NEW-TYPE OF PHOTOCHROMISM IN THIOXANTHENE-10,10-DIOXIDE DERIVATIVES BASED ON THEIR PHOTORESPONSIVE ACIDITY CHANGE

3-Methoxycarbonyl-9-methyl-6-trans-phenylazo- and 3-cyano-9-methyl-6-t rans-phenylazothioxanthene- 10,10-dioxide were synthesized. They revea l a property as a carbon acid based on the proton dissociation at C(9) -H, and the dissociation constants are much larger in their trans-azo form than the tis form. Their conjugate bases possess absorption band at around 670 nm. Developing and bleaching of the color are linked wit h the trans - cis photoisomerization of the phenylazo group.