Fluorescence properties of polyamines bearing two terminal quinoline fragments in water

Fluorescence properties of polyamines bearing two terminal quinoline fragments with different polyamine chain length, such as ethylenediamine (L0), diethylenetriamine (L1), and triethylenetetramine (L2), have been studied in water. These ligands show Zn2+-induced fluorescence enhancement, while showing almost no enhancement with other cations. However, stability constants for Zn2+ coordination and fluorescence response against Zn2+ depend strongly on the polyamine chain length. The chain length also affects the fluorescence wavelength. The Zn2+–L1 and Zn2+–L2 complexes show emission at 410 nm, while Zn2+–L0 complexes show a blue-shifted emission at 375 nm due to the partial charge transfer from the excited state quinoline to the Zn2+ center.