Homoatomic paramagnetic sulfur radical anions as colored species in ultramarines

EPR investigation shows that in ultramarine green, ultramarine blue, ultramarine violet and ultramarine red, paramagnetic polysulfide (-1) radical anions exist such as are also found in solutions of polysulfides in electron pair donor (EPD) solvents. In ultramarines, the following sulfur radical anions are observed: sup(.)S-, sup(.)S2- (yellow), sup(.)S3- (blue) and sup(.)S4- (red). They are also the colored species in the above ultramarines. (author)