RU2242782C2 - Light-refracting polymeric material - Google Patents

Abstract

FIELD: polymer materials.

SUBSTANCE: invention provides light-refracting polymeric material with high diffraction efficiency in the near infrared region that can be used in optoelectronic devices, in processes of real-time recording of dynamic holograms, and in other photon technologies. Mixture according to invention is made from composition containing (i) 90.0-99.8% of polymer with high vitrification temperature selected from: dielectric polymer, semiconductor polymer devoid of system of conjugated double bonds in its main chain or semiconductor polymer having system of conjugated double bonds in its main chain and (ii) 0.20-10.0% of cyanine or squaryl dye in the form of J-aggregates as sensitizer and nonlinear optic chromophore.

EFFECT: extended spectral range for sensitivity of material in the near infrared region, in particular light-refracting and physico-mechanical properties, and increased hologram recording speed.

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Description

The invention relates to photorefractive polymeric materials with high diffraction efficiency in the near infrared region of the electromagnetic spectrum and can be used in optoelectronic devices, in the process of recording dynamic holograms in real time, amplification of information laser beams, fiber optic communication, image transmission through electromagnetic radiation scattering media, optical transmission of light scattering biological tissues and other photonic technologies.

Polymer photorefractive materials are known [1] (US Patent, 5,744,267, class G 03 H 001/04; G 03 C 001/72, 1998), which contain, wt%: semiconductor polymer polyvinylcarbazole 33, ethyl or methyl plasticizer -, or phenylcarbazole 16, an optical sensitizer 2,4,7-trinitrofluorenone 1, nonlinear optical (UFO) azo dye 50. These materials have a maximum laser beam gain of two-beam interaction G = 220 cm ^-1 in an electric field E = 90 V / μm at a wavelength of electromagnetic radiation λ = 675 nm. Hologram recording time is 10 s.

A disadvantage of the known polymer photorefractive materials is a narrow spectral range of sensitivity, limited on the side of long waves by red light with λ = 675 nm. In addition, high G values are provided by the low glass transition temperature of the photorefractive polymer material and, accordingly, by the high mobility of UFOs of chromophore molecules. A low glass transition temperature is achieved by the introduction of a high concentration of low molecular weight plasticizer. In this case, the physicomechanical characteristics of the polymer layer sharply worsen: it becomes plastic and experiences irreversible deformations over time, in addition, the molecular mobility in the layer sharply increases. This leads to diffusion and agglomeration of the sensitizer molecules, which significantly impairs the stability of the photorefractive characteristics of the layer. Since the recording speed of a hologram is determined by the slow process of orientation of the chromophore molecules in an electric field, it is low and amounts to 10 s.

Closest to the proposed composition and properties is a polymer photorefractive material containing a semiconductor polymer polyvinylcarbazole, which provides hole transport, ethylcarbazole as a plasticizer, (2,4,7-trinitro-9-fluoronilidene) malononitrile as an optical sensitizer, which ensures the sensitivity of the material to the near infrared region of electromagnetic radiation λ = 830 nm and a UFO chromophore from a number of polyene molecules in monomolecular form [2] (Science. 1998, v. 279, p. 54). Polyene molecules have a large dipole moment, polarizability anisotropy and hyperpolarizability, which ensures a high value of an important parameter of a photorefractive material - a large dynamic range (modulation of the refractive index Δn), the maximum value of Δn is 1.5 × 10 ^-3 at λ = 830 nm. Using the formula Г = 4πΔnsinψ / λ, we can estimate the maximum value of the laser beam gain in a two-beam interaction Г (max.), Which is realized when the phase is shifted between phase and interference gratings ψ = π / 2, Г (max.) = 225 cm ^-1 . The photorefractive effect in this material is a consequence of two factors:

1) in a strong constant external electric field at a low glass transition temperature, the UFO molecules of the chromophore are oriented in the field direction, macroscopic noncentrosymmetry arises and, as a result, a noticeable second-order susceptibility χ ² , with modulation of the refractive index Δn due to the electro-optical Pockels effect;

2) the internal modulated space charge field causes adequate modulation of the orientation of the dipole chromophores and birefringence, which leads to an additional increase in Δn. In addition, the recording speed of holograms is low, since it is determined mainly by the slow process of orientation of the chromophore molecules in an electric field and is equal to 6 s.

The disadvantage of the prototype is the limitation of photorefractive sensitivity with a boundary wavelength of 830 nm, determined by the long-wavelength optical absorption band of the spectral sensitizer. In addition, high modulation of the refractive index Δn is ensured by the low glass transition temperature of the photorefractive polymer material and, accordingly, the high mobility of the UFOs of the chromophore molecules. A low glass transition temperature is achieved by the introduction of a high concentration of low molecular weight plasticizer. In this case, the physicomechanical characteristics of the polymer layer sharply worsen: it becomes plastic and experiences irreversible deformations over time, in addition, the molecular mobility in the layer sharply increases. This leads to diffusion and agglomeration of the sensitizer molecules, which significantly impairs the stability of the photorefractive characteristics of the layer.

