Optical brightening agents

A compound in free acid or salt form of the formula I ##STR5## wherein R, R.sub.1 are moieties which are the same or different and have the formula --NR.sub.2 R.sub.3,

• wherein:
• (a) R.sub.2 is selected from
• (i) hydrogen;
• (ii) C.sub.1-6 alkyl, optionally substituted with at least one of mercapto, C.sub.1-6 alkylthio, OH and SO.sub.3 M;
• and
• (iii) --R.sub.4 (CO.sub.2 M).sub.x
• wherein R.sub.4 is an aliphatic moiety having from 1-6 carbon atoms, those valences not bonded with groups CO.sub.2 M being bonded with at least one of H, mercapto, C.sub.1-6 alkylthio, OH and
• SO.sub.3 M, x is an integer of from 1-4 and M is selected from hydrogen, or a colourless cation;
• with the provisos that, when R.sub.2 is selected only from (i) or (ii), any group
• (ii) is substituted with at least both of OH and SO.sub.3 M;
• (b) R.sub.3 is as defined in R.sub.2 with the proviso that R.sub.2 and R.sub.3 cannot both be hydrogen, and when one of R.sub.2, R.sub.3 is hydrogen, the other cannot be --(CH.sub.2 CO.sub.2 H);
• or R.sub.2 and R.sub.3 together with the nitrogen atom form a pyrrolidine ring, said ring is singly substituted with --COOM or --SO.sub.3 M;
• and R.sub.5 is selected from the group consisting of hydrogen, methyl, C.sub.1-6 alkoxy and halogen.