Diketopyrrolopyrroles of the formula (I):
##STR1##
wherein
R1, R2, R3 and R4 independently
of one another are a C1-C4 alkyl radical or a substituted
or unsubstituted phenyl radical, wherein the phenyl radical can be substituted
by 1, 2, 3 or 4 substituents from the group C1-C4 alkyl,
C1-C4 alkoxy, CN, F, Cl, Br, NO2, CF3,
S—C1-C4 alkyl, phenyl or (C1-C2)alkylenephenyl,
with the proviso that at least one of the radicals, R1, R2,
R3, or R4, is one of the stated substituted or unsubstituted
phenyl radicals.
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