| abstract |
Disclosed are compounds of formula I <IMAGE> I in which R1 and R4, independently, are hydrogen, a non-chromophoric second order substituent, or alkyl or alkenyl unsubstituted or substituted by a non-chromophoric group, R2 and R5, independently, are hydrogen or alkyl or alkenyl, unsubstituted or substituted by a non-chromophoric group, R3 and R6, independently, are hydrogen, alkyl, carboxyl or a non-chromophoric esterified carboxyl group, or R2, together with R3, and/or R5 together with R6, signify an alkylene bridge, R7 and R8, independently, signify hydrogen or a non-chromophoric substituent, or, when R7 is in the 3-position and/or R8 in the 3' position, R7 together with R2, and/or R8 together with R5 signify an alkylene bridge, with the proviso that no more than one of R1 and R2 and no more than one of R4 and R5 signify hydrogen, their production and use as optical brightening agents. |