Infrared photorefractive composites based on polyvinylcarbazole and carbon nanotubes

Photorefractive materials based on unplasticized polymers that have a high glass-transition temperature and the frozen random orientation of chromophores were prepared by layer casting. Under these conditions, only the third-order susceptibility has a nonzero value, increasing with an increase in the conjugation-chain length and reaching considerable values in the case of nanosized molecules, such as single-wall carbon nanotubes (SWNTs). In SWNT-containing polyvinylcarbazole, the photoelectric sensitivity and photorefractive characteristics were measured at 1064 nm. Using electric-field induced second-harmonic generation, the third-order susceptibility was estimated. In a composite containing 0.26 wt % SWNT, the diffraction grating is displaced by 5° relative to the interference pattern, the result that is presumably due to the close mobility of unlike charge carriers. Therefore, the beam-coupling gain coefficient Γ and the net gain Γ-α have low values, which are 53 and 42 cm^?1, respectively, at 115 V/μm.     

Photorefractive polymer composites for the IR region based on carbon nanotubes

The photorefractive properties of polymer composites based on aromatic polyimide and single-wall carbon nanotubes are studied using radiation at a wavelength of 1064 nm. It is found that the nanotubes possess photoelectric sensitivity in this spectral region and that the kinetic photorefractive characteristics of the polymer composites are entirely determined by the photogeneration and charge transport characteristics of the layers. The two-beam gain coefficient of the signal beam measured for a composite consisting of aromatic polyimide and 0.25 wt % of single-wall carbon nanotubes in a constant electric field E₀ = 79 V/μm is equal to 84 cm^?1 and exceeds the optical absorption coefficient by 59 cm^?1. The refractive index modulation is equal to Δn = 0.004 at E₀ = 54 V/μm.     

The influence of a solvent on the aggregation of ruthenium(II) tetra-15-crown-5-phthalocyaninate

The images of ensembles of ruthenium(II) complexes with tetra-15-crown-5-phthalocyanine and axially coordinated triethylenediamine molecules, (R₄Pc)Ru(TED)₂, obtained on an atomic force microscope were analyzed. A comparison with the X-ray structure analysis data was performed to estimate the number and mutual arrangement (architecture) of molecules in supramolecular aggregates depending on the nature of the solvent and the temperature of solutions before casting. Storage at room temperature or heating of a solution of the complex in tetrachloroethane caused the formation of stable supramolecular “wires” 600 nm or more long. The z-scanning method was used to study the third-order nonlinear optical characteristics of solutions of the (R₄Pc)Ru(TED)₂ complex in tetrachloroethane.     

Carbon nanotube-containing photorefractive polymer composites operating at telecommunication wavelengths

The field dependences of photocurrent, the two-beam coupling gain coefficient, and the grating formation time constant in polymer composites made from polyvinylcarbazole (PVK) and single-wall carbon nanotubes (SWNTs) were measured under the conditions of one-photon SWNT excitation with continuous laser radiation at a wavelength of 1550 nm. Carbon nanotubes are responsible for optical electronic absorption up to ～2000 nm in this composite. The dependence of the quantum efficiency of generation of mobile charge carriers on the electric field E ₀ as determined from the photocurrent coincides with the curves calculated via the Onsager equation expanded to the (E ₀)⁴ term, at a quantum yield of thermalized electron-hole pairs of η₀ = 0.07 and a charge separation distance in the pair of r ₀ = 9.8 Å. An analysis of the photorefractive characteristics showed that the admixture of fullerene C₆₀ in an amount of 3 wt % to the PVK composite with 0.26 wt % SWNT leads to a twofold increase in the beam-coupling gain coefficient. In the PVK-matrix composite containing 0.26 wt % SWNT and 3 wt % C₆₀, the beam-coupling gain coefficient Γ of a 1550-nm laser beam and the net gain Γ-α are 32 and ～27 cm^?1, respectively, at a constant field of E ₀ = 140 V/μm.     

A walk around the A3-coupling

In recent years, the transition-metal catalyzed three-component coupling of an aldehyde, an alkyne and an amine, commonly called A(3)-coupling, has been established as a convenient and general approach towards propargylamines. Furthermore, the A(3)-coupling has found a broad application as a key step in the construction of various nitrogen-containing heterocycles, biologically active compounds and natural products. Several interesting modifications of the A(3)-coupling as well as different tandem reactions involving A(3)-coupling have been developed. This tutorial review aims to highlight the current achievements in the field of A(3)-couplings and related transformations.     

Photorefractive Properties of Photochemically Modified Poly(hydroxyaminoether)

The exposure of photosensitive poly(hydroxyaminoether)-based polymer compositions to light leads to the formation of an image with nonlinear optical and photoelectric properties and, hence, photorefractive behavior. Using the holographic birefringence technique, it was shown that the pumping of one of laser beams (signal beam) at the expense of the intensity of another (reference beam) takes place in the photochemically modified regions of the polymer layer. Unlike the majority of the previously studied photorefractive polymeric media, the beam-coupling gain coefficient (cm^–1) exceeds the absorption coefficient (cm^–1); i.e., the intensity of the signal beam after passing the layer becomes higher than that before the layer. A net internal gain, i.e. the difference – , of 117 cm^–1is achieved at E ₀= 26 V/m. The photorefractive effect is absent from the unexposed areas of the layer.     

Photorefractive Composites Based on Nanocrystalline Carbocyanine Dye J-Aggregates with a Fast Response Time

The use of carbocyanine dye J-aggregates as sensitizers of photoelectric sensitivity and chromophores with the third-order nonlinear optical polarizability made it possible, by the action of two intersecting He–Ne laser (633 nm) beams and an applied electric field, to obtain photorefractive spatial modulation of the refractive index in a nonplasticized polymer layer having the glass transition temperature of about 230°C with a short (20 ms) time of response to this action. A fairly high two-beam-coupling gain coefficient was obtained, which reached a value of = 218 cm^–1 at an applied field of E ₀ = 50 V/m. The net internal gain (difference between the beam-coupling gain coefficient and the absorption coefficient ) was – = 143 cm^–1 under these conditions.     

Differentiating alkyne reactivity in the post-Ugi transformations: Access to polycyclic indole-fused frameworks

The Ugi adducts prepared from propiolic acids, propargylamines, indole-2-carbaldehydes, and isocyanides were utilized to assemble polycyclic indole-fused frameworks via two consecutive carbocyclizations involving triple bonds. First, the peptidyl position of Ugi adduct underwent potassium carbonate-mediated cyclization onto the triple bond derived from propiolic acid. Then, the position 3 of indole core engaged into gold-catalyzed cyclization onto the propargylamine-originated alkyne, completing the construction of polycyclic core.     

Tetrasubstituted 2-imidazolones via Ag(I)-catalyzed cycloisomerization of propargylic ureas

A one-pot protocol based on a Ag(I)-catalyzed cycloisomerization of propargylic ureas, derived from secondary propargylamines and isocyanates, was developed for the generation of the 2-imidazolone core.