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 , Ca , Mg , Pb , Cu , Ni , Zn , Cd , Hg , and Cr 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 Zn , Cd , Hg , and Cu . A one metal per ligand molar ratio was obtained in all cases for compounds 1-5. In addition, a remarkable increase of the emission intensity for 1-5 was observed in the presence of Hg . In this series the highest association constant was obtained for compound 1 (log K =(8.71±4.81)×10 ), which was able to quantify 32 ppb of Hg . For compounds 6-10 containing an additional pyridine unit, a metal-to-ligand stoichiometry of 1:2 was determined. The gas-phase detection abilities of compounds 1-10 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 Zn and Hg in the solid phase.