Photoelectric, nonlinear optical, and photorefractive properties of polyvinylcarbazole composites with graphene

Polyvinylcarbazole (PVK) composites containing graphene in an amount of somewhat less than 0.15 wt % exhibit third-order dielectric susceptibility due to the presence of graphene, as well as photoelectric and photorefractive sensitivity at 1064 nm. The photorefractive (PR) effect is known to occur in a polymer composite that possesses both photoelectric sensitivity and nonlinear optical properties. The photoelectric, nonlinear optical, and PR properties of PVK composites with graphene have been considered in this paper.     

Photorefractive IR-spectrum composites prepared from polyimide and ruthenium(II) tetra-15-crown-5-phthalocyaninate with axially coordinated triethylenediamine molecules

It is established that supramolecular ensembles on the basis of the complex of ruthenium(II) with tetra-15-crown-5-phthalocyanine and axially coordinated triethylenediamine molecules (R₄Pc)Ru(TED)₂, where R₄Pc^2? and TED denote 4,5,4′,5′,4″,5″4?,5?-tetraksis-(1,4,7,10,13-pentaoxatridecamethylene)phthalocyaninate ion and triethylenediamine molecule, respectively) make an aromatic polyamide layer photoelectrically sensitive to 1064-nm Nd:YAG laser radiation, exhibit third-order susceptibility, and, consequently, impart photorefractive properties to the polymer layer at this wavelength.     

Nonlinear optical properties of polyvinylcarbazole composites with graphene

The study has focused on polyvinylcarbazole (PVK) composites with graphene. It has been shown that there is a noticeable nonadditive shoulder on the long-wavelength edge of the optical absorption of PVK in these samples, which can be attributed to the formation of a charge-transfer complex between PVK as a donor and graphene as an acceptor. The formation of the complex causes a significant nonlinear optical effect in the PVK/graphene composite. The revealed increase in both the nonlinearity coefficient with increasing laser intensity and the cross section with increasing incident energy density is due to the formation of the graphene^?· radical anion, an additional species contributing to nonlinear absorption, with an increase in the radiation energy density. Nonlinear optical properties of PVK composites with graphene isolated from a solution in tetrachloroethane after 1.5-h centrifugation (sample 1) have been considered. It has been suggested that a significant decrease in optical transmission of laser radiation by the composite T _OA = 0.4 at an energy density at focus of 502 J/cm² is due to the formation of the PVK/graphene charge-transfer complex responsible for the nonadditive shoulder on the long-wavelength optical absorption edge of PVK. During photoexcitation of graphene in the PVK/graphene composites at a laser wavelength of 1064 nm, mobile holes are generated in PVK, indicating the formation of graphene^?· radical anions as a result of charge transfer from PVK to photoexcited graphene. The observed increase in both β with an increase in the laser radiation intensity and the cross section (σ_exc — σ₀) with an increase in the incident energy density may be due to either the contribution of nonlinear transitions (S ₀ → S ₂, S ₀ → S ₁ → S ₂, T ₁ → T ₂) or the formation of the additional species, the graphene-· radical anions, participating in nonlinear absorption by increasing the energy density at the focus (F _foc, J/cm²).     

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 (λ_max = 692 nm) to the band of λ_max = 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 λ_max = 841 nm and the long-wavelength edge near 1300 nm. In the case of nanosecond 1064-nm laser irradiation, the linear absorption S ₀ → S ₁ 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 S ₁ → T ₁ and triplet-triplet absorption T ₁ → T ₂. The absorption cross section is σ _T-T = 1.14 × 10^?19 cm².     

Synthesis and photophysical properties of polyphenylquinoxalines with thiophene and dibenzothiophene units in the backbone

New bis(α-diketones) containing thiophene and dibenzothiophene groups were synthesized. Via the reaction of these monomers with aromatic tetramines under high-temperature polycondensation conditions, a series of new polyphenylquinoxalines combining high thermal and mechanical characteristics with solubility in organic solvents were prepared. Polyphenylquinoxalines exhibit intense fluorescence in solution and in thin films with maxima in the region of 432–522 and 450–530 nm in the case of thiophene-containing and dibenzothiophene derivatives, respectively.     

Transient electroluminescence and anomalous dispersion of charge carriers in thin polymer films

The electroluminescence and charge carrier transport in an organic light-emitting diode based on a thin polymer film are investigated. The initial kinetics of transient electroluminescence is analyzed theoretically. Both the theoretical and experimental curves are characterized by an anomalous dispersion and universality, which can be considered a consequence of the nonequilibrium field-assisted dispersion of charge carriers. It is demonstrated that the drift mobility of charge carriers should be determined from the time corresponding to the half-height of the steady-state electroluminescence intensity rather than from the delay time of the electroluminescence.     

Autocatalytic reactions in polymer films and solutions containing ferrocene and carbon tetrabromide

The effective rate constants of autocatalytic reactions taking place in the system Fc-CBr₄-aromatic amine are not decreased on passing from a liquid solution to a polymer film in the absence of oxygen. When films containing the above components are covered on both sides with poly(vinyl alcohol) their oxygen content is reduced to a level at which it has no effect on the autocatalytic reactions which produce colored products in the films.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 346–351, February, 1991.