Spectrokinetic studies on new bi-photochromic molecules containing two naphthopyran entities

A range of new bi-photochromic molecules containing two identical (3a–d) or two distinct naphthopyran units (6a–d), linked through the phenyl substituents located on the sp3 hybridised pyran ring carbon atom, using conjugated and non-conjugated spacers, have been synthesised from bis-propynols and (substituted)naphthols. Study of the spectrokinetic properties of these compounds under near UV–vis continuous irradiation conditions revealed that the two naphthopyran units are stimulated independently leading to open forms with higher colourabilities but without affecting the individual bleaching kinetics. Compared to the individual photochromic components and to model mono-photochromes it was observed that the nature of the bridge has a small effect on the photochromic properties of each system