V. V. Shelkovnikov

Polymer films of J-aggregated cyanine dyes and metal clusters for non-linear optical applications

A new medium with non-linear optical properties, comprising J-aggregates of cyanine dyes entrapped in a polymer matrix is reported. Pseudoisocyanine and benzothiazolium dyes with C2H5 and C18H37 chains were synthesized; Langmuir–Blodgett and polymer films of these dyes were prepared. The temperature stability of the J-aggregates in films was investigated by optical spectroscopy. J-Aggregates in polymer films display a higher thermal stability than those in Langmuir–Blodgett films and can be used in non-linear susceptibility experiments. The cubic susceptibility of the films was measured by four-wave mixing and found to be 0.8 × 10–7 cm3 erg–1 for the degenerate case. Upon addition of metal clusters to the J-aggregate–polymer composite, an increase by a factor of >30 in the susceptibility was observed.

Nanometer films of polymethine dyes in optical memory and nonlinear optics

We present a review of experimental investigations in the synthesis and characterization of thin solid films of polymethine dyes in monomer and aggregate forms, which have been performed at the Institute of Organic Chemistry and the Institute of Automation and Electrometry (Siberian Branch of the Russian Academy of Sciences, Novosibirsk) for the past 15 years. The films, obtained by spin-coating technique on glass substrates, were intended for use in optical memory disks of the WORM (write once read many) type and as nonlinear optical media with cubic nonlinearity. The synthesized symmetric thioflavylium dyes with tert-butyl substituents form non-crystallized films of optical quality, which are suited for the creation of recording layers of WORM disks. Thermal, optical, and nonlinear optical properties of thin films based on J-aggregates of pseudoisocyanine derivatives with long alkyl substituents, the films of such dyes doped with cluster anions of higher boron hydrides, and the films of an aggregated thiocarbocyanine dye are considered. Nanometer films of stable J-aggregates of pseudoisocyanine derivatives exhibit the absolute values of the cubic optical nonlinear susceptibility on the order of 10−5 esu at room temperature and 10−4 esu at liquid nitrogen temperature. Thin films of J-aggregates of organic dyes can also be used as saturable absorbers of laser radiation.

Optical Properties of Solid Pseudoisocyanine Films Doped with Cluster Derivatives of Boron Hydrides

The formation and optical properties of J aggregates of pseudoisocyanine iodide in solid films in the presence of cluster anionic derivatives of boron hydrides and carboranes (B10H102-, B12H122-, B20H182-, [NiIV(1,2-B9C2H11)2]0, 1,2-B9C2H12-, [Co(1,2-B9C2H11)2]-, [Ni(1,2-B9C2H11)2]-, B10H8I22-, [Sn(1,2-B9C2H11)]0) are studied. It is shown that the addition of anions B10H102- or B10H8I22- leads to an efficient formation of stable J aggregates. The addition of carborane complex of nickel [NiIV (1,2-B9C2H11)2]0 also leads to the formation of J aggregates, although less stable ones. Carborane complex of tin [SnII(1,2-B9C2H11)]0 facilitates the formation of a monomeric form of the dye. The remaining compounds yield no distinct pattern of formation of a certain monomeric or J-aggregated film structure. With the aid of the semiempirical AM1 method, the charge distributions in the cation of the dye and anionic derivatives of the boron hydrides are calculated. It is supposed that the bipolar distribution of a negative charge in the B10H102- anion facilitates the formation of a J aggregate. By addition of salts of organic cations to a film of pseudoisocyanine-closo-hydrodecaborate (PCG), J aggregates with a narrow width of the J peak are obtained. The thermal decay of J aggregates in these films is studied. On the basis of the data obtained (the presence of an isosbestic point upon thermal decomposition of J aggregates and their reaggregation; the narrowing and increasing of the J absorption peak, as well as increasing of luminescence, upon dilution of a J-aggregated PCG film with organic cations; and the bipolar character of the electrostatic interaction of the B10H102- anion with the dye), it is assumed that the J peak of pseudoisocyanine in the films studied corresponds to the absorption of a dimeric form of the dye.

