Research Articles The use of Diarylethene Derivatives for Photo-switching | TCI

The process of reversible coloration changes induced at least in one-direction by photoirradiation is referred to as photochromism.1) The two isomers of photochromic compounds differ in their geometrical and electrical structures. These geometrical and electrical differences lead to changes in the physical properties of the molecules, such as their absorption and fluorescence spectra, refractive index and electrical conductivity. Since the transformation between the isomers is induced by photoirradiation, optical-switching of the physical properties can be realized by using the photochromic units. Diarylethene, which contains f ive-membered heterocyclic rings, is well known as a photochromic compound that is thermo-irreversible, has high-sensitivity and has fatigue resistance properties.2) Photochromic reactions in diarylethene take place between two isomers, (hexatriene and cyclohexadiene) following the Woodward-Hoffmann rule (Figure 1). The open-ring isomer, hexatriene 1a, is generally colorless, but the closed-ring, cyclohexadiene isomer 1b, develops yellow, red and blue coloration, depending on the substituents.