ABSTRACT
Photochromic compounds change their structures by photoirradiation. Change in color is one of the accompanying properties with the photochromic structural change. Usually one isomer is colorless and thermally more stable than the colored counterpart. The main class of photochromic compounds that shows change in chirality by photochromic transformation is that based on electrocyclization. Photochromic reactions of cis-1,2-diarylethenes are the extension of photochemical electrocyclization of cis-stilbene, which yields dihydrophenanthrene. Organic photochromic compounds have been used for the autoregulation of ophthalmic plastic lenses and for little else. But chiral photochromic compounds hold more information than nonchiral or racemic photochromic compounds, so they have a great advantage over them. In general, if a photochromic compound has an intrinsic chirality that is preserved during the photochromic reaction, it is just an extension of photochromism of achiral molecules unless the intrinsic chirality does not induce the generation of the second chirality in the biased ratio.
