New coumarin–corrole and –porphyrin conjugate multifunctional probes for anionic or cationic interactions: synthesis, spectroscopy, and solid supported studies

Corroles and porphyrins are very promising probes to be used as materials for anion and metal ion detection. Here, we present the synthesis and characterization of two new corrole–coumarin derivatives 7–8 and some porphyrin–coumarin analogs 3–6. The sensing ability of the metalloconjugates was studied in the presence of spherical (F−, Cl−), linear (CN−), and bulky anions (CH3COO−). The porphyrin free-base conjugates were studied with Na+, Ca2+, Zn2+, Cd2+, Pb2+, Fe2+, Ba2+, Cu2+, Ag+, and Hg2+, showing a colorimetric effect (color change from purple to yellow) and an unprecedented selectivity for Hg2+. The insertion of coumarin moiety confers an unusual solubility of these conjugates in ethanol. One of the porphyrin free-base conjugate was fully studied in a mixture EtOH/H2O (50:50) and showed a similar behavior with Hg2+. Under these conditions, the conjugate presented a higher association constant than in toluene and was able to detect and quantify a minimal amount of 0.6 ppm and 1.2 ppm of Hg2+, respectively. Having in mind the biological and environmental application of these conjugates, non-expensive solid supports, like agarose and natural cellulose polymers were developed. In the cellulose support material (filter paper) the colorimetric effect for Hg2+ reveals a similar behavior as in solution. In addition pH studies carried out with the same conjugate showed a green color at low pH and a yellow color at high pH values in solution and in solid supports. [Display omitted]