Different forms of Nafion films were prepared and used to exchange phenothiazine and phenazine dye cations. The monomer dye molecules are emittive and the protonated and aggregated dye molecules are nonemittive. A spectrophotometer and spectrofluorometer were used effectively to identify these molecules in the adsorbed state and the control of different forms of dye molecules by Nafion film was clearly established. Protonation of the dye molecules occurred mainly in the proton-exchanged dry Nafion film (H+-Nf), whereas dimerization of dye molecules was predominant in the sodium-exchanged dry Nafion film (Na+-Nf). The higher acidity and narrow ionic cluster and interfacial regions of the dry Nafion films were found to control the protonation and dimerization of dye molecules. The dyes were predominantly in monomeric form in the wet H+- and Na+-Nf films. When the Na+-Nf film was in a wet condition, the ionic cluster and interfacial regions expanded to form a more open structure. When large hydrophobic organic cations like tetrabutyl ammonium ions (Bu4N+) and tetraethyl ammonium ions (Et4N+) were exchanged into the Nafion film, the film structure was totally controlled by these organic cations and, consequently, controlled the monomeric and dimeric forms of dyes in the film. The dye adsorbed dry H+- and Na+-Nf films may find applications in acid-base sensors.