Although amphiphilic TARC18 is achiral (Figure, left), it can form chiral Langmuir-Schaefer (LS) films upon organization of the molecules at the air/water interface. Moreover, the chirality of the film can be switched off and recovered by alternatively exposing the film to HCl gas and air (Figure, right; CD: circular dichroism). The process can be repeated more than ten times in the film state.