A compound of the formula (I) wherein Z is O, S, or NR.sub.35 wherein R.sub.35 is H or alkyl; R.sub.1-R.sub.5 are each independently H, alkyl, halo, carboxyl, amino, or SO.sub.3.sup.-Cat.sup.+, wherein Cat.sup.+ is a cation and at least one of R.sub.1-R.sub.5 is SO.sub.3.sup.-Cat.sup.+; R.sub.6 and R.sub.7 are each H, alkyl, or optionally, together with the (a) group to which they are bonded, form a ring; m and n are each independently integers from 0 to 5; X and Y are each independently O, S, Se or CR.sub.19R.sub.20, wherein R.sub.19 and R.sub.20 are each independently alkyl, or optionally form a ring together with the carbon atom to which they are bonded; R.sub.8 and R.sub.13 are each independently alkyl, (CH.sub.2).sub.rR.sub.25 or (CH.sub.2).sub.rR.sub.18; wherein at least one of R.sub.8 and R.sub.13 (CH.sub.2).sub.rR.sub.18 and wherein r is an integer from 1 to 50, and R.sub.25 is a functional group that does not directly react with a carboxyl, hydroxyl, amino, or a thiol group, and R.sub.18 is a functional group that can react with a carboxyl, hydroxyl, amino, or thiol group; and R.sub.9-R.sub.12 and R.sub.14-R.sub.17 are each independently H, alkyl, halo, amino, sulfonato, R.sub.21 COOH, R.sub.21OR.sub.22, R.sub.21SR.sub.22, or R.sub.21COOR.sub.22 wherein R.sub.21 is a bond or alkylene and R.sub.22 is alkyl, or optionally R.sub.11 and R.sub.12 together with the atoms to which they are bonded form an aromatic ring, or optionally R.sub.16 and R.sub.17 together with the atoms to which they are bonded form an aromatic ring. Methods of dye-labeling biomolecules with the compound of formula (I) and dye-labeled biomolecules are also provided.