FATIGUE RESISTANCE OF PHOTOCHROMIC SPIRO-OXAZINES IN SOLUTION

The photodegradation of photochromic compounds, in spirooxazine series , has been investigated under continuous irradiation (Xenon lamp, 250 W) in toluene at 25 degrees C. The structure of the studied compounds was modified by various substitutions on the spirooxazine skeleton (he teroannellation on the benzoxazine nucleus or substitution of the indo line nucleus by an aza-bridged heterocyclic moiety). The photodegradat ion analysis of these compounds, as estimated by the parameter t(Ao/2) , allowed to determine the influence of the various structural modific ations on the fatigue resistance of the photochromes in solution. Thus , nitrogenated six-membered ring systems annellated on the benzoxazine moiety improve the fatigue resistance under W-visible irradiation con trarily to the five-membered systems. The replacement of the indoline nucleus by an azaheterocycloalcane system leads, to an interesting hyp sochromic shift on the lambda(max) of the coloured form but to a decre ase in the fatigue resistance of the compounds.