Red or Near-Infrared Light Operating Negative Photochromism of a Binaphthyl-Bridged Imidazole Dimer

The development of red or near-infrared light (NIR) switchable photochromic molecules is required for an efficient utilization of sunlight and regulation of biological activities. While the photosensitization of photochromic molecules to red or NIR light has been achieved by a two-photon absorption process, the development of a molecule itself having sensitivity to red or NIR light has been now a challenging study. Herein, we developed an efficient molecular design for realizing red or NIR-light-responsive negative photochromism based on binaphthyl-bridged imidazole dimers. The introduction of electron-donating substituents shows the red shift of the absorption band at the visible-light region because of the contribution of a charge-transfer transition. Especially, the introduction of a di­(4-methoxyphenyl)­amino group (TPAOMe) and a perylenyl group largely shifts the absorption edge of the stable colored form to 900 nm. In addition, because the absorption band of one of the derivatives substituted with TPAOMe covers the whole visible-light region, the colored form shows a neutral gray color. Upon red (660 nm) or NIR-light (790 nm) irradiation, we observed the negative photochromic reaction from the stable colored form to the metastable colorless form. Therefore, the substituted binaphthyl-bridged imidazole dimers constitute the attractive photoswitches within a biological window.