Monolayers and Langmuir-Blodgett films of crown-substituted phthalocyanines

Abstract

Tetra 15 crown 5 phthalocyanine ligand and its ruthenium complex with axial CO and MeOH groups were synthesized. The properties of their monolayers and Langmuir-Blodgett films were studied. In the case of the ligand, monolayer films of molecular associates are formed. The compatibility of the ligand and stearic acid in a mixed binary monolayer was established. Stearic acid improves the ligand distribution over the water surface and results in the formation of monolayer associates immobilized in its matrix. The condensation effect of Na + cations on the mixed monolayers was found. The ruthenium complex (R 4 Pc)Ru(MeOH)(CO) forms stable true monolayers. The macrocycle planes in stacking are inclined relatively to the normal to the subphase surface by an angle of 25°. The Langmuir-Blodgett films of the complex were established to have redox peaks. A high electrochemical stability of the Langmuir-Blodgett films and a high electroactivity of phthalocyanine rings were demon strated. It was shown by impedance spectroscopy that the binding of Na + and К + ions by Langmuir-Blodgett films of the (R 4 Pc)Ru(MeOH)(CO) complex results in an increase in the impedance values in a region of medium frequencies by three and five times, respectively.Discotic compounds forming columnar structures in block and dispersions attract researchers´ attention due to a possibility of their assembling to form linear transport systems (channels) extended at a supramolecular level. Phthalocyanines are typical representatives of these com pounds. Significant interest in these objects is caused by their unique properties important from both theoretical and practical points of view. These are the lability of the electronic structure of a macrocycle, formation of com plexes with the most part of metals, easiness in introduc ing peripheral substituents and axial ligands of different nature, multistability, etc. 1,2 A possibility of self assem bling of phthalocyanines to form linear associates favors the creation of related functional supramolecular systems with a uniform orientation. In almost all cases, ultrathin films assembled by the Langmuir-Blodgett method con sist of phthalocyanine nanotubes, whose axes are parallel to the support surface. However, for many practical pur poses it seems important that axes of discotic columns would be arranged along a direction close to the normal or at a small angle to the normal. In this case, planes of phthalocyanine macrocycles would be parallel to the sup port. Such a molecular structure of a film should provide a more efficient transport over channels, for instance, when phthalocyanine is used as a mediator of electron transfer to an electrode in various, including enzymatic, reactions, in redox processes for developing chemical sen sors, in photoelectric devices, etc. However, this orienta tion has not been accomplished yet in Langmuir-Blodgett films (LBF), because it is difficult to obtain this orienta tion in LBF precursors (monolayers on the water surface) for several reasons: amphiphility is absent, ...

Spin Crossover in Nickel(II) Tetraphenylporphyrinate via Forced Axial Coordination at the Air/Water Interface

“…Considering the fact that CRPcRu(pyz) 2 bears two axial pyrazine ligands, which are quite hydrophilic, face-on orientation of the molecule is most likely. The observed discrepancy between the experimental molecular area and the theoretical one is commonly explained by hydrophilic and labile nature of the crown-ether moieties, which can be partially immersed into the aqueous subphase and/or deformed slightly in the monolayer [ 36 , 37 , 38 , 39 ].…”

Supramolecular Control of Photochemical and Electrochemical Properties of Two Oligothiophene Derivatives at the Air/Water Interface

“…Increasing the value of surface pressure up to 30 mN/m led to a blue shift of the spectrum, the band at 435 nm (spectrum at π = 0 mN/m in Figure ) passing to 415 nm (upper spectrum in Figure (a)). Such a shift is usually attributed to the formation of H aggregates. ,− Thus, the H-aggregate formation of I starts upon spreading of the compound on the water surface and is completed by increasing pressure up to 30 mN/m. Interestingly, the release of surface pressure causes the recovery of spectral position of the long-wavelength band.…”

Two-Dimensional Aggregation of Crown-Phthalocyanine Ligand at Air-Water Interface

“…Besides, even use of solutions free of aggregates can lead to formation of aggregates on subphase surface, as was shown by us previously. [20] Thus, in present work, we developed the way to form true monolayers of H 2 R 4 Pc ligand at the air/ water interface using extremely diluted solutions of studied substance for monolayer formation. First step of our work was to study aggregation behavior of this compound in solutions.…”

“…In our previous work [20] we used so-called "spreaders", amphiphilic compounds that form stable monolayers at air/water interface, to improve the distribution of crownsubstituted phthalocyanine ligand over water subphase. But this method introduces new substance into the monolayer, and could lead to interaction between spreader and studied compound, decrease effective amount of columnar structures on the working surfaces and change optical behavior of LB films obtained from such mixed monolayer.…”