A new water-soluble metal-free phthalocyanine substituted with naphthoxy-4-sulfonic acid sodium salt. Synthesis, aggregation, electrochemistry and in situ spectroelectrochemistry

A new water-soluble metal-free phthalocyanine, 2,9,16,23-tetrakis(4-(1-naphthoxy-4-sulfonic acid sodium salt))phthalocyanine NhtH2Pc, where Nht indicates naphthoxy-4-sulfonic acid sodium salt, was synthesized and its aggregation, electrochemical and spectroelectrochemical properties were investigated in non-aqueous solutions. The aggregation study of NhtH2Pc showed that NhtH2Pc had both aggregated and non-aggregated mono phthalocyanine forms in the case of the 1:1 ratio of methanol and water, while it exhibited only the characteristic UV–Vis absorption of monomeric phthalocyanine in methanol and DMSO. NhtH2Pc displayed three reversible one-electron reductions waves, assigned to Pc3−/Pc2−, Pc4−/Pc3− and Pc5−/Pc4− couples, respectively. The electrochemical half-wave potentials of the reduction processes were located at E1/2 = −0.510, −0.924 and −1.24 V, respectively while the anodic potential of the oxidation process was displayed at E1/2 = 0.590 V versus pseudo Ag/AgCl. The half-wave potentials of the first and second reductions were positively shifted by 0.150 and 0.136 V compared with those of the unsubstituted metal-free phthalocyanine (H2Pc). These shift values are almost the same as those observed for [(SO3)4H2Pc]. The electrochemical studies showed that the electron-withdrawing sulfonated-naphthoxy groups on the macrocycle core made the reduction processes of NhtH2Pc easier in DMSO solution. The well-defined UV–Vis spectra of the electro-reduced species [NhtH2Pc]− were obtained with an applied potential (Eapp = −0.70 V) in a thin-layer cell. The spectroelectrochemical results showed that the first reduction product exhibited characteristic spectral changes corresponding to mono-anionic species of metal-free phthalocyanines, having long-term stability during the reduction process.

A new water-soluble metal-free phthalocyanine, 2,9,16,23-tetrakis(4-(1-naphthoxy-4-sulfonic acid sodium salt))phthalocyanine NhtH2Pc, was synthesized and its electrochemical and spectroelectrochemical properties were investigated in DMSO solution. The aggregation study of NhtH2Pc shows that NhtH2Pc exhibits the characteristic monomeric UV–Vis absorption of phthalocyanine in methanol and DMSO. NhtH2Pc displays three reversible one-electron reductions waves assigned to Pc3−/Pc2−, Pc4−/Pc3− and Pc4−/Pc5− couples, respectively. The well-defined UV–Vis spectrum of the electro-reduced species [NhtH2Pc]− was obtained with an applied potential (Eapp = −0.70 V) in a thin-layer cell.Figure optionsDownload as PowerPoint slide