| abstract |
Compounds of formula I or III or mixtures thereof ##STR1## wherein R is unsubstituted C 6 -C 14 aryl or C 6 -C 14 aryl which is substituted by C 1 -C 12 alkyl, C 1 -C 12 alkoxy, C 1 -C 12 alkylthio, phenyl, benzyl, --CN, --CF 3 , halogen or --COOR 3 , x is 1 or 2, and R 1 is H, linear or branched C 1 -C 12 alkyl, C 2 -C 12 alkenyl or C 2 -C 12 alkynyl, C 7 -C 16 aralkyl, C 8 -C 16 alkaralkyl, --CH 2 COOR 3 or C 1 -C 12 acyl, wherein R 3 is H, C 1 -C 18 alkyl, cyclohexyl, cyclopentyl, phenyl, C 1 -C 12 alkylphenyl, benzyl or C 1 -C 12 alkylbenzyl, are reversible photochromic systems which can be used for contrast formation, light absorption or for the reversible optical storage of information. |