Redox behavior of unsubstituted cobalt phthalocyanine in nanostructured Langmuir-Schaefer films

Abstract

Although the properties of unsubstituted metal tetrapyrroles in solutions have received attention in numerous work, the physico-chemistry of their thin films remains poorly investigated. In this work, we constructed thin films of unsubstituted cobalt phthalocyanine on the surface of quartz plates and indium tin oxide (ITO) electrodes using the Langmuir-Schaefer (LS) and drop casting techniques. In LS films, CoPc species are involved in strong intermolecular interactions, which result in formation of CoPc nanostructures and prominent changes in the ultraviolet-visible spectrum. Electrochemical reduction of CoPc in LS films at −0.9 V (versus silver chloride electrode) results in formation of Co(I) species. In contrast to the highly reactive nature of Co(I)Pc in solution, these species generated in thin films are relatively resistant to dioxygen due to the dense packing of CoPc units. These findings can further the development of CoPc-based resistive sensors utilizing not only common Co(II), but also Co(I) species, which may possess different sensitivity toward analytes.

Keywords:

• Langmuir-Schaefer films
• nanostructures
• unsubstituted cobalt phthalocyanine
• redox properties

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the grant of the Russian Science Foundation (20-12-00175-p), Ivanovo State University of Chemistry and Technology (ISUCT, electrochemical properties study), and Ministry of Science and Higher Education of the Russian Federation (FZZW-2023-0009, film formation and spectral study). The authors acknowledge ISUCT (Ivanovo, Russia) for the resources provided by the center for shared use of scientific equipment (075-15-2021-671).