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 dye NN525 in different solutions and its complexation with several metal ions were investigated. The absorbance maximum of the dye is at 669 nm in tetrahydrofuran. 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 maximum of the dye in tetrahydrofuran is at 676 nm. The addition of either Fe(III) ion or Co(II) ion resulted in fluorescence quenching of the dye. The detection limit is 6.24×10 −8 M for Fe(III) ion and 1.55×10 −8 M for Co(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 3.14×10 6 M −1 for the Fe–dye complex and 2.64×10 5 M −1 for the Co–dye complex.