Synthesis, electrochemical, and spectroelectrochemical properties of tetrakis(13,17-dioxa nonacosane-15-sulphanyl) phthalocyaninato zinc(II)

Tetrakis(13,17-dioxa nonacosane-15-sulphanyl) phthalocyaninato zinc(II), ZnPc(SCH(CH₂OR)₂)₄, where R = C ₁₂H₂₅, was synthesised and its electrochemical and spectroelectrochemical properties were investigated in dichloromethane. The neutral complex undergoes two quasi-reversible one-electron oxidations and two quasi-reversible one-electron reductions in CH₂Cl₂ containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). The half-wave potentials for oxidation of the complex are located at E_1/2 = 0.61 and 1.38 V, while the two reductions are located at E_1/2 = -0.87 and -1.11 V versus SCE. These potentials show little or no difference compared to those of unsubstituted ZnPc and other SR substituted phthalocyanines under the same experimental conditions, thus suggesting weak electron-donating effects of the peripheral alkylthio substituents on the phthalocyanine rings. The well-defined UV-Vis spectra of electro-reduced and electro-oxidised species, [ZnPc(-3)(SCH(CH₂OR)₂)₄]^-, [ZnPc(-4)(SCH(CH₂OR)₂)₄]^2- and [ZnPc(-1)(SCH(CH₂OR)₂)₄]⁺, were obtained by applied potentials (E_app = -1.04 V, E_app = -1.62 V, and E_app = 1.20 V, respectively) in a thin-layer cell. The first and second reduction products showed characteristic spectral changes corresponding to mono- and di-anionic species of zinc phthalocyanines, and the first oxidation showed spectral changes corresponding to the formation of a mono-cationic dimer.