Investigation of solvent and electrolyte anion dependency on the Co(II)/Co(III) versus Pc(2-/Pc(1-) oxidation preference in <i>tert</i> -butyl substituted cobalt phthalocyanine by electrochemical and spectroelectrochemical methods

Cyclic voltammetry (CV), differential pulse voltammetry (DPV), and spectroelectrochemistry were used to explore the complex solvent- and electrolyte-dependent redox behaviour of tetra(tert-butyl)phthalocyaninecobalt(II) (Pc[Formula: see text](2[Formula: see text]Co(II)). Pyridine (Py), dichloromethane (DCM), and [Formula: see text]-dichlorobenzene ([Formula: see text]-DCB) were used as solvents, and tetrabutylammonium ([TBA]) [TBA](ClO[Formula: see text], [TBA](BF[Formula: see text], [TBA](PF[Formula: see text], [TBA]Br, and [TBA](B(C 6 F[Formula: see text], were used as electrolytes. We have demonstrated that the first reduction always reflects the Co(II)/Co(I) process. For the first oxidation, the Co(II)/Co(III) process was observed when Py was present, in DCM/[TBA](ClO[Formula: see text], and in DCM/[TBA]Br. In all other combinations, the Pc(2[Formula: see text]/Pc(1[Formula: see text] process was observed for the first oxidation. The first Pc(2[Formula: see text]/Pc(1[Formula: see text] oxidation process can be shifted entirely to the Co(II)/Co(III) oxidation in DCM/[TBA](PF[Formula: see text] using just 0.5% of Py, highlighting the role of axial coordination on oxidation site preference. Independent of the first oxidation, the second oxidation process leads to the formation of [Pc[Formula: see text](1[Formula: see text]Co(III)][Formula: see text], as confirmed by spectroelectrochemical experiments. These studies highlight the importance of selecting suitable electrolytes and solvents for the broader applications of transition metal phthalocyanines.