- Polydiacetylene (PDA) Langmuir films (LF) containing Zn2+ cations were prepared in different experimental procedures. The incorporation of zinc cations resulted in new morphological and spectral properties. We found that zinc cations stabilize the blue phase of PDA, and inhibit its transformation into the red phase, withstanding prolonged exposure to UV irradiation. The increased stability was accompanied with the loss of the linear strand morphology and appearance of a new, transient purple phase before the final red phase stage. It was found that the most significant differences in film properties occur when the zinc cations are already present in solution during the polymerization stage at sufficient concentration. In such case zinc ions penetrate into the headgroup interlayer in the trilayer organization, and are implicated in the film's chromatic properties. In cases where polymerization was carried out prior to introduction of the cations, the properties of PDA/Zn2+ films are similar to films produced on a pure water subphase.