Orientation-induced redox transformations in Langmuir monolayers of double-decker cerium bis[tetra-(15-crown-5)-phthalocyaninate] and multistability of its Langmuir-Blodgett films

Abstract

The spectral, electrochemical, and optical properties of Langmuir-Blodgett films (LBFs) and cast films from a solution of new double decker cerium bis[tetra (15 crown 5) phthalocyaninate] (Ce(R 4 Pc) 2 ) are studied. Based on analysis of compression isotherms and quantum chemical calculations, schemes of the organization of Ce(R 4 Pc) 2 molecules at different states of its monolayers are proposed. Cor relation dependences are determined in order to relate the optical and electrochemical characteristics of monolayers and LBFs of sandwich type lanthanide phthalocyaninates to the ionic radii of their metal centers. The valent state of Ce ions in a monolayer forming complex is determined, and a sequence of redox trans formations occurring in LBF uppon appliance of a potential is proposed, one of the transformations being associated with the Ce 3+ /Ce 4+ redox transition. Orientation induced intramolecular electron transfer is revealed in the planar supramolecular system. It is shown that, during the formation of a monolayer from a Ce(R 4 Pc) 2 solution, a tetravalent metal center passes to a trivalent state. Monolayer compression to a high surface pressure reverts the complex to the electronic state typical of the solution. The reversible transforma tions observed upon the monolayer compression result from intramolecular electron transfer from the 4f orbital of Ce to the phthalocyanine ring and backwards. The high operation rate and the reversibility of switching between the stable states, which are determined by means of the surface plasmon resonance tech nique, upon a stepwise change in the electrode potential within the range of 200-850 mV may underlie the development of optoelectronic systems. With a large number of molecules in a stacking aggregate, changes in the distance between the decks of the complex that occur with changes in the oxidation level of the metal cen ter can substantially modulate the sizes of molecular ensembles. A supramolecular device capable of perform ing mechanical work can be developed based on this effect.

Orientation-Induced Redox Isomerism in Planar Supramolecular Systems

“…It was found that no analogous spectral changes occur upon spreading and compression of monolayers of these complexes, that is in conformity with the fact that these lanthanide ions can only exhibit a 3+ oxidation state in these complexes. 26,38 Spectra of monolayer of unsubstituted CePc 2 , in which Ce 4+ state is much more stable than in crown substituted complex, 7,15,34 also do not undergo such alterations upon deposition and compression and do not possess the band at about 500 nm ( Figure 6, curve 1). At last, the positions of bands at about 500 nm in DRAS of trivalent lanthanide complexes at the air−water interface recorded at 5 mN m −1 surface pressure ( Figure 6, curves 2− 6) are linearly correlated with corresponding ionic radii ( Figure 7).…”

The Role of Oxygen in Electrochemical Reduction of Double-Decker Phthalocyaninates of Lanthanides

“…As it is known, [17][18][19][21][22][23][24][25][26] cerium atom in sandwich-type phthalocyaninates can exhibit two oxidation states: +3, as all the lanthanides and +4. Special stability of the configuration of the 4f 0 free shell makes tetravalent state of the cerium ion quite stable.…”

“…[14][15][16][17][18] In this light, phthalocyaninates of lanthanides with variable valence attract great interest due to possibility of realization of additional redox-process associated with change of metal center oxidation state. [18][19][20][21][22][23][24][25] On the other hand, practical application of such compounds requires knowledge on the influence of external factors on properties of redox-processes taking place in these systems. One of such factors is the presence of oxidizers, and, primarily, atmospheric oxygen.…”

Design and evaluation of sensory systems based on amphiphilic anthraquinones molecular receptors

“…they take an «edge-on» orientation as a consequence of the stabilizing π-π stacking interactions. Evidently, low monolayer area values are recorded in such situations, which correspond precisely to such an orientation of the aromatic molecules [31][32][33][34][35]. In contrast, "face-on" orientation of anthraquinone moiety is preserved even at a high surface density of monolayer.…”