The present invention relates to fluorescent diketopyrrolopyrroles ("DPPs") of the formula ##STR00001## characterized in that that at least two adjacent substituents R.sup.5 to R.sup.11 form an aromatic or aliphatic fused ring system, or at least one substituent R.sup.5 to R.sup.11 is cycloalkyl, aralkyl, alkenyl, cycloalkenyl, alkynyl, a hydroxyl group, a mercapto group, alkylthio, an aryl thioether group, a heterocyclic group, halogen, haloalkyl, haloalkenyl, haloalkynyl, a cyano group, an aldehyde group, a carbonyl group, a carboxyl group, an ester group, a carbamoyl group, a nitro group, a silyl group, a siloxanyl group, a substituted or unsubstituted vinyl, arylamino or diarylamino group; a process for their preparation and their use for the preparation of inks, colorants, pigmented plastics for coatings, non-impact-printing material, color filters, cosmetics, or for the preparation of polymeric ink particles, toners, dye lasers and electroluminescent devices.The fluorescent diketopyrrolopyrroles ("DPPs") of the formula I exhibit a high lighffastness, a high heat stability, especially in plastics. A luminescent device comprising a DPP compound of formula I is high in the efficiency of electrical energy utilisation, high in luminance and high in colour purity.