Characterization of a novel crown ether-bearing near-infrared heptamethine cyanine dye. A study of fluorescence quenching by lithium

The spectral characteristics of a crown ether-bearing heptamethine cyanine dye (JCM-15C5) and its quenching by lithium ion are reported. The absorbance maximum of the dye is at 776 nm in acetonitrile. This value matches the output of a commercially available laser diode (780 nm), thus making use of such a source practical for excitation. The emission wavelength of the dye in acetonitrile is at 799 nm. It was found that Li⁺ ion selectively quenches the fluorescence intensity of JCM-15C5 by the static quenching mechanism. The Stern-Volmer quenching constant (K_sv) was calculated from the Stern-Volmer plot and found to be 1.17×10⁷ M⁻¹ at room temperature. The detection limit for Li⁺ ion was found to be 7.43×10⁻² ppb. The stability constant (K_s) of the metal-dye complex was determined by fluorometric titration and found to be 5.40×10⁷ M⁻¹.