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A process for converting perylene-3,4:9,10-tetracarboximides of the general formula I in which Rand Rare each unbranched, branched or cyclic C-C-alkyl to a form suitable for use as fluorescent dyes, which comprises

Conversion of perylene-3,4:9,10-tetracarboximides to a form suitable for use as fluorescent dyes

Novel crystalline forms of and a process for converting perylene-3,4:9,10-tetracarboximide of the general formula I to a form used as a fluorescent dye. The process including: a) dissolving or suspending the perylene-3,4:9,10-tetracarboximide in a solvent to obtain a solution or suspension; and b1) cooling the solution obtained in step a) to a temperature at or below the crystallization temperature of the perylene-3,4:9,10-tetracarboximide and, if the solvent is organic, removing excess solvent until the first crystals form, otherwise, adding water or dilute aqueous solutions of the solvent until the first crystals form, and maintaining the solution at that temperature for further crystallization; or b2) cooling the suspension obtained in step a) to or below the crystallization temperature when the temperature in step a) was above the crystallization temperature, and maintaining the suspension at the temperature for further crystallization to form one or more solvate crystals.

Method for converting perylen-3,4:9,10-tetracarboxylic acid diimides into a form suitable for use as a fluorescent dye

A 1,7-disubstituted perylene-3,4,9,10-tetracarboxylic diimide of the general formula VI:

1,7-Diaroxy- or 1,7-arylthio-substituted perylene-3,4,9,10-tetracarboxylic acids, their dianhydrides and diimides

A 1,7-disubstituted perylene-3,4,9,10-tetracarboxylic diimide of the general formula VI

1,7-disubstituted perylene-3,4,9,10-tetracarboxylic acids, their dianhydrides and diimides

1,7-diaroxy- or 1,7-arylthio-substituted

Process for producing perylene-3, 4-dicarboxylic acid imides

1,7-disubstituted perylene-3,4,9, 10-tetracarboxylic acids, their

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