A. A. Isakova

The crucial role of self-assembly in nonlinear optical properties of polymeric composites based on crown-substituted ruthenium phthalocyaninate†

Ruthenium(II) tetra-15-crown-5-phthalocyaninate with axially coordinated molecules of pyrazine [(15C5)4Pc]Ru(pyz)2 (1) was synthesized from a carbonyl complex [(15C5)4Pc]Ru(CO)(MeOH) (2), and the structure of the solvate complex (1)·6CHCl3 was revealed using the single crystal X-ray diffraction method. Analysis of the crystal packing showed that the weak intermolecular interactions, such as CH⋯π, CH⋯N, CH⋯O and CH⋯Cl, played an essential role in the formation of stable assemblies and their organization within the crystals. The interplay between the intramolecular axial coordinated pyrazine contacts and the weak intermolecular interactions of solvate molecules with crown-ether fragments provided the basis for rationalizing the observed self-assembly of molecules in solutions of tetrachloroethane and polymeric composites with polyvinylcarbazole. The self-assembly was investigated using UV-Vis spectroscopy, dynamic light scattering measurements, atomic force microscopy and transmission electron microscopy techniques. The formation of nanoparticles of complex (1) from a tetrachloroethane solution after three cycles of heating to 70 °C/cooling to 5 °C and two days storage was proved. Thin films (7 μm) of polymeric composites with polyvinylcarbazole prepared from a solution containing nanoparticles exhibited a nonlinear optical response measured by the Z-scan technique with application of femtosecond (1030 nm) and nanosecond (1064 nm) pulse lasers. The measured third-order susceptibility (χ(3)) of the polyvinylcarbazole composite with 4 wt% of complex (1) was equal to 1.94 × 10−10 esu, while the same composite prepared without the previously described special treatment had zero susceptibility. This result proves the essential role of self-assembly in future development of nonlinear optical materials.

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

The spectral and electrochemical properties of Langmuir-Blodgett (LB) films of homoleptic double-decker cerium bis-[tetra-15-crown-5]-phthalocyaninate Ce[R4Pc]2 and its heteroleptic analog [Pc]Ce[R4Pc] 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 phthalocyanine 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 investigations. 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, consequently, 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 molecules 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.

Nonlinear optical properties of systems based on (tetra-15-crown-5-phthalocyaninato)indium(III)

The nonlinear optical properties of solutions of (2,3,9,10,16,17,23,24-tetra-15-crown-5-phthalocyaninato)indium(III) [(15C5)4Pc]In(OH) in tetrachloroethane (TCE) have been studied by the z-scan method. It has been found that a nonlinear optical response is due to supramolecular associates formed in a tetrachloroethane solution by heating to 90°C/slow cooling to room temperature cycling. The formation of the supramolecular associates has been studied by atomic force microscopy (AFM) and electronic absorption spectroscopy (EAS). It has been shown that a single thermal treatment of [(15C5)4Pc]In(OH) solutions in TCE results in the predominant formation of dimers, as evidenced by both a short-wavelength shift of the Q-absorption band of the monomeric complex (λmax = 692 nm) to the band of λmax = 653 nm and height doubling of molecular entities as measured by AFM. The dimers are responsible for the two-photon absorption measured in the femtosecond range, which has a relatively high cross section of σ2 = 1.38 × 10−46 cm4 s/(molecule, photon) or 1.38 × 104 GM. According to the AFM data, three cycles of heat treatment of the solution leads to the formation of supramolecular assemblies of about 200 nm length. The optical spectrum exhibits long-wavelength absorption at λmax = 841 nm and the long-wavelength edge near 1300 nm. In the case of nanosecond 1064-nm laser irradiation, the linear absorption S0 → S1 is primary, having the cross section of σ0 = α0/N = 2.3 × 10−20 cm2. The known high quantum yield (close to unity) of triplet states of indium phthalocyanines suggests that the main nonlinear optical effect is determined by intersystem crossing S1 → T1 and triplet-triplet absorption T1 → T2. The absorption cross section is σT-T = 1.14 × 10−19 cm2.

Electrochemical synthesis and spectroelectrochemical properties of nanostructured polyaniline layers in the presence of various polyamidosulfonic acids

Electrochemical matrix polymerization of nanostructured polyaniline layers in the presence of polyamidosulfonic acids differing in the rigidity of the polymer framework was studied in a wide concentration range. The spectroscopic, electrochemical, and morphological properties of the resulting layers were examined. It was found that the accelerated electropolymerization is due to (1) preliminary association of aniline with the sulfo groups of the polyacids and (2) a high local concentration of the protons near its macromolecule. The use of a polyacid with a rigid polymer framework afforded an interpolymer complex with polyaniline in side chains. With a semirigid matrix, both a two-strand complex (characteristic of an acid matrix with a flexible chain) and a branched complex were obtained.

Peculiarities of polyaniline matrix synthesis in the presence of mixtures of different types of matrices and investigation of properties of formed interpolymer complexes

In the present work, the existence of a matrix domination effect in the formation process in polyaniline interpolymer complex solutions under aniline oxidation in the presence of rigid and flexible poly(amidosulfonic acid)s was demonstrated for the first time.

Effect of polymer sulfoacids with varying chain rigidity on the nucleation of their interpolymer complexes with polyaniline during electropolymerization on highly orientated pyrolytic graphite

The nucleation of the solid phase of interpolymer complexes of polyaniline (PAn) during electropolymerization of aniline on highly orientated pyrolytic graphite in aqueous solutions of hydrochloric acid and polymer sulfoacids, which differ in the rigidity of the polymer framework, was studied in situ by atomic force microscopy. The rigidity of the polyacid chain, which determines possible changes in its conformation in solution and its ability to adapt its conformation to that of the rigid conjugated PAn macromolecule, directly affects the shape and growth rate of the nuclei of solid phase of PAn and the film morphology at the early stages of electropolymerization. The rigid-chain and semirigid-chain polymer acids, which have the conformation of an elongated or slightly bent rod in solution, determine the conformation of the interpolymer complex nuclei. In contrast, in the presence of flexible-chain polyacids, the process is mainly controlled by the conformation of PAn macromolecules.

The effect of nanodiamond surface modification on interaction with Pseudomonas putida K12

Interactions between nanodiamonds with an unmodified surface and nanodiamonds with chlorinated, as well as aminated, surfaces and the bacterium surfaces and Pseudomonas putida K12 were studied. It was revealed that only nanodiamonds with a modified surface possessed a considerable biocidal effect. Aminated nanodiamonds were twice as efficient as chlorinated ones. Electron microscopy showed that nanodiamonds were adsorbed onto the cell surface and damaged it. It is proposed that the higher biocidity of the aminated nanoparticles was caused by a positive charge inducing electrostatic interaction with the negatively charged surface of the bacterial cytoplasmic membrane.

The influence of the surface structure of polyaniline films on the adsorption of influenza A viruses and antibodies to them

Adsorption of influenza A viruses and their antibodies on golden surfaces, thin films of polyaniline and polyaniline complex with polysulfonic acids, has been studied. The composition of interpolymer complexes was found to influence both the surface relief of synthesized films and the adsorption efficiency. Moreover, it has been shown that the adsorption of bio-objects increased with a growth of surface roughness of the polymer coatings. It has been suggested that this effect was caused by an tight contact between the studied bioobjects and the surface relief elements of close size. In addition, the surface protuberances can act as active centers of adsorption due to their larger accessibility. The results testify to the potential of application of films composed of interpolymer polyaniline complexes with a developed surface relief as a basis to prepare biosensors that are sensitive to viruses and antibodies.