Orientation-Induced Redox Isomerism in Planar Supramolecular Systems

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)(4)Pc](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)(4)Pc](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 (pi(1) -> pi(2)) and expansion (pi(2) -> pi(1)) of monolayer (2D(pi 1) <-> 2D(pi 2) IET, pi-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.