“Synthesis and photophysical properties of water-soluble sulfonato-Salen-type Schiff bases and their applications of fluorescence sensors for Cu²⁺ in water and living cells”, Anal. Chim. Acta, 2012, 735, 96 - 106.

L. Zhou, P. Y. Cai, Y. Feng, J. H. Cheng, H. F. Xiang,* J. Liu,* D. Wu,* X. G. Zhou

► Sulfonate groups ensure good stability and solubility in water. ► Sulfonate groups have little effect on the photophysical properties. ► This is confirmed by the TD-DFT calculations and experimental results. ► The strong blue, green, or orange fluorescence is selectively quenched by Cu²⁺. ► The ligands are sensitive fluorescence sensors for Cu²⁺ in water and living cells.

A series of water-soluble sulfonato-Salen-type ligands derived from different diamines including 1,2-ethylenediamine (Et-1-Et-4), 1,2-cyclohexanediamine (Cy-1 and Cy-2), 1,2-phenylenediamine (Ph-1-Ph-3 and PhMe-1-PhMe-4), and dicyano-1,2-ethenediamine (CN-1) has been designed and prepared. Sulfonate groups of ligands ensure good stability and solubility in water without affecting their excited state properties. These ligands exhibit strong UV/Vis-absorption and blue, green, or orange fluorescence. Time-dependent-density functional theory calculations have been undertaken to reveal the influence of ligand nature, especially sulfonate groups, on the frontier molecular orbitals. Since their fluorescence is selectively quenched by Cu²⁺, the sulfonato-Salen-type ligands can be used as highly selective and sensitive turn-off fluorescence sensors for the detection of Cu²⁺ in water and fluorescence imaging in living cells.