Abstract: Quaterrylenetetracarboxylic diimides I whereR is hydrogen;C.sub.1 -C.sub.30 -alkyl whose carbon chain may be interrupted by one or more of --O--, --S--, --NR.sup.1 --, --CO-- and/or --SO.sub.2 -- and which may be monosubstituted or polysubstituted by cyano, C.sub.1 -C.sub.6 -alkoxy or a 5-, 6- or 7-membered heterocyclic radical which is attached via a nitrogen atom and which may contain further heteroatoms and may be aromatic, whereR.sup.1 is hydrogen or C.sub.1 -C.sub.6 -alkyl;C.sub.5 -C.sub.8 -cycloalkyl whose carbon skeleton may be interrupted by one or more of --O--, --S-- and/or --NR.sup.1 --;aryl or hetaryl, which may each be monosubstituted or poly-substituted by C.sub.1 -C.sub.18 -alkyl, C.sub.1 -C.sub.6 -alkoxy, cyano, --CONHR.sup.2, --NHCOR.sup.2 and/or aryl- or hetaryl-azo, which may each be substituted by C.sub.1 -C.sub.10 -alkyl, C.sub.1 -C.sub.6 -alkoxy or cyano, whereR.sup.2 is hydrogen; C.sub.1 -C.sub.18 -alkyl; aryl or hetaryl, which may each be substituted by C.sub.1 -C.sub.6 -alkyl, C.sub.