Negative Photochromism of Asymmetric Binaphthyl-Bridged Imidazole Dimers

We report asymmetric binaphthyl-bridged imidazole dimers incorporating a dibenzoxepine moiety. Kinetic analyses of the photoisomerization process of the photo-switches reveal that the thermal back reaction of the colorless isomer proceeds through competing pathways to generate two structurally distinct isomers showing different color. These isomers undergo reversible isomerization via both photochemical and thermal processes, ultimately reaching a thermodynamic equilibrium. This work provides a practical molecular design strategy for controlling isomer distributions in photochromic imidazole dimer systems.