Long-Sought Redox Isomerization of the Europium(III/II) Complex Achieved by Molecular Reorientation at the Interface

Langmuir 36(6), 1423 - 1429 (2020). doi:10.1021/acs.langmuir.9b03403
Redox isomerism, that is, the change of a metal cation valence state in organic complexes, can find promising applications in multistable molecular switches for various molecular electronic devices. However, despite a large number of studies devoted to such processes in organic complexes of multivalent lanthanides, redox-isomeric transformations were never observed for europium. In the present work, we demonstrate the unique case of redox isomerization of Eu(III)/Eu(II) complexes on the example of Eu double-decker octa-n-butoxyph- thalocyaninate (Eu[(BuO)8Pc]2) under ambient conditions (air and room temperature). It is shown that assumption of the face-on orientation on the aqueous subphase surface, in which two of each phthalocyanine decks in Eu[(BuO)8Pc]2 are located in different media (air and water), leads to the intramolecular electron transfer that results in the formation of a divalent Eu(II) cation in the complex. Lateral compression of the thus-formed monolayer results in the reorientation of bisphthalocyaninate to the edge-on state, in which the ligands can be considered identical, and occurrence of the reverse redox-isomeric transformation into the complex with a trivalent Eu cation. Both redox-isomeric states were directly observed by X-ray absorption near-edge structure spectroscopy in ultrathin films formed under different conditions.
Published by ACS Publ., Washington, DC