The invention solves the problem of expanding the spectral sensitivity range of a photorefractive polymer material in the long wavelength region of the infrared range of electromagnetic radiation while significantly improving its photorefractive and physico-mechanical properties and increasing the speed of hologram recording.

The problem is solved in that the photorefractive polymer material contains a polymer with a high glass transition temperature from the following series: dielectric polymer, for example, polymethyl methacrylate Dacryl-2M, Dacryl-8, Dacryl-87; Dacryl 81; Dacryl-82, Dacryl KAU, or a semiconductor polymer without a conjugated double bond system in the main chain, for example, aromatic polyimide based on 9,10-bis (m-aminophenylthio) anthracene and 1,3-bis (3,4-dicarboxyphenoxy) benzene and based on 9,10-bis (m-aminophenylthio) anthracene and 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] propane or a semiconductor polymer with a system of conjugated double bonds in the main chain, for example, polyphenylene vinyl , poly [2-cyano, 5- (2'-ethyl-hexyloxy) paraphenylene-vinylene], poly [2-butyl, 5- (2'-ethyl-hexyloxy) paraphenylene-vinylene] and cy an anine or squarilium dye in the form of J-aggregates in the following ratio of components (wt.%): polymer 90-00.8, dye 0.2-10.

As is known, J-aggregates are nanocrystalline particles having a linear size from 5 to 100 nm and are usually formed in aqueous solutions of dyes [3] (J-aggregates / Ed.T. Kobayashi. - World Scientific, Singapore, 1966). Since the wavelengths of electromagnetic radiation in the visible and near infrared regions of the spectrum are more than an order of magnitude larger than the sizes of J-aggregates, the introduction of the latter into an amorphous transparent polymer layer does not cause the scattering of light passing through the layer, and thus does not impair the spectral characteristics of the latter.

The choice of J-aggregates of cyanine dyes or squarilium dyes is due to the following reasons. Cyanine dyes, for example,

3,3’-di (γ-sulfopropyl) -9-ethyl-5,5’-dimethoxycarbocyanine pyridinium

3,3’-di (γ-sulfopropyl) -4,5,4 ’, 5’-dibenzo-12-methyl-11,13- (β, β-dimethyltrimethylene) -thiadicarbocyanine betaine triethylammonium,

3,3’-diethylthiacarbocyanine triethylammonium,

Triethylammonium 3,3’-diethyl-9-methylthiacarbocyanine,

5,5’-dichloro-3,3’-diethyl-9-ethylthia-carbocyanine pyridinium,

2,4-bis (1,3,3-trimethyl-2-indolinylidenemethyl) -1,3-dithiosquariilium dye,

2,4-bis (1,3,3-trimethyl-2-indolinylidenemethyl) -1,3-dithiosquariilium dye,

The 2,4-bis (1,3,3-trimethyl-2-indolinylidenemethyl) -1,3-diphenylsquarilium dye has an absorption depending on the structure from blue to near infrared. Their J-aggregates are nanocrystalline particles and absorb electromagnetic radiation 100-300 nm longer than the absorption of monomer molecules of the corresponding dye. Thus, in principle, the long-wavelength limit may exceed 1550 nm. In addition, J-aggregates form a centrosymmetric structure in the preparation of photorefractive polymer material, which has an extremely high susceptibility of the third order x ⁽³⁾ . Therefore, the orientation of the J-aggregates in the electric field, which is a necessary operation in the prototype, is not required, and the modulation of the refractive index Δn is determined by the electro-optical Kerr effect in proportion to Ex ⁽³⁾ . As a result, there is no need to use polymers with a low glass transition temperature. In this work, we used the previously developed method for the formation of J-aggregates of dyes in the polymer layer [4] (High Molecular Compounds - 2000, Series A, v. 42, No. 2, p. 299), in which the polymer and dye are several times in a suitable liquid solvent gradually heated to 60 ° C and slowly cooled to 20 ° C. As a result of several heating-cooling cycles of the solution, the dye from the monomolecular form passes into the form of nanocrystalline J-aggregates.

