorganic hybrid metal halides (OIMHs) are promising for dynamic circularly polarized luminescence (CPL) in next-generation photonics. However, the dynamic switching of CPL signals across different emission regions, especially across the scarce ultraviolet (UV) region, remains a significant challenge. Herein, we report a pair of chiral indium halide enantiomers, (R/S-MPH₂)[In Cl₄(2,2′-bpy)]Cl (R/S-1, MP = 2-methylpiperazine, 2,2′-bpy = 2,2′-bipyridine), synthesized by leveraging the diverse coordination geometry of the In³⁺ ion and its balanced binding affinity for both halogens and organic ligands. Through the strategic incorporation of the UV-emissive 2,2′-bpy ligand and chiral blue-emissive (R/S-MPH₂)²⁺ cation, R/S-1 achieves reversible luminescence switching between the UV region (peaking at 345 nm) and visible (Vis) region (peaking at 460 nm). More importantly, effective chirality transfer, mediated through hydrogen bonding, enables CPL activity at these wavelengths with excitation-dependent characteristics. This system demonstrates the first reversible switching of CPL emission between the UV and visible regions in OIMHs. Notably, the CPL switching system also exhibits a large luminescence asymmetry factor (g_lum) in the UV region (∼10⁻¹), a value about 30-fold greater than that of the emission in the visible region. The practical potential of switchable circularly polarized light is demonstrated through the construction of a chiral photonic logic gate and a subsequent anti-counterfeiting system based on Morse code. This work offers a viable design strategy for dynamically tunable CPL materials while demonstrating the promise of such materials for advanced applications in information security.