Improving the stability of photochromic fluorinated indolylfulgides

Fluorinated indolylfulgides are a class of photochromic organic compounds. It is possible to consider potential applications of these compounds in optical devices such as switches and memory. Two novel fulgides, a deuterated trifluoromethyl indolylfulgide and a trifluoromethyl dicyclopropyl indolylfulgide, were designed based on prior mechanistic studies to have greater thermal stability and potentially greater photochemical stability. The absorption spectra, thermal stabilities in both toluene and polymer films, and photochemical fatigue resistances of both fulgides were measured. The cyclizable Z-form of the dicyclopropyl fulgide displayed a significant red shift of the absorption maximum compared to any other fulgide. Deuteration led to greater thermal stability of the fluorinated fulgide. Moreover, the Z-form of the dicyclopropyl fulgide showed excellent durability in PMMA at 80 °C. The solution-based study of the dicyclopropyl fulgide demonstrated only E–Z-isomerization after prolonged treatment (380 h) at 80 °C in toluene. In addition, the trifluoromethyl dicyclopropyl indolylfulgide is the most photochemically stable yet reported; it underwent 10,000 photochemical cycles, coloration followed by bleaching, before degrading by 13%.