Heterocyclo-Annulated Spirooxazines and 2H-Caromenes: Two Complementary Series of Photochromic Compounds

Our purpose was to prepare heterocyclo-annulated spirooxazines and 2H-chromenes in order to extend the scale of the main photochromic properties (spectro-kinetical and photodegradation parameters) and to characterize the influence of the nature and positions of heteroatoms. - Nitrogenated six-ringed systems have very slight influence on kΔ, λmax and colorability of the photomerocyanines but an interesting power of enhancing the resistance to the fatigue. On the other hand the polyheteroatomic five-ringed systems present a broadening of the visible absorption spectrum but the photodegradation behaviour is not so satisfying. - The replacement of the indoline moiety by hindered azaheterocyclic systems has also an interesting effect on the visible absorption and (or) the thermal bleaching kinetics. - The accumulation of benzene nuclei and nitrogen atoms especially in the case of a 7-8 annulation on the spirobenzoxazine skeleton shifts the photochromic equilibrium toward a permanent merocyanine, the transoïd structure of which has been studied by X-Ray diffraction, 1H NMR and dipole moment. All these data are in agreement with a quinoïd or polyenic electron distribution. As a conclusion, the heterocyclic annulation is a good means for modulating the photochromic properties and can be coupled also to the effect of substitutents.