Multifunctional Porphyrin-based dyes for cations detection in solution and thermoresponsive low-cost materials

Two β-pyrrolic substituted porphyrinic dyes 3 and 4, have been synthesized and fully characterized. Both compounds showed spectral alterations upon metal interaction indicating the complexation of the inner nitrogens in the porphyrin moiety by the metal ion. Their sensing ability towards the divalent and monovalent, Zn²⁺, Cd²⁺, Co²⁺, Fe²⁺, Ni²⁺, Cu²⁺, Ag⁺ and Hg²⁺ metal ions was evaluated in solution by absorption and fluorescence spectroscopy. The association constants, minimal detectable and quantified amounts for all metal ions were also determined. The results reveal the formation of mononuclear species in all cases, with the best results obtained for the toxic Hg²⁺ metal ion, where the lowest detectable and quantified amounts of 0.9/5.3 μM and 1.8/3.6 μM were observed for compounds 3 and 4, respectively. Polymeric films of poly(methylmethacrylate) (PMMA) doped with porphyrins 3 and 4 were also prepared and tested in the presence of the aforementioned metal ions and at different temperatures. For comparison, polymeric films of PMMA containing the non-substituted porphyrin 5,10,15,20-tetraphenylporphyrin (TPP) and with its Zn(II) complex (ZnTPP) were also tested at different temperatures. The temperature assays using the PMMA_3 and PMMA_4 doped polymers showed an interesting recovery in the emission intensity of ca. 70–80% in the cooling phase (from 100 °C to 35 °C). The results suggest the potential of these porphyrin dyes to be used in the preparation of smart plastic labels with temperature sensing features.