Reversible on/off conformational switching of pentafluorobenzoyl amide triggered by acid vapor and sublimation

Most conformational molecular switches based on an amide skeleton are limited in their use in solution. We developed a molecular switch with an amide skeleton, which is applicable without a solvent. Treatment of solid 3 with HCl vapor (without dissolution) and sublimation switched the amide conformation by converting a dimethylamino group to a dimethylammonium group. The transformation was reversed by sublimation with pumping to remove HCl. This switching, which proceeds in the gas state in sublimation and not the solution state, was confirmed to be an on/off process by crystal analysis.