| 摘要 |
A photosensitive layer comprises (a) at least one heterocyclic photochromic spiropyrane which can exist in a closed or open structure, the closed structure being converted to the open structure on irradiation with ultra-violet light, and the open structure being reconverted to the closed structure on irradiation with visible light, (b) at least one ortho-substituted nitrogen-containing thioether, and (c) at least one reagent capable of developing a latent image produced in the layer. In use of the layer, it is exposed to ultra-violet or visible light, and after exposure the layer is heated to cause conversion of the thioether to a thione at those areas of the layer in which spiropyrane in the open form is present: the spiropyrane in the open form catalyzing the conversion of thioether to thione and thereby amplifying the latent image produced on irradiation of the layer. The thione produced then reacts with the developing reagent to form a visible image.
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