S. Miki et al., NEW-TYPE OF PHOTOCHROMISM IN THIOXANTHENE-10,10-DIOXIDE DERIVATIVES BASED ON THEIR PHOTORESPONSIVE ACIDITY CHANGE, Chemistry Letters, (4), 1996, pp. 289-290
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.