Tuning of the photophysical and electrochemical properties of ruthenium(II) phthalocyaninates by variation of axial ligands

Abstract

A series of mononuclear ruthenium(II) tetra-tert-butyl-phthalocyaninates bearing axial N-donor ligands [tBu₄PcRu]L₂ (L = trimethylamine, pyrazine, 4,4′-bipyridine and N-methyl-4,4′-bipyridinium iodide) as well as the binuclear complex [tBu4PcRu]₂(BiPy)₃ were synthesized starting from the complex with axially coordinated carbonyl group [tBu₄PcRu](CO). All compounds have been characterized by NMR, UV-Vis and cyclic voltammetry. The latter allowed the determination of oxidation and reduction potentials, HOMO-LUMO gaps and revealed the possibility of electropolymerization of BiPy-containing complexes in clear contrast to complexes containing another bidentate ligand – pyrazine. Comparative electrochemical studies of the mono- and binuclear complexes [tBu₄PcRu](BiPy)₂ and [tBu₄PcRu]₂(BiPy)₃ revealed that the phthalocyanine rings are not conjugated in the binuclear species. The remarkable dependence of singlet oxygen generation from axial ligands in ruthenium phthalocyaninates was observed: the complexes with carbonyl group [tBu₄PcRu](CO) and with pyrazine molecules [tBu₄PcRu](Pyz)₂ show higher ¹O₂ quantum yields, whereas the complex with axially coordinated molecules of trimethylamine [tBu₄PcRu](NMe₃)₂ and quaternized BiPy ligands [tBu₄PcRu](BiPy-Me⁺)₂ have the lowest ability to generate singlet oxygen. The revealed influence of axial ligands on key physicochemical properties paves the way for the design of new ruthenium phthalocyaninates with potential optoelectronic and biomedical applications.

Keywords:

• Ruthenium
• phthalocyanine
• axial ligand replacement
• electrochemistry
• singlet oxygen generation

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The syntheses and photophysical studies of ruthenium phthalocyaninates were supported by the Council for Grants of the President of the Russian Federation for state support to young Russian scientists (grant SP-4189.2021.1). The electrochemical studies of ruthenium complexes were supported by the Russian Science Foundation (grant No. 23-73-00037). NMR and MALDI-TOF measurements were performed using equipment of CKP FMI IPCE RAS and IGIC RAS.