TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (Claimed): Compound (I) is prepared by saponifying Rx residue of rylene diimide compound of formula (IV) under basic conditions and removing imide group of Rx to obtain perylene monoimide monoanhydride compound of formula (V); removing monoanhydride group of compound (V) by imidization with 1,2-alkyl diamine or 3-aminoalkanoic acid to obtain monofunctionalized perylene of formula (VI); and sulfonating compound (VI) under acidic conditions to obtain intermediate product, and reacting the intermediate product with a compound providing a coupling group. Water-soluble nitrilotriacetic acid-functionalized rylene dye may be prepared by reacting a compound having activated ester coupling group in solution with a compound providing protected nitrilotriacetic acid group, and subsequently removing the protective groups to obtain compound (I) in which the coupling group is nitrilotriacetic acid; or coupling carboxy-functionalized rylene derivative with nitrilotriacetic acid moiety by amide bond formation in solid phase.R1, Rx=organic residue which is attached to N atom via C atom;R4-R7=H or organic residue;R2=-(CH2)qCOOH or -(CH2)qNHR8;q=1-20; andR8=H or 1-10C alkyl.Preferred Components: The linking group A is of formula -C(O)-O-, -C(O)-N(R3)-, or -N(R3)-C(O)-.R3=H or 1-10C alkyl. Preferred Definitions:    n=2-4;    E=N-hydroxysuccinimide ester, maleimide, nitrilotriacetic acid, or thioester or thiol;    R1=phenyl, pyridyl, or naphthyl residue which optionally contains substituent(s); and    at least two of R4-R7=phenyl residues.    EXAMPLE - Potassium hydroxide (148 g) in water (130 ml) was added to a solution of N,N'-bis(2,6-diisopropylphenyl)-1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarboxydiimide (7.56 g) in 2-propanol (1 L). The mixture was refluxed under argon at 110 degrees C for 12 hours. After cooling to room temperature, the solution was poured into hydrochloric acid/water (60 ml/3.5 L). The precipitate was filtered and dried under vacuum at 60 degrees C. The solid was dissolved in acetic acid (100 ml) and refluxed at 80 degrees C for 30 minutes. Water (150 ml) was added. The precipitate was filtered and purified to obtain N-(2,6-diisopropylphenyl)-1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarboxy-9,10-monoanhydride-3,4-monoimide (1a) as red solid. Compound (1a) (200 mg) and 1,2-ethylenediamine (130 mg) were added to toluene (20 ml). The mixture was stirred under argon at 60 degrees C for 3 hours. Following reduction of solvent, the material was purified to obtain N-(2,6-diisopropylphenyl)-N'-(4-aminoethyl)-1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarboxydiimide (1b) as red solid. Compound (1b) (100 mg) was added to concentrated sulfuric acid (3 ml), and the mixture was stirred at room temperature for 16 hours. Water was slowly added, and the resulting solution was dialyzed in water and freeze dried to obtain N-(2,6-diisopropylphenyl)-N'-(4-aminoethyl)-1,6,7,12-tetra (4-sulfophenoxy)-perylene-3,4:9,10-tetracarboxydiimide as red solid (yield: 97%).