A pharmaceutical composition comprising: (i) a conjugate containing a phthalocyanine dye linked to a targeting molecule; and (ii) a pharmaceutically acceptable excipient; wherein the targeting molecule binds to a cell surface target molecule on a surface of a cell or pathogen, wherein the phthalocyanine dye comprises the formula: wherein: L is a linker; Q is a reactive group for attachment of the dye to the targeting molecule; R 2, R 3, R 7, and R 8 are each independently selected from among optionally substituted alkyl and optionally substituted aryl; R 4, R 5, R 6, R 9, R 10, and R 11 are each independently selected from among hydrogen, optionally substituted alkyl, optionally substituted alkanoyl, optionally substituted alkoxycarbonyl, optionally substituted alkylcarbamoyl, and a chelating ligand, wherein at least one of R 4, R 5, R 6, R 9, R 10, and R 11 comprises a water soluble group; R 12, R 13, R 14, R 15, R 16, R 17, R 18, R 19, R 20, R 21, R 22 and R 23 are each independently selected from among hydrogen, halogen, optionally substituted alkylthio, optionally substituted alkylamino and optionally substituted alkoxy; and X 2 and X 3 are each independently C 1 -C 10 alkylene, optionally interrupted by a heteroatom; and wherein greater than 90% or greater than 95% of the conjugate is present as a main monomer component. (i) a conjugate containing a phthalocyanine dye linked to a targeting molecule; and (ii) a pharmaceutically acceptable excipient; wherein the targeting molecule binds to a cell surface target molecule on a surface of a cell or pathogen, wherein the phthalocyanine dye comprises the formula: wherein: L is a linker; Q is a reactive group for attachment of the dye to the targeting molecule; R 2, R 3, R 7, and R 8 are each independently selected from among optionally substituted alkyl and optionally substituted aryl; R 4, R 5, R 6, R 9, R 10, and R 11 are each independently selected from among hydrogen, optionally substituted alkyl, optionally substituted alkanoyl, optionally substituted alkoxycarbonyl, optionally substituted alkylcarbamoyl, and a chelating ligand, wherein at least one of R 4, R 5, R 6, R 9, R 10, and R 11 comprises a water soluble group; R 12, R 13, R 14, R 15, R 16, R 17, R 18, R 19, R 20, R 21, R 22 and R 23 are each independently selected from among hydrogen, halogen, optionally substituted alkylthio, optionally substituted alkylamino and optionally substituted alkoxy; and X 2 and X 3 are each independently C 1 -C 10 alkylene, optionally interrupted by a heteroatom; and wherein greater than 90% or greater than 95% of the conjugate is present as a main monomer component. L is a linker; Q is a reactive group for attachment of the dye to the targeting molecule; R 2, R 3, R 7, and R 8 are each independently selected from among optionally substituted alkyl and optionally substituted aryl; R 4, R 5, R 6, R 9, R 10, and R 11 are each independently selected from among hydrogen, optionally substituted alkyl, optionally substituted alkanoyl, optionally substituted alkoxycarbonyl, optionally substituted alkylcarbamoyl, and a chelating ligand, wherein at least one of R 4, R 5, R 6, R 9, R 10, and R 11 comprises a water soluble group; R 12, R 13, R 14, R 15, R 16, R 17, R 18, R 19, R 20, R 21, R 22 and R 23 are each independently selected from among hydrogen, halogen, optionally substituted alkylthio, optionally substituted alkylamino and optionally substituted alkoxy; and X 2 and X 3 are each independently C 1 -C 10 alkylene, optionally interrupted by a heteroatom; and wherein greater than 90% or greater than 95% of the conjugate is present as a main monomer component.