Molecular modeling studies of polymorphism in titanyl phthalocyanine

The morphology of phthalocyanine pigments used as charge generation materials can dramatically affect their photosensitivity. Titanyl phthalocyanine [O=Ti(pc)] is an example of this type of material, where the type IV polymorph possesses high photosensitivity (E-1/2<0.2 mu J/cm(2)) when formulated with appropriate charge transport materials. In this study, we have examined the known crystal structures (refined either from single-crystal or powder diffraction data) of titanyl phthalocyanine in detail, and have simulated their X-ray powder diffraction patterns for comparison with experimental data. Powder diffraction patterns have also been simulated for slight modifications of the crystal structures, with major effects observed for rotation of the molecule about the O=Ti axis and for variation in the crystallite size. Many so-called ''polymorphs'' claimed in the patent literature for the phthalocyanine pigments may well be ascribed to this type of subtle change in molecular geometry or crystal size.