Metallo-phthalocyanines bearing 5,7-dichloro-8-hydroxy-2-methylquinoline substituents: Synthesis, electrochemistry and spectroelectrochemistry

Abstract

In this work, 4-((5,7-dichloro-2-methylquinolin-8-yl)oxy)phthalonitrile (3) and peripherally tetra 5,7-dichloro-8‑hydroxy-2-methylquinoline substituted zinc(II) (4), nickel(II) (5), copper(II) (6), cobalt(II) (7) and manganese (III)chloride (8) phthalocyanines were prepared for the first time. Electrochemical characterizations of metallo-phthalocyanines were performed to determine their redox activities and influence of the metal centers and substituent to the redox responses. Peripherally tetra substituted zinc(II) (4), nickel(II) (5) and copper(II) (6) phthalocyanines illustrated very similar redox responses due to the redox inactivity of the Zn²⁺, Ni²⁺and Cu²⁺ central cations. Peripherally tetra substituted cobalt(II) (7) and manganese (III)chloride (8) phthalocyanines gave metal based electron transfer processes in addition to the phthalocyanine based ones. The reduction processes of cobalt(II) phthalocyanine (7) were assigned to [Co^IIPc^2-]/[Co^IPc^2-]^1-, [Co^IPc^2-]^1-/[Co^IPc^3-]^2- and [Co^IPc^3-]^2-/[Co^IPc^4-]^3-[Co^IIPc^2-]/[Co^IIIPc^2-]¹⁺couples and the oxidation processes were assigned to [Co^IIPc^2-]/[Co^IIIPc^2-]¹⁺and [Co^IIIPc^2-]¹⁺/[Co^IIIPc^1-]²⁺couples. For manganese (III) chloride (8), [Cl^1--Mn^IIIPc^2-]/[Cl^1--Mn^IIPc^2-]^1-, [Cl^1--Mn^IIPc^2-]^1-/[Cl^1--Mn^IPc^2-]^2-, [Cl^1--Mn^IPc^2-]^2-/[Cl^1--Mn^IPc^3-]^3- and [Cl^1--Mn^IPc^3-]^3-/[Cl^1--Mn^IPc^4-]^4- couples were recorded during the reduction process and [Cl^1--Mn^IIIPc^2-]/[Cl^1--Mn^IIIPc^1-]¹⁺couple was recorded during the oxidation process. Spectral changes observed during the in-situ spectroelectrochemical measurements supported these redox mechanisms. Multi-electron transfer processes and distinct color changes indicated possible usage of novel phthalocyanines in various electrochemical and opto-electrochemical processes.