Perylene bisimide dimers of the type shown in the structure below could be synthesized in high yield and purity by condensation of the corresponding monoimide-monoanhydride with diamines. Dimers in which R and X were alkyl, aryl aralkyl and substituted groups were prepared and characterized by absorption and emission spectroscopy. Like the corresponding monomeric bisimides the extent of Π-overlap (manifested in the pigment color) in the solid dimers is dependent on the structure of the terminal R-groups but is even more sensitive to the nature of the X-bridging group. Most notably, xerographic electrical evaluation of model devices showed that dimers in which X was 1,3-propylene generally showed broader visible spectral response and higher photosensitivity than dimers with other bridging groups.
James M. Duff, C. Geoffrey Allen, Ah-Mee Hor, Sandra Gardner, "Synthesis, Spectroscopy and Photoconductivity of Dimeric Perylene Bisimide Pigments" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP15), 1999, pp 655 - 658, https://doi.org/10.2352/ISSN.2169-4451.1999.15.1.art00071_2