ABSTRACT
Spiropyrans (NIPS and BIPS), naphthopyrans or chromenes (CHR1) and spirooxazines (NOSI) in Scheme 1 have been extensively researched over the past five decades because of their properties of photochemical and thermal optical switchability. Their photochemical and thermal transformations from an ultraviolet (UV)-light-absorbing state to a visible-light-absorbing state can be harnessed for many practical applications [1-5]. Figure 1 shows a typical spectrum of a spiropyran in each of its two forms. These spectral changes result from a change in the extent of conjugation upon breaking or forming the sp3 carbon-oxygen bond in the ring-closed form of the molecule to switch to or from the ring-open meroform isomers as shown in Scheme 2. In the ring-closed form, the two ring systems are orthogonal and electronically independent, whereas in the mero-forms, the ring system’s -clouds are connected. Scheme 2 shows the photochemically and thermally inducible transformations of a typical example of each type of molecule.
