Electrochemistry of a Double-Decker Lutetium(III) Phthalocyanine in Aqueous Media. The First Evidence for Five Reductions

Abstract

The double-decker lutetium(III) phthalocyanine, Lu[(RS)4Pc]2, where R = C12H25, was synthesized and electrochemically characterized under several solution conditions. The neutral complex undergoes a single reversible one-electron oxidation and up to four reversible one-electron reductions in nonaqueous solutions of CH2Cl2 or benzonitrile containing 0.1 M tetra-n-butylammonium perchlorate (TBAP), while one oxidation and five reductions are seen in aqueous 0.5 M KCl for a gel-like cast film membrane of Lu[(RS)4Pc]2 in a tetraoctylphosphonium bromide (4C8P+Br-) matrix at a basal plane pyrolytic graphite electrode. The half-wave potentials for reduction of Lu[(RS)4Pc]2 in CH2Cl2, 0.1 M TBAP are located at E 1/2 = 0.04, −1.03, −1.36 and −1.73 V, while the single oxidation is located at E 1/2 = 0.43 V vs SCE. These potentials, when measured vs Fc/Fc+, are negatively shifted by 0.20−0.46 V from the E 1/2 values obtained in the 0.5 M KCl solution where the electrogenerated anions of the double-decker complex are stabilized by the cations of the 4C8P+Br- matrix and five reductions are seen at E 1/2 = 0.29, −0.66, −0.94, −1.22, and −1.41 V vs SCE. The fifth reduction has been theoretically predicted but had never before been observed for any double-decker lutetium(III) phthalocyanine or related complex. A cast film of Lu[(RS)4Pc]2 displays only one oxidation in the 0.5 M KCl solution (at E 1/2 = 0.78 V vs SCE), and no reductions at all are seen in the absence of a matrix. An almost identical oxidation potential of E 1/2 = 0.80 V is seen for oxidation of Lu[(RS)4Pc]2 in KCl when dissolved in the cationic matrix. These half-wave potentials for oxidation in the cationic film, when measured vs Fc/Fc+, are thus more positive by more than 0.27−0.32 V than E 1/2 values measured in CH2Cl2 or PhCN and this is consistent with a decreased degree of solvent or anion binding to {Lu[(RS)4Pc]2}+ in the 4C8P+Br- matrix, as compared to what is observed in solution.

Ultrafast photo-induced charge transfer unveiled by two-dimensional electronic spectroscopy

“…14 The resulting high degree of charge carrier mobility readily explains their semiconductivity 15,16 and electrochromic behavior. 17,18 In its electronic ground state, lutetium bisphthalocyanine ([LuPc 2 ]) is a stable radical ([LuPc 2 ]…”

Comparative Electrochemical Study of Unsubstituted and Substituted Bis(phthalocyaninato) Rare Earth(III) Complexes

“…[12b,15] The same methodology has been applied here to render possible the first observation by DPV of the fifth one-electron reduction of M(Pc) 2 in solution. [15] Results and Discussion The electrochemical behavior of all the double-decker sandwich complexes M(Pc) 2 was first investigated by cyclic voltammetry (CV) and then differential pulse voltammetry (DPV) in CH 2 Cl 2 . The half-wave redox potentials vs. SCE are summarized in Table 2.…”

Three new vic‐dioxime ligands: Synthesis, characterization, spectroscopy, and redox properties of their mononuclear nickel(II) complexes

“…Direct proportionality of the cathodic peak current with the scan rate provides evidence for the adsorption character of reduction wave [31]. The anodic or cathodic peak potentials of the complexes could be expected to shift by the introduction of electron-donating or electron-withdrawing groups on the oxime moity as previously observed for phthlocyanine complexes [32][33][34][35][36]. However, the experimental results showed that no introduction of the electron-donating phenyl groups on the oxime moity for [Ni(L 2 H) 2 …”