In situ monitoring of metallation of metal-free phthalocyanineviaUV-Vis and steady-state fluorescence techniques. Thin-layer UV-Vis and fluorescence spectroelectrochemistry of a new non-aggregating and electrochromic manganese(3+) phthalocyanine

Abstract

A new non-aggregating and electrochromic manganese(3+) phthalocyanine, (acetato)[2(3),9(10),16(17),23(24)-tetrakis(4-(1-naphthoxy-4-sulfonic acid sodium salt))phthalocyaninato]manganese(3+) [NhtMn(3+)PcL] (where Nht and L indicate naphthoxy-4-sulfonic acid sodium salt and acetate ion, respectively), was synthesized by reaction of the metal-free phthalocyanine (NhtH₂Pc) and manganese(2+) acetate (Mn(OAc)₂) in methanol. The formation of the complex was monitored by both in situUV-Vis and fluorescence techniques based on the change of the symmetry and the quenching of the fluorescence-probe molecule as a result of the insertion of the metal into the cavity of the macrocycle. The electro-spectrochemical behavior of [NhtMn(3+)PcL] was investigated with thin-layer UV-Vis and fluorescence spectroelectrochemical methods in DMSO solution. The electrochemical studies revealed that [NhtMn(3+)PcL] exhibited two reversible one-electron reductions which were assigned to Mn(2+)Pc(2–)/Mn(3+)Pc(2–) and Mn(2+)Pc(3–)/Mn(2+)Pc(2–) reversible couples based on the metal and phthalocyanine ring reductions, respectively. All redox processes were accompanied with a change of color from dark green to green and purple which are clearly monitored on the surface of the light transparent platinum gauze working electrode in the thin-layer cell. In situUV-Vis and fluorescence spectroelectrochemical methods were also applied to determine the E_1/2 (half-wave potential) and n (number of electrons) of the first reduction process, both of which confirmed the reversible one-electron [Mn(3+)Pc(2–)L] + e → [Mn(2+)Pc(2–)L]^–reduction process.