Study of Multiporphyrin Compounds as Colorimetric Sitting-Atop Metal Complexes: Synthesis and Photophysical Studies.

Mono-, di-, tri-, and hexaporphyrin derivatives were synthesized and their sensorial ability toward Na+ , Li+ , Ca2+ , Cu2+ , Ni2+ , Co2+ , Fe3+ , Zn2+ , Cd2+ , Hg2+ , Ag+ , Cr3+ , Pb2+ , and Al3+ was explored by absorption and emission spectroscopy and 1 H NMR spectroscopy. For all of the studied porphyrin derivatives the most significant spectral changes were observed upon addition of Zn2+ , Cd2+ , Cu2+ , Co2+ , Pb2+ , Hg2+ , and Fe3+ , which resulted in a color change from red to green. When the remaining metal ions were tested, no significant changes were observed. The results reveal, as expected, the formation of mononuclear complexes for porphyrin 4, dinuclear complexes for diporphyrin 7, and trinuclear complexes for triporphyrins 9 and 10. In addition, complexes of type M6 L were determined for hexaporphyrin 8. The NMR spectroscopy studies suggest that the interaction with the metals occurs with the formation of sitting-atop complexes. This study also shows that the sensitivity increases with increasing number of coordination sites, with the most pronounced case observed for Hg2+ . The lowest value of detectable concentration of 0.05 μm for Hg2+ was achieved for hexaporphyrin 8.