Patent ID: 7799122

Claim:
A compound of Formula (1) or a salt thereof: wherein: A 1 is optionally substituted phenyl; A 2 is optionally substituted aryl; Q 1 and Q 2 are each independently an optionally substituted phenylene ring which is para connected to the —N═N— and the —NR— groups shown in Formula (1); when present the substituents on Q 1 and Q 2 are selected from the group consisting of C 1-4 -alkoxy, C 1-4 -alkyl, —NHCONH 2 , —NHSO 2 —C 1-4 -alkyl, —SO 3 H and —PO 3 H 2 ; and each R independently is H or a substituent; with the provisos that: (i) the compound of Formula (1) has at least one group selected from the group consisting of —SO 3 H and —PO 3 H 2 groups; (ii) the compound of Formula (1) has more groups selected from the group consisting of —SO 3 H and —PO 3 H 2 groups than the total number of —CO 2 H and —COSH groups; and (iii) the compound of Formula (1) has only two azo groups.