Fluorescent compounds

A compound having a maximal fluorescence excitation wavelength, wherein the compound has a structure of Formula II:

• wherein:
• F is a moiety having the structure:
• Z− is a positive or negative counterion;
• Y is a bridge unit comprising a methine or polymethine unit that permits electron delocalization between F and Ψ;
• Ψ is a moiety having the structure:
• X1 and X4 are
• X2 and X3 are
• a and b are independently 0, 1, 2, or 3;
• R1, R2, R3, R4, R5, and R6 are each independently (R)p-(L)q-, wherein when at least two adjacent R1 and/or two adjacent R2 are present, the two adjacent R1 and/or the two adjacent R2 optionally form a fused 6-membered ring which is unsubstituted or substituted by one or more (R)p-(L)q-;
• R5 and R6 may optionally form a ring substituted with one or more (R)p-(L)q-, with the proviso that when the absorption maximum wavelength of the compound is less than 660 nm, then R5 and R6 do not form a substituted ring;
• each R of each (R)p-(L)q- of the compound is independently i) a reactive group capable of forming a covalent bond upon reacting with a reaction substrate, wherein said reaction substrate is a molecule having an amine, a thiol, a hydroxyl, an azide, an alkyne, an activated ester, or an aldehyde functional group, and wherein said reactive group is selected from the group consisting of an activated ester, a maleimide, an azide, an alkyne, a 1,3-diene, an aldehyde, an acyl azide, an acyl halide, an isothiocyanate, a halotriazine, a haloacetamide, an alkyl sulfonate, a methanethiosulfonate, a sulfonate ester, a phosphoramidite, an alkyl halide, a hydrazide, an acrylamide, and an epoxide;
• ii) a water soluble polymer which is a polyalkylene oxide;
• iii) an alkyl group, an aryl group, an alkylamino group, a dialkylamino group, an alkoxy group, a trifluoroalkyl group, a halogen group, a sulfonyl group, a sulfonate group, a phosphonate group or a sulfonamido group;
• or iv) —H;
• each L of each (R)p-(L)q- of the compound is independently a linking moiety formed of one or more chemical bonds and containing about 1-100 atoms;
• each p of each (R)p-(L)q- is independently an integer of about 1 to about 20;
• each q of each (R)p-(L)q- of R1 or R2 is independently an integer of 0 to about 20;
• each q of each (R)p-(L)q- of R3, R4, R5, R6, or R7 is independently an integer of 1 to about 20;
• c is 0 or 1;
• d is 0 or 1;
• at least one R of the (R)p-(L)q- of the compound is a reactive group capable of forming a covalent bond upon reacting with a reaction substrate;
• and
• at least one R of the (R)p-(L)q- of the compound is a water-soluble polymer which is a polyalkylene oxide radical.