Improvements in the fatigue resistances of photochromic compounds

Whereas the majority of heterocyclic fulgides undergo extensive photooxidative degradations when used in naked spin-coated polymer films under the air, the degradations can be substantially depressed by a simple treatment: putting together a pair of the films on face-to-face and sealing with an adhesive to keep air-tight. By similar treatment, photodegradations of fulgimides in silica sol-gel matrices can also be substantially depressed, though fulgides undergo extensive hydrolysis. The method was less effective with some derivatives such as sulfur-containing fulgides, and little or nil effective with some spiropyrans, implying that some other degradation modes are dominant. The method provides a measure for the contribution of oxidative degradations by molecular oxygens, or else when the method is little effective it may imply some other degradation modes. The sealing treatment may also improve the thermal stabilities a little. (C) 2001 Elsevier Science B.V. All rights reserved.