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

Abstract

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 ‐tbutyl) to obtain dimeric porphyrin‐Schiff base ligands as their sodium salts [Na6(H5L1)‐Na6(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 π‐ring system of the porphyrin. The chemosensor properties of the ligands Na6(H5L1)‐Na6(H5L3) towards cations or anions were studied by colorimetric and spectrophotometric methods. Na6(H5L1) showed selective sensing abilities towards SO42− and Cu2+, while Na6(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)]. Na6(H5L2) exhibits selective and sensitive sensing abilities for nitrobenzene with high quenching constants (Ksv = 3.80 × 106 M−1) and low detection limit (LOD = 0.0091 μM).