The electronic structure of C.I. Pigment Red 209

C.I. Pigment Red 209 (PR209) is a mixture of three kinds of isomeric dichloroquinacridones, 3,10-, 1,8-, and 1,10-derivatives. The colorant has attracted attention for its yellow shade of red, which is unusual for a quinacridone pigment. Elucidation of the pigment's crystal structure revealed that, of the three derivatives, only 3,10-DClQA was isolated as single crystals. X-ray analysis showed that 3,10-DClQA crystallizes in P 1− space group and that NH⋯O intermolecular hydrogen bonds in the [11−0] direction and which constitute a two-dimensional, hydrogen bond network. However, whilst 3,10-DClQA was found to lack the yellowish hue of PR209, the color can be attributed to 1,8- and 1,10-DClQAs which possess absorption bands at shorter wavelengths than 3,10-DClQA.