Optical brightening agents and photographic materials which contain these brightening agents

摘要

New optical brightening agents and photographic materials which contain in at least one layer these brightening agents are provided. The compounds have the general formula wherein R1 and R3 are hydrogen or methyl, R2 and R4 are alkyl R5 is hydrogen, alkyl, aryl, aralkyl, X is -NH-, -O- or -S-, L1 and L2 are alkylene oxide chains and M(+) is a hydrogen or an alkali metal cation. These brightening agents enhance the brightness in the white areas of photographic print materials.