Biocompatible alkyne arms containing Schiff base fluorescence indicator for dual detection of Cd and Pb at physiological pH and its application to live cell imaging

An alkyne arms containing salen-type Schiff base ligand, 6,6′-((1 E ,1′ E )-(1,2-phenylenebis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(3-(prop-2-yn-1-yloxy)phenol) ( H 2 L ), is reported here as a dual chemosensor for Cd II and Pb II ions. The ligand H 2 L was characterized by various spectral methods. The ligand H 2 L acts as a dual sensor for Cd II and Pb II in methanol/HEPES buffer (5 mM, pH 7.3; 1 : 9 v/v) at room temperature with well-separated excitation and emission wavelengths. The emission intensity at 553 nm of H 2 L is shifted and a new band appeared at 578 nm with the increase in the presence of Cd II when it is excited at 420 nm. With excitation at 410 nm, the emission intensity of H 2 L at 485 nm shifted and a new band appeared at 505 nm with the increase in the presence of Pb II . The quantum yield of H 2 L increases considerably in the presence of Cd II and Pb II . The compound H 2 L is non-fluorescent; however, in the presence of Cd II and Pb II , the compound H 2 L is highly fluorescent with well-separated excitation and emission wavelengths, indicating that the metal ion is coordinated through phenolic oxygen and imine nitrogen of the Schiff base blocking the PET (Photoinduced Electron Transfer) process and stimulating the CHEF (Chelation Enhanced Fluorescence) process, to increase the fluorescence intensity of H 2 L . The detection limit values of H 2 L are in a nano-molar range for both metal ions, confirming very high sensitivity of H 2 L . The L·M II binding mode and the recognition mechanism of the sensor were explored by Job's plot, 1 H NMR, FT-IR, pH and DFT calculations. Besides, H 2 L was successfully utilized in cell imaging studies for both metal ions in MCF 7 cells. An alkyne arms containing salen-type Schiff base ligand L acts as a dual sensor for Cd II and Pb II with well-separated excitation and emission wavelengths. The ligand L has been utilized in cell imaging studies for both metal ions.