A compound of formula I: wherein Z is H, F, Cl, Br, I, CN, amino, alkylamino, dialkylamino, alkyl ester, carboxy, carboxylic acid salt, alkyl amide, phosphate, alkyl phosphate, sulphate, alkyl sulfonate, nitro, or (C 1 -C 10)alkyl optionally unsaturated and optionally substituted with amino, hydroxy, oxo (=O), nitro, thiol, or halo; each R 1 is independently H, F, Cl, Br, I, CN, (C 1 -C 6)alkyl, (C 1 -C 6)alkoxy or (C 1 -C 6)alkylthio, wherein each alkyl, alkoxy, or alkylthio is optionally substituted with F, Cl, Br, I, amino, alkenyl, alkynyl, cycloalkyl, aryl, alkyl sulfonate, or CO 2 M wherein M is H, an organic cation, or an inorganic cation; n is 0, 1, or 2; Y is a linking group comprising (C 1 -C 16)alkyl optionally substituted with one or more halo, oxo (=O), (C 1 -C 6)alkyl, or (C 1 -C 6)alkoxy, and optionally interrupted with one or more N(R 1), O, S, or -N-C(=O)- groups; and X is biotin, a resin, a fluorophore, a chromophore, fluorescein, rhodamine, BODIPY, rhodamine green, infrared dyes, borapolyazaindacenes, coumarins, xanthenes, cyanines, iron-oxide particles, a sepharose or cellulose bead, a membrane, glass, cellulose, plastic or other synthetically prepared polymer, self assembled monolayers, a surface plasmon resonance chip, a chelating agent, 1-[2-amino-5-(2,7 -dichioro-6-hydroxy-3-oxy-9-xanthenyl)-phenoxy]-2-(2'-amino-5'-methylphenoxy)ethane-N,N,N',N'-tetraacetic acid (Fluo-3), 1,3-benzenedicarboxylic acid, 4,4'-[1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7, 16-diylbis(5-methoxy-6,2-benzofurandiyl)]bis (PBFI), 4-amino-5-methylamino-2',7'-difluorescein, R110, rhodols, CRG6, Texas Methyl Red (carboxytetramethylrhodamine), 5-carboxy-X-rhodamine, dansyl fluorophores, fluorescent acridinium moieties, benzopyrene based fluorophores, 7-nitrobenz-2-oxa-1,3-diazole, 3-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-2,3-diamino-propionic acid, ruthenium chelates dimethylaminoazosulfonic acid (DABSYL), dimethylaminoazo-carboxylic acid (DABCYL), or difluoroboradiazaindacenes. Z is H, F, Cl, Br, I, CN, amino, alkylamino, dialkylamino, alkyl ester, carboxy, carboxylic acid salt, alkyl amide, phosphate, alkyl phosphate, sulphate, alkyl sulfonate, nitro, or (C 1 -C 10)alkyl optionally unsaturated and optionally substituted with amino, hydroxy, oxo (=O), nitro, thiol, or halo; each R 1 is independently H, F, Cl, Br, I, CN, (C 1 -C 6)alkyl, (C 1 -C 6)alkoxy or (C 1 -C 6)alkylthio, wherein each alkyl, alkoxy, or alkylthio is optionally substituted with F, Cl, Br, I, amino, alkenyl, alkynyl, cycloalkyl, aryl, alkyl sulfonate, or CO 2 M wherein M is H, an organic cation, or an inorganic cation; n is 0, 1, or 2; Y is a linking group comprising (C 1 -C 16)alkyl optionally substituted with one or more halo, oxo (=O), (C 1 -C 6)alkyl, or (C 1 -C 6)alkoxy, and optionally interrupted with one or more N(R 1), O, S, or -N-C(=O)- groups; and X is biotin, a resin, a fluorophore, a chromophore, fluorescein, rhodamine, BODIPY, rhodamine green, infrared dyes, borapolyazaindacenes, coumarins, xanthenes, cyanines, iron-oxide particles, a sepharose or cellulose bead, a membrane, glass, cellulose, plastic or other synthetically prepared polymer, self assembled monolayers, a surface plasmon resonance chip, a chelating agent, 1-[2-amino-5-(2,7 -dichioro-6-hydroxy-3-oxy-9-xanthenyl)-phenoxy]-2-(2'-amino-5'-methylphenoxy)ethane-N,N,N',N'-tetraacetic acid (Fluo-3), 1,3-benzenedicarboxylic acid, 4,4'-[1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7, 16-diylbis(5-methoxy-6,2-benzofurandiyl)]bis (PBFI), 4-amino-5-methylamino-2',7'-difluorescein, R110, rhodols, CRG6, Texas Methyl Red (carboxytetramethylrhodamine), 5-carboxy-X-rhodamine, dansyl fluorophores, fluorescent acridinium moieties, benzopyrene based fluorophores, 7-nitrobenz-2-oxa-1,3-diazole, 3-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-2,3-diamino-propionic acid, ruthenium chelates dimethylaminoazosulfonic acid (DABSYL), dimethylaminoazo-carboxylic acid (DABCYL), or difluoroboradiazaindacenes.