ABSORPTION-SPECTRUM SHIFT IN THE SOLID-STATE - A MO STUDY OF PYRROLOPYRROLE PIGMENT

The bathochromic shift in the spectrum of 1,4-dioxo-3,6-diphenylpyrrolo [3,4-c] pyrrole in the solid state relative to the spectra in solution was investigated by the semiempirical MO INDO/S method. On the basis of crystalline structure, the spectra for the monomer, dimers, and trimers invarious geometrically different conformations were calculated. The calculated spectral changes indicate that the intermolecular hydrogen bond plays an important role in the bathochromic shift. A detailed analysis of the components of notable transitions in aggregated systems is presented. The stabilities of the aggregated structures were estimated by the ab initio calculation. The intermolecular hydrogen bond was also found to be important for the formation of planar, crystalline structure. The sum of interactions in various dimer configurations provided an understanding of spectral properties and energetics on a molecular level in the solid state.