Design and synthesis of near-infrared absorbing pigments. II. Structure determination of aceanthrene green and derivatives

The reported structure of aceanthrene green, a pigment prepared by potassium hydroxide fusion of 1,9-anthracenedicarboxylic imide, was found to be incorrect. The structure of the pigment is reassigned to 7,8,15,16-dibenzo[a,j]perylenetetracarboxylic diimide on the basis of COSY, NOESY, and inversion–recovery 1H NMR experiments. N-Alkyl- or N-phenyl-1,9-anthracenedicarboxylic imides, aceanthryleno[1,2-b]quinoxaline, and a benzimidazole derivative of 1,9-anthracenedicarboxylic anhydride were found to give the same dibenzo[a,j]perylene structure when reacted in potassium hydroxide. The electronic spectra of these derivatives is reported and it is shown that, as predicted by Pariser–Parr–Pople calculations, they absorb in the near-infrared. Finally, a mechanistic outline for the fusion is proposed on the basis of AM1 and frontier molecular orbital calculations. Keywords: photoconductor, near-infrared, aceanthrene green, alkalifusion, polycyclic aromatic hydrocarbon.