Orientation-Induced Redox Isomerism in Planar Supramolecular Systems
Résumé
In this work, a previously undescribed phenomenon of orientation-induced redox isomerism in a Langmuir monolayer is revealed in the case of cerium bis-[tetra-(15-crown-5)-phthalocyaninate]-(Ce[(15C5)4Pc]2). It was established that intramolecular electron transfer (IET) from the electronic system of phthalocyanine to the 4f-orbital of cerium atom occurs upon spreading of a (Ce[(15C5)4Pc]2) chloroform solution onto the air?water interface (3D -> 2D IET). This process is related to the transformation of Ce4+ cation in the solution to Ce3+ in the monolayer. It was also found that reversible Ce3+ <-> Ce4+ IETs occur upon compression (π1 -> π2) and expansion (π2 -> π1) of monolayer (2Dπ1 <-> 2Dπ2 IET, π-surface pressure). The mechanism of genuine redox isomerism was confirmed by the results of in situ UV?vis spectral measurements performed on monolayers and Langmuir?Blodgett films, AFM, and XPS studies of Langmuir?Blodgett films transferred at different surface pressures. The understanding of this reversible IET mechanism is especially important due to possible applications of such redox-isomeric systems in the development of nanoscale multibit information storage devices.
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