Functionalized Porphyrins as Red Fluorescent Probes for Metal Cations: Spectroscopic, MALDI-TOF Spectrometry, and Doped-Polymer Studies

The sensing ability of benzoporphyrins 1-5 and porphyrin-2-ylpyridines 6-10 towards different metal ions Na+, K+, Ca2+, Mg2+, Pb2+, Cu2+, Ni2+, Zn2+, Cd2+, Hg2+, and Cr3+ was explored in solution by absorption and fluorescence spectroscopy. Strong changes in the ground and excited state were detected only in the case of the soft metal ions Zn2+, Cd2+, Hg2+, and Cu2+. A one metal per ligand molar ratio was obtained in all cases for compounds1-5. In addition, a remarkable increase of the emission intensity for 1-5 was observed in the presence of Hg2+. In this series the highest association constant was obtained for compound1 (logK(ass)=(8.71 +/- 4.81)x10(-3)), which was able to quantify 32ppb of Hg2+. For compounds6-10 containing an additional pyridine unit, a metal-to-ligand stoichiometry of 1:2 was determined. The gas-phase detection abilities of compounds1-10 using MALDI-TOF-MS spectrometry confirmed that their sensorial ability and theoretical calculations are in accordance with the stoichiometry observed. Our preliminary studies show that some of the compounds supported in polymethylmethacrylate (PMMA) films can be used as promising metal-ion solid chemosensors; it was found that compound 1 in PMMA is able to distinguish between Zn2+ and Hg2+ in the solid phase.