Photosensitive elements based on polymeric matrices of diacetylenes and spiropyrans and the use thereof as coatings to prevent document reproduction

DETAILED DESCRIPTION These and other objectives are addressed by this invention with a photosensitive member fabricated by crosslinking diacetylene monomers utilizing spiropyrans as crosslinks and a photosensitizing dye.
The dye may enable the polydiacetylene to respond to radiations within the visible spectrum used for the reproduction of a document, thereby causing the spiropyrans to open into their colored form.
At substantially the same time, the spiropyran itself may absorb the ultraviolet part of the spectrum, also providing ring opening in its colored form.
The two concurrent actions may result in a deep coloration of the film, which substantially prevents the recording of the optical pattern representing the document.
Once the radiation ceases to exist, the spiropyran may return to its closed form and the film may revert to transparency.
The interaction of the diacetylene chains in the polymer with the spiropyran links may create conditions for selective response to a specific spectral distribution of the printing light as well as a given rise time of the light pulse.
These conditions can be adjusted by the length and composition of the link containing the spiropyran, thus creating various degrees of conjugation between the pi-orbitals of the spiropyran and of the monomer chains.
The introduction of a carbonyl group (See FIG.
6) in the link may provide a continuous intramolecular overlap of pi-orbitals extending from the spiropyran to the diacetylene chains.
Stabilized orbital delocalization corresponding to specific electronic states can be made to match a given spectral distribution in the printing light and allow the system to differentiate from ambient reading light.
Another element of differentiation is related to the kinetics of ring opening of the spiropyran in the presence of other active groups in the link itself or in the monomer chains.
Multistable states can relate to the rise time of the printing pulse.
In view of these considerations, crosslinked polymer structures which will respond specifically to the printing light while remaining unaffected by ambient reading light may be designed in accordance with this invention