Perylene pigments are known to exhibit a variety of shades in the solid state from vivid red, via maroon to black, although their solution spectra are quite similar. The color generation mechanism has therefore been investigated in three typical perylene derivatives on the basis of the crystal structure and intermolecular interactions. The color is found to be mostly determined by two absorption bands in the visible region: one is due to individual molecules and the other is caused by interactions between transition dipoles (“exciton coupling effects”). The red color appears as a result of insignificant exciton coupling while the colors of maroon and black are characterized by medium and strong exciton coupling, respectively.
K. Tojo, J. Mizuguchi, "Crystal and Electronic Structures of Perylene Derivatives" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP17), 2001, pp 564 - 567, https://doi.org/10.2352/ISSN.2169-4451.2001.17.1.art00029_2