Novel non-peripheral mercaptopyridine-substituted mono- and double-decker lutetium(iii) phthalocyanines: synthesis, photophysicochemical and electrochemical properties

Abstract

In this study, novel non-peripheral tetra-mercaptopyridine-substituted mono- and double-decker phthalocyanines (LuPc and LuPc₂) containing lutetium(III) as a rare earth metal were synthesized and characterized using different spectroscopic techniques. ESR and electrochemical analyses were performed to support the sandwich structure of LuPc₂. The g factor was determined to be 2.00039 and the characteristic first reduction couple at 0.29 V indicated a reduction of the radical Pc ring of LuPc₂. In addition, the UV-Vis-NIR spectra of LuPc₂ in neutral, reduced, and oxidized states demonstrate its intrinsic π-radical nature in CHCl₃. The photophysicochemical properties of LuPc and LuPc₂ were investigated in DMSO. It was found that mono-phthalocyanine (LuPc) is a more effective photosensitizer than double-decker (LuPc₂) and metal-free (H₂Pc) phthalocyanines based on a comparison of their photophysical and photochemical properties. The singlet oxygen quantum yields (Φ_Δ) of the synthesized LuPc and LuPc₂ compounds were calculated to be 0.57 and 0.14, respectively, and the obtained results were compared with H₂Pc (Φ_Δ = 0.04). Also, electrochemical measurements were performed to estimate their redox potentials and the results indicated the important electrochemical performance of double-decker phthalocyanine (LuPc₂).