It is known that to obtain a photorefractive effect, photogeneration of charge carriers and their transport from illuminated regions to unlit regions of photorefractive material are necessary. In the prototype, the charge generator is a sensitizer. In the proposed photorefractive polymer material, the J-aggregates are the photogenerator, which simultaneously perform the functions of UFO chromophores. In addition, J-aggregates taken in high concentrations also act as transport centers and, therefore, dielectric polymers (e.g. polymethylmethacrylate) can be used as a polymer. At low concentrations of J-aggregates, the transfer of charge carriers is carried out through transport centers included in the main chain of the polymer macromolecule (e.g. polyphenylene vinyl aromatic polyimide), or associated with it as side substituents (e.g. polyvinylcarbazole). In any case, the proposed photorefractive polymer material consists of two components: a polymer matrix and J-aggregates of a cyanine dye or squarilium dye.

Example 1. A photorefractive polymeric material is obtained by dissolving in chloroform an aromatic polyimide based on 4-aminotriphenylamine and 3,4,3 ', 4'-tetracarbodiphenyl oxide (glass transition temperature ~ 230 ° C) and thiacarbocyanine dye 3,3'-di (γ- sulfopropyl) -9-ethyl-5,5'-dimethoxycarbocyanine pyridinium in the ratio of components, wt.%:

Polymer 99.8

Dye 0.2

The composition after double heating to 60 ° C and cooling to room temperature is applied in a centrifuge on a transparent electrically conductive film ITO (In ₂ O ₃ / SnO ₂ ), covering the glass substrate. After evaporation of the solvent on a glass substrate coated with ITO, a thin layer of photorefractive polymer material is formed. The layer thickness depending on the number of components taken ranged from 3 to 100 microns. Then, photorefractive holographic characteristics are measured on a holographic apparatus described in [5] (High Molecular Compounds - 2001, Series A, v. 43, No. 2, p. 977). The time constant for the formation of a dynamic hologram when recording a grating at a wavelength of 700 nm is 3 s, the refractive index changes 4.1 × 10 ^-3 , and the laser beam gain is G = 399 cm ^-1 in an electric field E = 120 V / μm. When the dye concentration is below 0.2 wt.%, The efficiency of the formation of J-aggregates decreases sharply and the dye remains mainly in a monomolecular form.

Example 2. A photorefractive polymer material is prepared by dissolving polyphenylene-vinylene-poly [2-methoxy, 5- (2'-ethyl-hexyloxy) paraphenylene-vinylene] and cyanine dye 3,3'-di (γ-sulfopropyl) -4 in tetrachloroethane. 5,4 ', 5'-dibenzo-12-methyl-11,13- (β, β-dimethyltrimethylene) -thiadicarbocyanine betaine triethylammonium in the ratio of components, wt.%:

Polymer 99.4

Dye 0.6

and process, as indicated in example 1. The time constant of the formation of a dynamic hologram when recording a grating at a wavelength of 830 nm is less than 20 ms, the change in refractive index is 3.3 × 10-3, the laser beam gain is G = 318 cm ^-1 in electric field E = 90 V / μm.

Example 3. Photorefractive polymer material is obtained by dissolving in tetrachloroethane aromatic polyimide and 2,4-bis (1,3,3-trimethyl-2-indolinylidenemethyl) -1,3-dithiosquarylium dye in the ratio of components, wt.%:

Polymer 96

Dye 4

and process as described in example 1.

The time constant for the formation of a dynamic hologram when recording a grating at a wavelength of 1064 nm is shorter than 20 ms, the change in the refractive index is 2.6 × 10 ^-3 , the gain of the laser beam is G = 24 cm ^-1 in an electric field E = 90 V / μm.

Example 4. Photorefractive polymer material is obtained by dissolving in acetone polymethylmethacrylate-dacryl 2M (glass transition temperature ~ 100 ° C) and 3,3'-diethylthiapentacarbocyaninide in the ratio of components, wt.%:

Polymer 90

Dye 10

and process as described in example 1.

The time constant of the formation of a dynamic hologram when recording a grating at a wavelength of 1550 nm for 5 s, a change in the refractive index of 5 × 10 ^-4 , the gain of the laser beam G = 220 cm ^-1 in an electric field E = 90 V / μm. When the dye concentration is above 10 wt.%, J-aggregates are combined into larger formations that scatter coherent laser radiation, resulting in a sharp drop in photorefractive characteristics.

Thus, the developed photorefractive polymer material has a combination of a large gain of laser beams in the infrared region of the spectrum from 700 to 1550 nm with a high recording speed of dynamic holograms, good photorefractive and physico-mechanical properties.

Claims (1)

A photorefractive polymer material made on the basis of a composition comprising a polymer, a sensitizer and a nonlinear optical chromophore, characterized in that a polymer with a high glass transition temperature is used, selected from: dielectric polymer, a semiconductor polymer without a conjugated double bond system in the main circuit, or a semiconductor polymer with a system of conjugated double bonds in the main chain, and as a sensitizer and nonlinear optical chromophore use cyanine or squarilium edge a carrier in the form of J-aggregates with a ratio of components, wt.%: Polymer 90.0-99.8 Dye 0.20-10.0