A compound of Formula I: or Formula II: wherein R 1, R 2, R 3, R 4, R 5, and R 6 are each independently H, F, or sulfo; or two adjacent groups of R 1, R 2, R 3, R 4, R 5, or R 6 taken together with the atoms to which they are attached form a fused benzo ring that is optionally substituted with 1, 2, 3, or 4 alkyl, cycloalkyl, aryl, (aryl)alkyl, heteroaryl, amino, hydroxy, halo, sulfo, or -L-R x groups; each W 1 and W 2 taken together with the atoms to which it is attached is independently a 6-membered heterocyclic ring, wherein the ring optionally includes a second heteroatom selected from O, S, or N, wherein the N, if present, is substituted by H, alkyl, (aryl)alkyl, or -L-R x, and wherein at least one carbon atom of W 1 or W 2 is optionally substituted by R 7; each Y is independently CR 7 R 7, S, O, CF 2, or NR 7; each R 7 is independently H, (C 1 -C 8)alkyl, aryl, (aryl)alkyl, oxo, or -L-R x; each L is independently a direct bond or a linker, wherein the linker is a divalent radical of the formula -A-B-Z- wherein A is a direct bond or a (C 1 -C 12)alkyl chain optionally comprising one or more unsaturations, optionally substituted by one or more oxo (=O) groups, and optionally interrupted by one or more O atoms; B is a direct bond or a -NHC(=O)-, -C(=O)NH-, -OC(=O)-, -C(=O)O-, -O-, or -N(R 8)- group; and Z is a direct bond or a (C 1 -C 20)alkyl chain optionally comprising one or more unsaturations, optionally substituted by one or more oxo (=O) groups, and optionally interrupted by one or more O atoms; each R 8 is independently H, (C 1 -C 6)alkyl, or a nitrogen protecting group; R 9 is OPh-CO 2 H; -OPh-NH-(C 1 -C 12)alkyl-R x, or -OPh-C(=O)NH-(CH 2 CH 2 O) n (CH 2) m -R x, wherein n of R 9 is 1-6,and m of R 9 is 1-8; each R x is independently an activated ester of a carboxylic acid that includes a - C(=O)O- group covalently bonded to a succinimidyl, a sulfosuccinimidyl, a maleimide, or a 1-oxybenzotriazolyl group; -NH 2; -OH; -SO 2 Cl; -SO 2 Br; -SH; -B 2; -B 2 wherein R is alkyl or aryl; -O-P(N(alkyl) 2)(O-alkylene-CN); -N=C=O; -C(=O)-Cl; -C(=O)-Br; - C(=O)-I; -C(=O)H; -N 3; -C(=O)CN; a maleimide group; a diazirinyl group; an azidoaryl group; a psoralen derivative; a benzophenone; a 6'-O-linked-4-cyanobenzothiazole; a (C 1 -C 7)alkyl-methylene chloride; a (C 1 -C 7)alkyl-methylene bromide; a (C 1 -C 7)alkyl-methylene iodide; -CO 2 H; or -SO 3 H; provided that at least one -L-R x group is present and provided that at least one R x is not a sulfo group; wherein any alkyl, cycloalkyl, aryl, (aryl)alkyl, or heteroaryl is optionally substituted with one, two, or three halo, hydroxy, or sulfo groups; m is 0 or 1; n is 0,1, or 2; an organic or inorganic anion, present when the compound of Formula I or II is cationic; and each halo is selected from F, Cl, Br and I. R 1, R 2, R 3, R 4, R 5, and R 6 are each independently H, F, or sulfo; or two adjacent groups of R 1, R 2, R 3, R 4, R 5, or R 6 taken together with the atoms to which they are attached form a fused benzo ring that is optionally substituted with 1, 2, 3, or 4 alkyl, cycloalkyl, aryl, (aryl)alkyl, heteroaryl, amino, hydroxy, halo, sulfo, or -L-R x groups; each W 1 and W 2 taken together with the atoms to which it is attached is independently a 6-membered heterocyclic ring, wherein the ring optionally includes a second heteroatom selected from O, S, or N, wherein the N, if present, is substituted by H, alkyl, (aryl)alkyl, or -L-R x, and wherein at least one carbon atom of W 1 or W 2 is optionally substituted by R 7; each Y is independently CR 7 R 7, S, O, CF 2, or NR 7; each R 7 is independently H, (C 1 -C 8)alkyl, aryl, (aryl)alkyl, oxo, or -L-R x; each L is independently a direct bond or a linker, wherein the linker is a divalent radical of the formula -A-B-Z- wherein A is a direct bond or a (C 1 -C 12)alkyl chain optionally comprising one or more unsaturations, optionally substituted by one or more oxo (=O) groups, and optionally interrupted by one or more O atoms; B is a direct bond or a -NHC(=O)-, -C(=O)NH-, -OC(=O)-, -C(=O)O-, -O-, or -N(R 8)- group; and Z is a direct bond or a (C 1 -C 20)alkyl chain optionally comprising one or more unsaturations, optionally substituted by one or more oxo (=O) groups, and optionally interrupted by one or more O atoms; each R 8 is independently H, (C 1 -C 6)alkyl, or a nitrogen protecting group; R 9 is OPh-CO 2 H; -OPh-NH-(C 1 -C 12)alkyl-R x, or -OPh-C(=O)NH-(CH 2 CH 2 O) n (CH 2) m -R x, wherein n of R 9 is 1-6,and m of R 9 is 1-8; each R x is independently an activated ester of a carboxylic acid that includes a - C(=O)O- group covalently bonded to a succinimidyl, a sulfosuccinimidyl, a maleimide, or a 1-oxybenzotriazolyl group; -NH 2; -OH; -SO 2 Cl; -SO 2 Br; -SH; -B 2; -B 2 wherein R is alkyl or aryl; -O-P(N(alkyl) 2)(O-alkylene-CN); -N=C=O; -C(=O)-Cl; -C(=O)-Br; - C(=O)-I; -C(=O)H; -N 3; -C(=O)CN; a maleimide group; a diazirinyl group; an azidoaryl group; a psoralen derivative; a benzophenone; a 6'-O-linked-4-cyanobenzothiazole; a (C 1 -C 7)alkyl-methylene chloride; a (C 1 -C 7)alkyl-methylene bromide; a (C 1 -C 7)alkyl-methylene iodide; -CO 2 H; or -SO 3 H; provided that at least one -L-R x group is present and provided that at least one R x is not a sulfo group; wherein any alkyl, cycloalkyl, aryl, (aryl)alkyl, or heteroaryl is optionally substituted with one, two, or three halo, hydroxy, or sulfo groups; m is 0 or 1; n is 0,1, or 2; an organic or inorganic anion, present when the compound of Formula I or II is cationic; and each halo is selected from F, Cl, Br and I.