Correlation between crystal and electronic structures in dithioketopyrrolpyrrole pigment (DTPP) has been reviewed on the basis of the molecular exciton theory as well as on the polarized reflection measurements on single crystals. The mechanism of the near-IR absorption of DTPP has been clarified as arising from the molecular arrangement of “bricks in a brick wall” structure as characterized by J-aggregates in cyanine dyestuffs.
