Abstract
Recent studies on chromotropism such as photochromism, thermochromism, piezochromism, and electrochromism of organic compounds are described. Main topics are as follows :
1. Development of heterocyclic fulgids which are thermally stable photochromic compounds free from photochemical side reactions, and suited for use in information storages.
2. Finding of photochromism and thermochromism of viologens by an electron-transfer reduction-oxidation mechanism, similar to that of electrochromism of viologen family.
3. Survey of piezochromic materials which exhibit change of color on grinding, or pressing and revert to origingl color on heating or exposed to the vapor of organic solvents.
