V. V. Kudryavtsev

Second-order nonlinear optical susceptibility in chalcone-group crystalline molecular compounds

A study is reported of the second-order nonlinear optical susceptibility in polycrystalline molecular materials of the chalcone group made by second-harmonic generation at a wavelength of 1.06 µm. Some of the compounds studied exhibit a high nonlinear activity and are transparent in the blue region of the spectrum. The measured macroscopic nonlinear polarizability χ2 was compared with the calculated values of β, the second-order molecular polarizability tensor. The high nonlinear optical polarizability observed in some chalcone compounds is shown to be related to crystal symmetry type.

Thermal desorption states of C60 fullerene molecules in polymer matrices

Polymer-C60 fullerene composite coatings are studied using thermal desorption mass spectrometry. It is found that thermal desorption spectra of C60 fullerene molecules can exhibit several resolved peaks (at a specified heating rate) corresponding to thermal desorption states. The relative intensity of the thermal desorption peaks depends on the procedure used for preparing the composite coatings, in particular, on the time of sedimentation of the polymer-fullerene suspension. The occurrence of different stages in thermally stimulated desorption of C60 fullerene molecules is explained by the fact that the fullerene molecules can exist in several phase states characterized by different densities and degrees of ordering in the polymer matrix.

Thermally stimulated desorption of C60 and C70 fullerenes from rigid-chain polyimide films

Polyimide-fullerene composite thin coatings are investigated using thermal desorption mass spectrometry in the temperature range 20–800°C. It is found that, at temperatures below the temperature of decom-position of the polymer matrix, thermally stimulated desorption of fullerene molecules is limited by the diffusion of fullerene molecules in the matrix. The diffusion coefficients and activation energies of diffusion of C60 and C70 fullerene molecules are determined from the experimental data on thermally stimulated desorption in the framework of several approaches. It is revealed that the diffusion of C70 molecules in the polyimide matrix is more hindered than the diffusion of C60 molecules in the same matrix.

Photoinduced Birefringence in Comblike Poly- n -(fluoroalkyl methacrylates) and Their Hydrocarbon Analogs with Nonlinear Optical Chromophores in Side Chains

Comblike polymers (copolymers) of methacrylates with nonlinear optical photochromic chromophores in the side chains are synthesized. An increase in the induced birefringence under laser radiation is studied in poly-n-(fluoroalkyl methacrylates) and their hydrocarbon analogs. It is demonstrated that the chemical structure and composition of polymers (copolymers) affect the rise and decay of the photoinduced birefringence and the stability of the second-harmonic generation signal.

Light sensitivity of photoconducting polymer systems with polymethine dyes based on derivatives of 2(4)-methylquinoline and indole

The photosensitivity of conducting polymer films with newly synthesized polymethine dyes is investigated. It is demonstrated that the photosensitivity of polymer films based on poly(o-hydroxyamide) with transport indole molecules forming intermolecular complexes with dyes is two or three times higher than the photosensitivity of the polymer films containing indole as a structural component of the dye. The introduction of the indole-containing dye into the photoconducting poly(vinylcarbazole) leads to an increase in the photo-conductivity by one and a half orders of magnitude. In this case, the quantum yield increases to η = 0.085. A correlation is revealed between the electronic structure of the dyes, the characteristics of the photoconduction in the materials under investigation, and the mechanisms of charge relaxation in the samples. An increase in the photoconductivity of the films results in the crossover from the drift mechanism of charge relaxation to the relaxation mechanism associated with intrinsic electrical conduction.

Dielectric relaxation in polymers and copolymers of methacrylates and methacrylamides with chromophoric groups in side chains

The dielectric relaxation and molecular motion in polymers and copolymers of methacrylates and methacrylamides with π-conjugated anisodiametric chromophoric groups in the side chains are investigated in the temperature range from −170 to 120–150°C at frequencies of 0.1–100 kHz. It is shown that the motion of chromophoric groups and relaxation transitions in these systems are similar to those in liquid-crystal polymers with side mesogenic chains. The chromophoric groups execute orientational motion of two types: orientational rotations about the long axes in the glass state and orientational rotations about the short axes at temperatures above Tg. The π-conjugation excludes local motion within the chromophoric group.

Third harmonic generation in copolymer films with optically nonlinear N-substituted 4-nitroazobenzene in the side and main polymer chains

The third-order nonlinear optical susceptibility χ(3)(3ω; ω, ω, ω) of two types of copolymer films containing optically nonlinear N-substituted nitroazobenzene in the side (methacrylic series copolymers) and main (copolyimidoamido esters) polymer chains is investigated using the third harmonic generation method at a wavelength of 1.064 µm.

Photosensitive comb-like copolymers with 2-(2-chloroaniline)-4,6-dimethylpyrimidine chromophore in side chain and their Langmuir–Blodgett films

Abstract New amphiphilic photosensitive three-component random copolymers of octafluoropentylmethacrylate (OFPM), methacrylic acid (MA) and o -chlorophenylpyrimidine containing chromophore 6-[ N -(4,6-dimethyl-2-pyrimidyl)- N -(2-chlorophenyl)amino]hexylmethacrylate or 2-( N -allyl-2-chloroaniline)-4,6-dimethylpyrimidine are described. By means of 1 H NMR and electron spectroscopy, it was found that the main photoreaction of these copolymers is cyclization with the participation of heterocycle nitrogen atom of o -chlorophenylpyrimidine chromophore resulting in its conversion into N -substituted pyrimido-[1,2- a ]-benzimidazolium chloride. Efficiency of charge carriers photogeneration in polymeric films of macroscopic thickness was determined with the method of photoinduced decay of surface potential. One of the copolymers was shown to form monomolecular layers on aqueous subphase and conditions for formation of Langmuir–Blodgett (LB) films were determined. Bilayer spacing of these films was evaluated from X-ray reflectivity data.

Effect of the processes of orientation of nonlinear optical fragments of a side chain in comb-shaped polymers of the methacrylic series on the second-harmonic generation in thin films

New comblike copolymers of methacrylic acid esters with an optically nonlinear chromophore—a derivative of the 4′-(4-nitrobenzylideneamino)phenol—in a side chain were obtained. Processes of forced orientation of nonlinear optical chromophores covalently bonded with the main chains in an electric field and the effects of the conditions of orientation on the nonlinear second-order optical activity of the polymer films were studied in some detail. The existence of a correlation between the chemical structure and the composition of the copolymers with the magnitude and the stability of the surface electron potential of the corresponding films was shown. It was established that a maximum extent of orientation of chromophores in the bulk of the polymer and, as a consequence, a high intensity of the second-harmonic signal were achieved when the thickness of the region of the uniform electric field maximally approached the thickness of the sample.

Current hysteresis in magnetic tunnel junctions

A current hysteresis is detected in magnetic tunnel junctions of the ferromagnetic metal-nonmagnetic insulator-ferromagnetic metal type. The hysteresis is manifested in the formation of loops on the curves describing the dependence of the current through the junction on the applied voltage, as well as in the nonreproducibility of this dependence. This effect is caused by the influence of the spin-polarized current on the magnetic state of metallic layers: the current leads to a rearrangement of the domain structure under these conditions.