Rewritable color recording media consisting of leuco dye and biphenyl developer with a long alkyl chain

Media formulated using two compounds (a leuco dye and 4-alkoxyl-4′-hydroxybiphenyl) were colored in the amorphous state and colorless in the crystalline state. As the alkyl chain length of the biphenyl compound increased, the contrast ratio and thermal stability of the amorphous states increased. Additionally, the crystallization velocity increased for the media with a long alkyl chain. Leuco dyes with a high glass transition temperature also produced thermally stable amorphous states. The origin of the long alkyl chain effects is discussed.