Investigation of the spectral properties of a squarylium near-infrared dye and its complexation with Fe(III) and Co(II) ions

The spectral features of the squarylium near-infrared (NIR) dye NN525 in different solutions and its complexation with several metal ions were investigated. The absorbance maximum of the dye is lambda = 663 nm in methanol. This value matches the output of a commercially available laser diode (650 nm), thus making use of such a source practical for excitation. The emission wavelength of the dye in methanol is lambda(em) = 670 nm. The addition of either Fe(III) ion or Co(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 = 2.70 x 10(7) M-1 for Co(II) ion. The K-SV value for Fe(III) ion could not be established due to the non-linearity of the Stern-Volmer plot and the modified Stern-Volmer plot for this ion. The detection limit is 6.24 x 10(-8) M for Fe(III) ion and 1.55 x 10(-5) M for Co(III) 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 3.14 x 10(6) M-1 for the Fe-dye complex and 2.64 x 10(5) M-1 for the Co-dye complex. (C) 2000 Elsevier Science B.V. All rights reserved.