Redox-controlled multistability of double-decker cerium tetra-(15-crown-5)-phthalocyaninate ultrathin films

Abstract

The optical and electrochemical properties of novel double-decker cerium bis-tetra-15-crown-5-phthalocyaninate [ Ce ( R 4 Pc 2−)2]0 (R4Pc2− = [4,5,4',5',4",5",4'",5'"-tetrakis-(1,4,7,10,13-pentaoxapentadecamethylene)-phthalocyaninate-anion]) Langmuir-Blodgett and cast films were investigated. The particular feature of cerium ion in complex with tetra-15-crown-5-phthalocyanine is the stability of oxidation state +4 unlike other lanthanide metal centers. Cyclic voltammetry curves exhibited three stable redox states in the Langmuir-Blodgett and cast films. Redox processes in Langmuir-Blodgett films are reversible and reproducible at multiple scan procedures. The mechanisms of redox transformations in Langmuir-Blodgett films are suggested. We demonstrated that the well-defined structure of Langmuir-Blodgett film is essential for fast electron transfer within the planar system, in which the charge is delocalized along the conjugated assembly of uniformly ordered stacks of discotic crown-phthalocyaninate. Fast charge relaxation was observed in highly ordered Langmuir-Blodgett film whereas the electrochemically written redox states remained unchanged in unordered cast film. The combination of electrochemistry with surface plasmon resonance spectroscopy allowed us to demonstrate that stepwise change of potential in the range 200-850 mV induced the respective optical response, which can be observed as the change in resonance angle value. High-speed response and reversibility of the switching process between stable states may be utilized as the basis for switchable optoelectronic devices. Electrochemical multistability of cerium crown-phthalocyaninate provided a basis for developing a simple strategy to fabricate nanoelectromechanical systems with high efficiency and fast response. Our approach relies on the modulation of the distance between decks in a complex stack via redox-controlled change of metal center size that results in change of linear dimensions of the stacks. The reported results are valuable, not only because of their potential applications, for instance, in OFET and MEMS fabrication, but also from a fundamental point of view since they illustrate the interplay between the orientation of stacks bearing discotic aromatic molecules and charge transfer within such a planar assembly.

Orientation-Induced Redox Isomerism in Planar Supramolecular Systems

“…15,34,35 Unusual physicochemical and electrochemical properties of cerium bis [tetra (15 crown 5) phthalocyaninate] (Ce [(15C5) 4 Pc] 2 ; Figure 1) in comparison with other rare earth element complexes have been described recently in solution, Langmuir monolayers and Langmuir−Blodgett (LB) films. 34,36 In particular, changes in the UV−visible spectra of Ce [(15C5) 4 Pc] 2 monolayers that can be hypothetically attributed to IET were observed. 37,38 Nevertheless, theoretical under pinning and experimental proofs are not available to confirm this hypothesis.…”

(24-Сrown-8)-Linked Dimeric Phthalocyanines and Their Metal Complexes

“…[7][8][9][10][11][12][13][14] The stability of metal complexes with these classes of ligands allows to mention them as promising molecules for the development of novel homogeneous catalysts [15][16][17][18][19] as well as efficient receptors and sensors. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] The dimeric phthalocyanines, linked by rigid or labile linker are in the scope of modern research. [8,10] The origin of the linker, its geometry and rigidity allows development of ditopic molecules with particular arrangement of phthalocyanine fragments -linear, angular or cofacial.…”

Behaviour of Low-Symmetry Crown-Phthalocyanine in Solution: Concentration Aggregation vs. Cation-Induced Assembly

“…Since architecture of these assemblies affects their physical-chemical properties, this approach can be used to obtain supramolecular materials with desired functional characteristics. [5][6][7] Another approach to functionalized phthalocyanines implies synthesis of low-symmetry molecules, composed of different isoindole fragments. [8][9][10] Such molecules can be used as molecular blocks of supramolecular assemblies [11][12][13] and components of nonlinear optical devices and materials.…”