Crystal Structure and Electronic Characterization of trans- and cis-Perinone Pigments

Perinones derivatives are industrially important pigments that exhibit shades in the solid state from red to bordeaux. Two representative derivatives are trans and cis isomers characterized by a clean reddish shade of orange (Pigment Orange 43) and bluish red (Pigment Red 194), respectively. The color generation mechanism has therefore been investigated in these compounds with special attention to the crystal structure and intermolecular interactions. The color in the solid state is determined by molecular absorption bands as well as additional bands at longer wavelengths due to excitonic interactions between transition dipoles. Especially, the molecule pairs along the stacking axis are found to play an important role in the determination of colors, giving rise to the clean orange of PO43 and bluish red of PR194.