Photochromism of a new class of spiroindoline compounds

Photochromic processes of a new class of spiroindoline compounds (substituted 6-benzoyl-3,5-diaryl-spiro[cyclohexa-2,4-diene- 1,2'-indolines]) have been investigated by stationary irradiation and by laser flash photolysis. Ring-opening and ring-closure are reversible, but with repeated irradiation concentration of dye decreases. In laser flash photolysis experiments a strong solvent dependence was found. Ring-opening competes with intersystem crossing to T-1 and is the only reaction pathway in nonpolar solvents such as cyclohexane. Values of Phi .epsilon have been measured and are found to be strongly dependent on excitation wavelength for merocyanine formation.