Visualization of Polyaniline Polaron Red with Sunset Effect

The red color reflection from a polyaniline emeraldine salt (PANI-ES) in a vessel at an oblique angle was evaluated. The PANI-ES reflects green and red light in the normal direction, but only red light in the oblique direction, due to the characteristic refractive index of the polaron red color. This phenomenon is referred to as the "polaron sunset effect". Observing the PANI-ES from an oblique angle enables the polaron color to be visualized.