Rapid and Reversible Visible-Light-Induced Helix Inversion in Chiral Liquid Crystals Doped with a Negative...

Light-induced helix inversion in chiral nematic liquid crystals (N*LCs), where helicity reverses under photoirradiation, has emerged as a promising strategy. However, existing systems often suffer from slow response times and limited reversibility, primarily due to inefficient photoisomerization. Here we report a binaphthyl-bridged imidazole dimer (BN-ImD) as a negative photochromic chiral dopant that enables rapid, visible-light-driven, and fully reversible helix inversion in N*LCs within seconds. BN-ImD undergoes efficient isomerization between a stable colored and metastable colorless form with a large dihedral angle change in the binaphthyl unit, while operating efficiently even in solid films and exhibiting fast thermal back reaction at room temperature. We also identified a second-stage, irreversible helix inversion triggered by protonation of the dopant under high-intensity irradiation, demonstrating a sequential helicity inversion that proceeds through two mechanistically distinct switching pathways of the chiral dopant. These findings highlight a new molecular design strategy for engineering multistage, light-controlled chirality in photoresponsive materials.