Water soluble porphyrin-Schiff base ligands and their metal complexes: Synthesis, photophysical, electrochemical, and chemosensor properties

In this work, 5-(4-aminophenyl)-10,15,20-tris(4-sulfonatophenyl)porphyrin trisodium salt was reacted with 4-R-2,6-diformyl phenol (R: -Me, -Et or -(t)butyl) to obtain dimeric porphyrin-Schiff base ligands as their sodium salts [Na-6(H5L1)-Na-6(H5L3). The Mn3+, Cu2+, and Zn2+ complexes of the water-soluble porphyrin-Schiff base ligands were also prepared, and their structures were characterized by the spectroscopic and analytical methods. The ligands exhibited H or J-aggregates with the change in pH. The water-soluble ligands showed reversible diffusion-controlled redox processes involving the pi-ring system of the porphyrin. The chemosensor properties of the ligands Na-6(H5L1)-Na-6(H5L3) towards cations or anions were studied by colorimetric and spectrophotometric methods. Na-6(H5L1) showed selective sensing abilities towards SO42- and Cu2+, while Na-6(H5L3) has selectivity for I-, Ag+, and Co2+ ions. The ligands were also tested as a fluorimetric probes for the detection of nitro-aromatic compounds [nitrobenzene (NB), 2,4-dinitrophenol (DNP) and 2,4,6-trinitrophenol (TNP)]. Na-6(H5L2) exhibits selective and sensitive sensing abilities for nitrobenzene with high quenching constants (K-sv = 3.80 x 10(6) M-1) and low detection limit (LOD = 0.0091 mu M).