ELECTRON-TRANSFER COLORATION OF FLUORANE LEUCO DYES WITH IODONIUM SALT - AN APPROACH FOR COLOR STABILIZATION

A thermocoloration system consisting of a fluorane leuco dye (FR) and an iodonium salt (DPIOB) was investigated. The color for the FR/DPIOB system possesses a highly colored stability, The rates of the color de velopment reaction show a rapid rise with increase in temperature, and , owing to two kinds of different activation energy (E-a) at the range of reaction temperature in the polymeric film, the reaction easily oc curs in the high temperature region (>104 degrees C), The thermal susc eptibility increases with increase of FR/DPIOB content, A mechanism of thermocoloration via an electron transfer process is proposed. FR is oxidized to the FR+. radical, the iodonium cation is reduced to the di phenyl iodine radical, which then rapidly decomposes to iodobenzene an d the phenyl radical. The ring opened cationic ester (FR-Ph) is formed by radical coupling between FR+. and the phenyl radical. (C) 1998 Els evier Science Ltd.