ELECTRONIC-SPECTRA OF 1,4-DIKETO-3,6-DIPHENYL-PYRROLO-[3,4-C]-PYRROLE IN THE SOLID-STATE

The title compound (DPP) is a new red pigment based on the diketopyrrolopyrrole chromophore. The evaporated film of DPP has a vivid red whose absorption spectrum is very similar to the molecular spectrum in solution. When exposed to acetone vapor, the film turns orange, and changes in photoelectrical properties take place. Electronic spectra of DPP have therefore been investigated mainly in evaporated films from the standpoint of pi-pi interactions along the stacking axis. Special attention has been paid to the temperature dependence of the absorption spectra in connection with lattice contractions. The effective overlap of pi-electrons between molecular planes strongly influences the electronic system and perturbs the molecular-like spectrum in the solid state. Several solid state spectra can arise from DPP, depending on the extent of the pi-pi interactions.