Reversible multi-coloring reaction of spironaphtooxazine controlled by long-chain molecule

A novel reversible multi-colored (red, violet, blue and yellow) film was realized using a typical photochromic dye (the color former) and docosylphosphonic acid (the color developer). A mixture of the color former/color developer exhibiting reversible multi-coloring reactions was controlled by heat-treatment of the solid phase. The structure and crystalline state of the film mixtures were investigated by UV–vis spectroscopy, X-ray diffraction and high-resolution electron diffraction measurements. The color of the films was controlled by the structural type of the photomerocyanine-form (protonated zwitterionic, zwitterionic and quinoid). The mechanism of the multi-coloring reaction was concluded to be the chemical combination of color formers and color developers, which produces red and violet colors, and when the coloration-temperature acts to separate the color formers from the color developers, yellow color appears. Furthermore, the color of the film changed from yellow to blue upon 360 nm light irradiation.