Negative photochromism in organic systems

The results of studies on negative photochromism of compounds and systems have been analyzed for the first time. It has been shown that the majority of studies deal with photochromic spiro compounds (spiropyrans and spirooxazines) whose negative photochromism is caused mainly by molecular structure, polarity and acidity of the medium, and complexation with metal ions. Among other most studied compounds, negative photochromism has been observed for photochromic dihydropyrenes. Photoisomerization of certain compounds, in particular, thioindigoid dyes, provides a photoinduced hypsochromic shift of absorption bands with substance color change.