Cpds. (I) of formulae (A-NR1-Z-NR2)n-X (IA), A-NR1-Z1-N=N-KK (IB) and A-NR1-Z2-NR2-A1 (IC); and cpds. of formula A-NR1-Z-NR2-H (II), all of which contain 4-(imidazolium-2-azo)-phenyl gp(s)., are claimed. In the formulae, A and A1 = are each a 4-(imidazolium-2-azo)-phenyl gp. of formula (III); Z is a radical of an aliphatic or aromatic diamine; Z1 is a radical of an aromatic diamine; Z2 is a radical of an aliphatic diamine; R1-R4 are each H or opt. substd. 1-4C alkyl; or NR1-Z-NR2 or NR1-Z2-NR2 form a 5-, 6- or 7-membered ring; R5 and R6 are each H or opt. substd. 1-4C alkyl or 1-4C alkoxy; KK is a radical of coupling component; X is a bridging gp.; n = 2, 3 or 4; and An is a colourless anion. Also claimed are (i) paper dyed with (I); (ii) solid and liq. formulations contg. dye(s) (I) for dyeing paper; and (iii) dye mixts. contg. (I) and cationic Cu phthalocyanine (CuPc) dye.