Spectral characterization of a novel near-infrared cyanine dye: a study of its complexation with metal ions

The spectral features of the near-infrared (NIR) dye TG-170 in different solutions and its complexation with several metal ions were investigated. The absorbance maxima of the dye are at λ=819, 805, and 791 nm in dimethyl sulfoxide (DMSO), methanol, and a buffer of pH 5.9, respectively. These values match the output of a commercially available laser diode (780 nm), thus making use of such a source practical for excitation. The emission wavelengths of the dye are at λ_em =822, 812, and 803 nm in DMSO, methanol, and the buffer, respectively. The molar absorptivity and fluorescence quantum yield increase accordingly. The addition of either an Al(III) ion or Be(II) ion resulted in fluorescence quenching of the dye. The Stern–Volmer quenching constant, K_SV, was calculated from the Stern–Volmer plot to be K_SV=3.11×10⁵ M⁻¹ for the Al(III) ion and K_SV=1.17×10⁶ M⁻¹ for the Be(II) ion. The molar ratio of the metal to the dye was established to be 1:1 for both metal ions. The stability constant, K_S, of the metal–dye complex was calculated to be 4.37×10⁴ M⁻¹ for the Al–dye complex and 1.94×10⁶ M⁻¹ for the Be–dye complex.