Geometry and absorption of diketo-pyrrolo-pyrrole isomers and their π-isoelectronic furo-furanone analogues

The relation between geometry and absorption spectra of diketo-pyrrolo-pyrrole isomers and their π-isoelectronic furo-furanone analogues was studied both experimentally and theoretically. The DFT computed geometries reasonably agree with the published X-ray results. An efficient coupling of phenyl groups with diketo-pyrrolo-pyrrole and furo-furanone central unit was found for P.R. 255 and its O-analogue, while much weaker coupling occurs in pulvinic dilactone and its N-analogue. The ability of PCM TD DFT to predict the absorption maxima in DMSO is discussed with respect to underestimation of the charge-transfer character of the compounds and overestimation of conjugation effect.