Structural comparison of two bisphenol S derivatives used as colour developers in high-performance thermal paper

Abstract The crystal structure of a new bisphenol S derivative, 3,3′-diallyl-4,4′-dihydroxydiphenyl sulfone was analyzed. This compound is used as colour developer in high-performance thermal paper, because of its high colour sensitivity and excellent image stability. In the crystalline phase, each molecule of this derivative is linked to four neighbouring molecules by O H⋯O S intermolecular hydrogen bonds. In order to understand the solid-state properties of the new derivative, its hydrogen bonding features were compared to those of the parent bisphenol S compound. The hydrogen bonding network of the new derivative forms two-dimensional square lattice sheets stacked along the b axis. This stacking arrangement, which is different from that of the unsubstituted compound, results in a lower number of hydrogen bonds per unit volume. This structural feature was considered to be correlated with the considerably lower melting point of the new derivative compared to that of the unsubstituted one. This property would result in a good coloration sensitivity of the new derivative when used as colour developer.