Crystal structures and light absorption spectra of 1,4-dithioketo-3,6-diphenyl-pyrrolo-[3,4-c]-pyrrole

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Abstract
1,4-dithioketo-3,6-diphenyl-pyrrolo-[3,4-c]-pyrrole, which is a good charge generation material for a near-infrared electrophotographic photoreceptor, has three polymorphs called the I, II, and III forms. The I and II forms are transformed into the III form after having been kept in suitable organic solvents. On the other hand, the III form is changed to the I and/or II forms by heat treatment above 320 °C. Among the three polymorphs, only the highly ordered III form shows the necessary and characteristic absorption in the near-infrared region.