Nicotinic acid and picolinic acid derived near-infrared fluorophores

A method of in vivo optical imaging, the method comprising:

• (a) administering to a subject a biocompatible fluorescent molecule comprising one or more biomolecules covalently linked to a fluorescent compound represented by formula (2):
• or a salt thereof, wherein:
• X is independently selected from the group consisting of C(CH2Y1)(CH2Y2), O, S, and Se;
• Y1 and Y2 are independently selected from the group consisting of H, C1-C20 aliphatic group and a C1-C20 aliphatic group wherein one or more methylene groups are replaced by O, S, or NH;
• W represents a benzo-condensed ring or a naphtho-condensed ring;
• R1 is selected from the group consisting of H, (CH2)xCH3, (CH2)nSO3− and (CH2)nSO3H, wherein x is an integer selected from 0 to 6 and n is an integer selected from 2 to 6;
• R4 is selected from the group consisting of H, (CH2)xCH3, (CH2)nSO3− and (CH2)nSO3H, wherein x is an integer selected from 0 to 6 and n is an integer selected from 2 to 6;
• R2 and R3 are independently selected from the group consisting of H, carboxylate, carboxylic acid, carboxylic ester, amine, amide, sulfonamide, hydroxyl, alkoxyl, a sulphonic acid moiety and a sulphonate moiety;
• Q is a heteroaryl ring substituted with —CO2H, —C(O)-halide, —C(O)O-benzotriazolyl, —C(O)O—N-succinimidyl, —C(O)O-tetrafluorophenyl, —C(O)O-pentafluorophenyl, —C(O)O-imidazolyl, or —C(O)O-p-nitrophenyl;
• or
• Q is selected from the group consisting of
• Q is a 6-membered heteroaryl ring substituted with —C(═O)R**, wherein R** is a saturated straight-chain hydrocarbon, a branched hydrocarbon, or a cyclic hydrocarbon;
• or
• Q is a carboxyl or carbonyl substituted 6-membered heteroaryl ring selected from the group consisting of pyridine, pyrimidone, pyrazine and pyridazine;
• and
• wherein the biomolecule is chemically linked to the fluorescent compound via reaction with Q thereby producing the biocompatible fluorescent molecule;
• (b) allowing time for the biocompatible fluorescent molecule to distribute within the subject or to contact or interact with a biological target within the subject;
• (c) illuminating the subject with light of a wavelength absorbable by the biocompatible fluorescent molecule;
• and
• (d) detecting the optical signal emitted by the biocompatible fluorescent molecule.