UV-vis spectra of PSPE solutions and films (with and without PSPE) were measured using an Optizen Pop UV-vis spectrophotometer (Mecasys, Seoul, Korea). The spectra of PSPE solutions and pH indicator films with PSPE, in pH values of 2.0–10.0, were measured in the range of 400–700 nm after the pH values of PSPE solutions were adjusted by adding 0.1 M HCl and NaOH to the desired pH value and the indicator films were immersed in each pH buffer. The spectra of PSPE and pH indicator films (with and without PSPE), after exposure to pH 6.0 buffer solution, were measured in the range of 300–600 nm to confirm the incorporation of PSPE into the pH indicator film.