Mechanistic Study on Gold-Like Luster Development of Solution-Cast Oligo(3-methoxythiophene) Film

Solution-cast coating films of perchlorate-doped oligo(3-methoxythiophene) exhibited a gold-like luster similar to that metallic gold despite the involvement no metals. However, development mechanism remains ambiguous. To understand mechanism, we performed scanning electron microscopic analysis, variable-angle spectral reflectance measurements, and ellipsometry measurements on ClO4−-doped cast film with luster. The results revealed lustrous color was not induced by submicron-sized regular structures (structural color), nor high-density free electrons (reflective response based Drude model), but large optical constants (refractive index extinction coefficient) film, as speculated previously.