N-substituted 1,4-diketopyrrolo-[3,4-c]-pyrroles

A compound of the formula I

• in which R.sub.1 and R.sub.2 are phenyl or said phenyl substituted by one or two fluorine, chlorine or bromine atoms or mixtures thereof, by one, two or three methyl or methoxy groups or mixtures thereof with chlorine atoms, by cyano, by dimethylamino, by trifluoromethyl, by tert-butyl, by hydroxy, by alkoxycarbonyl of 2 to 3 carbon atoms, by benzoylamino or by acetyl;
• naphthyl or said naphthyl substituted by methoxy;
• anthryl or phenanthryl;
• and
• R.sub.3 and R.sub.4 are both other than hydrogen and are C.sub.1 -C.sub.12 -alkyl, C.sub.2 -C.sub.13 -alkoxycarbonyl, carboethoxymethyl, cyanomethyl, benzoyl, benzyl, allyl, phenyl or said phenyl substituted by chlorine or by bromine, or the group of the formula ##STR36## in which R.sub.1 and R.sub.2 are as defined above, R.sub.17 is hydrogen and R.sub.18 is a divalent radical derived from a C.sub.1 -C.sub.8 -dihaloalkane, C.sub.1 -.sub.10 -dicarboxylic acid halide, phenylene dihalide or xylylene dihalide.