G. I. Nosova

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.

Synthesis and photophysical properties of soluble polyimides and polyquinazolones containing side-chain chalcones or azo chromophores

Soluble aromatic and carboxyl- and hydroxyl-containing polyimides, mixed polyimides, and polyquinazolones of various chemical structures, as well as a series of new dicyanoazobenzene chromophores, are synthesized. From 20 to 80 mol % of chromophore groups are incorporated into side chains of the polymers. The thermal, photosensitive, and nonlinear optical properties (second-harmonic generation) of the chromophore-containing polymers are investigated. The polymers with covalently attached groups of the dye DR-13 or azo-derivatives of 4-phthalonitrile demonstrate the highest nonlinearity. The T g values of the polyimides vary from 165 to 215°C; their temperatures corresponding to 5% weight loss lie in the range 290–350°C; and the measured coefficients of second-harmonic generation, d 33, for a number of polarized films based on chromophore-containing polymers attain several tens of picometers per volt. The incorporation of chromophore groups into the side chains of the polymers causes an increase in the photosensitivity of polyimides by an order of magnitude relative to that of the parent polymers (S 0.1 = (3−4) × 105 cm2/J in the range of dye absorption).

Synthesis and photo- and electroluminescent properties of copolyfluorenes with nile red fragments in side chains

New copolyfluorenes containing units of 4,7-dibromo-2,1,3-benzothiadiazole (green luminophore) and 3,6- or 2,7-dibromocarbazole derivatives with side-chain fragments of green (4-pyrrolidinyl-1,8-naphthalimide) and red (Nile red) luminophores and additional carbazole or diphenyloxadiazole groups are synthesized via the Suzuki copolycondensation reaction. The structure of the polymers is modified via insertion of triphenylamine, aryloxadiazole, and quinoxaline units in the backbone of copolyfluorenes and via introduction of triphenylamine, fluorene, and benzene terminal groups. The molecular-weight characteristics of the polycondensation products and the specific features of the transfer of polyfluorene emission energy to the indicated luminophores in solutions and films are studied. Coating the emissive copolyfluorene layer with electron-conducting and hole-blocking layers of poly[9,9-bis(6′-diethoxyphosphorylhexyl)fluorene] makes it possible to increase the brightness of light-emitting diodes (to 2380–3900 cd/m2) and their current and luminance efficiencies.

Temperature dependence and the dispersion of nonlinear optical properties of chromophore-containing polyimide thin films

Detailed investigations of the quadratic nonlinear response of a series of new polyimides with covalently attached chromophore DR13 are performed by the Maker fringes method in the range of fundamental wavelength from 850 to 1450 nm. Polymer films with thickness of 100–400 nm were spin-coated on glass substrates and corona poled. For these materials, the maximum values of the second harmonic generation coefficients d33 are 80–120 pm/V. A red shift of the nonlinear response dispersion with respect to the linear absorption spectrum was observed for the DR13 chromophore. The temperature dependences of linear absorption and nonlinear coefficients d33 for studied structures are observed. It was found that the temperature changes of the absorption spectra lead to appreciable contribution to the value of the nonlinear coefficient d33. The demonstrated high temperature stability (up to 120 °C) of chromophore-containing polyimide thin films makes it possible to eliminate the degradation of their nonlinear optical ...

Synthesis and electrooptical properties of triphenylamine- and oxadiazole-containing polymers

Soluble aromatic polyimides and copolyimides are synthesized on the basis of 4,4′-diaminotriphenylamine and oxadiazole-containing diamines. Poly(ester oxadiazoles) are prepared from acid dichlorides or oxadiazole-containing acid dihydrazides. The optical, electrochemical, and thermal properties of the polymers are investigated. It is shown that oxadiazole-containing polyimides and poly(ester oxadiazoles) are able to transfer electrons, while triphenylamine-containing polyimides and copolyimides can transfer holes and electrons.

Nonlinear optical properties of chromophore-containing polyimides with covalently attached dyes

Spectral dependences of quadratic nonlinear coefficients of new chromophore-containing polyimides with covalently attached DR13 chromophore molecules are synthesized and studied by the second-harmonic generation method in the fundamental radiation wavelength from 800 to 1400 nm. The obtained record values of quadratic nonlinear coefficients are 80 to 120 pm/V. Dispersions of refractive indices and extinction coefficients in the spectral range from 400 to 800 nm are determined by spectral ellipsometry, resulting in the improved accuracy of nonlinear coefficients..

Molecular mobility in comb-shaped copoly(methacrylates) with fluoromethylene and chromophore-containing side chains

The molecular mobility of copoly(methacrylates) with chromophore-containing side groups of various structures has been studied by the dielectric method. The region of relaxation of dipole polarization related to the segmental mobility (α process) has been discovered. At temperatures that are ∼30°C higher than those corresponding to the α process, the relaxation transition reflecting the reorientation of chromophore-containing side groups (δ process) takes place. It is suggested that the occurrence of the δ process is a general phenomenon for such systems. This effect allows one to determine the temperature at which the polarization of polymer films under application of corona discharge should be carried out so that a high level of nonlinear optical properties associated with the macroscopic noncentrosymmetrical orientation of chromophores may be achieved.

Light-sensitive chalcone-containing poly(amido imides)

Soluble poly(amido imides) and copoly(amido imides) containing main-and side-chain chromophore chalcone groups have been synthesized. Thermo-and photocrosslinking of polymer chains in films under UV irradiation have been studied. The mechanical properties, dielectric behavior, and photosensitivity and photoconductivity characteristics of the polymers have been investigated.

Molecular mobility of a comb-shaped copolymethacrylate with chalcone chromophore-containing side groups

The molecular mobility of copolymethacrylate with chromophore-containing chalcone side chains is studied by broadband dielectric spectroscopy. Five regions of dipolar polarization relaxation are identified: namely, γ, β, β1, α, and δ processes. It is shown that γ and β1 processes are related to the local mobility of methylene sequences and ester groups adjoining the backbone, while the α process is associated with the cooperative segmental mobility of the backbone. The β and δ processes are attributed to the mobility of chalcone groups: the local mobility in the glassy state (reorientation relative to the long axis of chromophores) and the cooperative mobility in the rubbery state (reorientation relative to the short axis of chromophores), respectively. The incorporation of 20% chalcone groups does not change the glass-transition temperature but enhances the cooperativity of the α process and intermolecular interactions.

Photosensitivity of polyimides and polyquinazolones based on aromatic and heteroaromatic diamines

Soluble polyimides containing triphenylamine residues as substituents at the imide nitrogen atom and polyquinazolones with diphenyl oxide, diphenylpropane, benzimidazole, benzoxazole, benzothiazole, oxadiazole, and triphenylamine moieties in the diamine component of the repeating unit have been synthesized. The spectroscopic study of polyquinazolones indicates their capability for donor-acceptor interactions. Emission bands of the polymers are of the exciplex nature. The photogeneration of current carriers in the polymers under study has been examined by the method of surface potential photoinduced decay. It has been shown that the intrinsic photosenitivity of polyquinazolones is nearly the same as (or somewhat higher than) that of the corresponding polyimides, but the former polymers are characterized by a less efficient spectral sensitization by dyes and donor-acceptor additives.