The influence of singlet oxygen in the fading of carbonless copy paper primary dyes on clays

Singlet oxygen was shown to be involved in the mechanism of fading on a clay surface of a series of the triphenylmethane (TPM) dyes used in commercial carbonless copying paper. The dyes adsorbed on clays were found to be singlet oxygen sensitisers and the singlet oxygen produced reacted with the dyes themselves. The rate of fading of a particular dye depended upon the structure of the dyes, fluorans degrading faster than phthalides.