Abstract: The present invention relates to a solid solution comprising (a) at least one compound according to formula (I), and (b) at least one compound according to formula (II), or at least one compound according to formula (III), or a mixture of at least one compound according to formula (II) and at least one compound according to formula (III), wherein R1 and R2 may, independently of one another, stand for —(CH2)n—X, wherein X stands for hydrogen, methyl, a C1-C5 alkoxyl, hydroxy, phenyl, C1-C5 alkylphenyl, C1-C5 alkoxyphenyl, hydroxyphenyl, halogenated phenyl, pyridyl, C1-C5 alkylpyridyl, C1-C5 alkoxypyridyl, halogenated pyridyl, pyridylvinyl or naphthyl; wherein n stands for 0, 1, 2, 3, 4 or 5; R3 and R4 may, independently of one another, stand for phenylene, C1-C5 alkylphenylene, C1-C5 alkoxyphenylene, hydroxyphenylene, halogenated phenylene, pyridinediyl, C1-C5 alkylpyridinediyl, C1-C5 alkoxy-pyridinediyl, halogenated pyridinediyl, anthraquinonediyl or naphthalenediyl, wherein the 2 nitrogen atoms bound to R3 a

Abstract: The present invention relates to a solid solution comprising (a) at least one compound according to formula (I) and (b) at least one compound according to formula (II), or at least one compound according to formula (III), or a mixture of at least one compound according to formula (II) and at least one compound according to formula (III) wherein R1 and R2 may, independently of one another, stand for —(CH2)n—X, wherein X stands for hydrogen, methyl, a C1-C5 alkoxyl, hydroxy, phenyl, C1-C5 alkylphenyl, C1-C5 alkoxyphenyl, hydroxyphenyl, halogenated phenyl, pyridyl, C1-C5 alkylpyridyl, C1-C5 alkoxypyridyl, halogenated pyridyl, pyridylvinyl or naphthyl; wherein n stands for 0, 1, 2, 3, 4 or 5; R3 and R4 may, independently of one another, stand for phenylene, C1-C5 alkylphenylene, C1-C5 alkoxyphenylene, hydroxyphenylene, halogenated phenylene, pyridinediyl, C1-C5 alkylpyridinediyl, C1-C5 alkoxy-pyridinediyl, halogenated pyridinediyl, anthraquinonediyl or naphthalenediyl, wherein the 2 nitrogen atoms bound to R4 acc