Electrochemically controlled multistability of ultrathin films of double-decker cerium phthalocyaninates

Abstract

The spectral and electrochemical properties of Langmuir-Blodgett (LB) films of homoleptic double decker cerium bis [tetra 15 crown 5] phthalocyaninate Ce [R 4 Pc] 2 and its heteroleptic analog [Pc]Ce[R 4 Pc] were studied. It was shown that during formation of Langmuir monolayers upon contact of both complexes solutions with water subphase the metal center with valent state IV in the solution transforms into one with the valent state III in the monolayer. Upon cyclic compression expansion of these monolayers, orientation induced reversible intramolecular transfers of electron from 4f orbital of cerium ion to the phth alocyanine macrocycle (compression) and in reverse direction (expansion) occur in a planar supramolecular system. Scheme of reversible electrochemical transformations occurring in ultrathin films of double decker cerium crown phthalocyaninates, one of which is associated with the Ce +3 /Ce +4 redox transition of metal center of the complex, was proposed and substantiated using the results of spectro electrochemical investi gations. It was shown that one of these transformations is associated with the Ce +3 /Ce +4 redox transition of metal center of the complex and upon change of metal center oxidation state its size changes, and, conse quently, the distance between the decks of the complex also changes. This change in the distance can lead to a substantial (13-15%) modulation of the linear size of molecular assemblies with a large number of mole cules in stack. On the basis of this effect the supramolecular device that can perform mechanical work can be developed. Using surface plasmon resonance technique we have demonstrated that a step change in electrode potential in region of 200-1000 mV induces a corresponding optical response reflected in a step change of the resonance angle. High operation speed and reversibility of switching between stable states can serve as a basis for development of optoelectronic switching systems.

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.…”

“…The existence of the dynamic equilibrium between sandwich complexes of tri-and tetravalent cerium in solutions should be noted. [23] The measurements of electrochemical properties of solutions and Langmuir-Blodgett films (LBF) carried out by cyclic voltammetry method have shown that in full accordance to literature data, [31,32] voltammograms of doubledecker complexes of trivalent lanthanides contain two peaks in the range of potentials from -0.5 to 1.0 V, one of which (in the area of 0.3−0.6 V) can be assigned to the process of oneelectron oxidation of the phthalocyanine ligand, and another one (in the range of -0.13-0.00 V) − to its one-electron reduction ( Figure 2, curve 1). At the same time, CV curve of 15-crown-5 substituted double-decker complexes of cerium, which can change its valence state in such complexes, exhibits three peaks in the same range of potentials ( Figure 2, curve 2), one of which, apparently, corresponds to the redox process on the metal center cation.…”

“…One of such factors is the presence of oxidizers, and, primarily, atmospheric oxygen. Previously, [23] we have proposed that reduction of lanthanide bis-phthalocyaninates in ultrathin films in the presence of dissolved oxygen occurs in a multi-stage manner, and only the first, electrochemical stage of this process, takes place at the redox-transition, observed on the voltammogram.…”

“…[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.…”

Conjugated compounds in supramolecular informational systems: A review

“…Since then, molecular systems that exhibit bista bility-the ability to exist in two different electronic states and change their electronic state upon the effect of external actions-have attracted especial attention of researchers. The continuing interest in processes of reversible intramolecular electron transfer exists because these processes appear promising as a basis for develop ment of molecular sensors and nanosized devices for recording and storage of information [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42].…”