PHOTOCHROMISM OF A NEW CLASS OF SPIROINDOLINE COMPOUNDS

Photochromic processes of a new class of spiroindoline compounds (subs tituted 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 re peated irradiation concentration of dye decreases. In laser flash phot olysis experiments a strong solvent dependence was found. Ring-opening competes with intersystem crossing to T-1 and is the only reaction pa thway in nonpolar solvents such as cyclohexane. Values of Phi .epsilon have been measured and are found to be strongly dependent on excitati on wavelength for merocyanine formation.