Dynamics of pulsed recording of holographic diffraction gratings in photopolymer materials

The dynamics of recording holographic diffraction gratings in photopolymer material using 10-ns pulses of Nd:YAG laser radiation (532 nm) was investigated. The formation of permanent and intermediate gratings was observed. Optimization of the photopolymer composition for pulsed recording was performed. The kinetic photopolymerization models taking into account the mechanisms of radical destruction due to recombination and by impurities are verified. Measurement of the recording kinetics at different recording angles showed that diffusion does not affect the hologram formation for times of the same order of magnitude as the recording duration (0.1 s) at a length of the grating half-period. Samples of the photopolymer composition in triethanolamine were investigated and diffusion of oligomeric acrylamide molecules was revealed. The diffusivity was found to be 1.1 × 10−9 cm2/s.

J-aggregates of pseudoisocyanine with long alkyl substituents in thin films: Synthesis, spectral properties, and thermal stability

The formation and properties of J-aggregates in thin solid films of pseudoisocyanines with long N-alkyl groups, obtained by centrifuging from solutions in organic solvents, were studied. It is shown for the first time that nonsymmetric cyanine dyes, containing a C2H5 group at one nitrogen atom and a C10H21, C15H31, or C18H37 group at another nitrogen atom, spontaneously form J-aggregates stable at room temperature and pressing a narrow absorption band with a half-width at half maximum of 200 cm−1. The thermal stability of J-aggregates in thin films of pseudoisocyanines with alkyl substituents decreases in the following order: C2H5-C2H5> C2H5-C6H13>C2H5-C18H37>C2H5-C10H21>C2H5-C15H31. By introducing 1-octadecyl-2-methylquinolinium iodide in the film, it was found that the J-aggregates studied consist of a small number (2–4) of dye molecules.

Improved Synthesis of Thiofluorescein

Thiofluorescein was synthesized in a preparative yield by successive demethylation of 3,3′-dimethoxydiphenyl sulfide to 3,3′-dihydroxydiphenyl sulfide and condensation of the latter with phthalic anhydride in H2SO4. The title compound was also obtained in a higher yield from 3,3′-dimethoxydiphenyl sulfide directly in a one-pot process combining the condensation in H2SO4 and demethylation in 2 Py · H2SO4.

Optical and Nonlinear-Optical Properties of Pseudoisocyanine J-Aggregates with the Controlled Exciton Absorption Linewidth

Thin films of molecular J-aggregates of pseudoisocyanine with different linewidths of exciton absorption (from 75 to 210 cm–1) were obtained. A change in the absorption linewidth of J-aggregates was achieved by introducing organic salts into a sample. As an alternative method of varying the exciton absorption linewidth, variation in sample temperature was used. For the samples obtained, the third-order nonlinear optical susceptibility χ(3) was measured at temperatures of 80 and 293 K by the Z scan and pump–probe spectroscopy techniques and the dependence of χ(3) on the absorption linewidth W was found to follow a power law. It was revealed that the character of the function χ(3)(W) is almost independent of the method for measuring the absorption linewidth to have the form χ(3) ∼ Wδ with δ ≈ –(1.36–1.58). Based on this finding, the relation of the exciton delocalization length in the aggregate to the absorption linewidth and optical nonlinearity is discussed.

Luminescent silica nanoparticles modified with a functional pyrylocyanine dye

A method was developed for the chemical modification of silica nanoparticles with a pyrylium dye under the sol-gel synthesis conditions. The films of silica particles modified with a pyrylium dye gave greenish blue luminescence with a maximum at 490 nm upon treatment with a solution of butylamine. The film samples of silica nanoparticles modified with pyrylocyanine exhibited good light resistance.

Optical constants of nanofilms of J aggregates of organic dyes, measured by spectral ellipsometry and polarization reflectometry

The dispersion of the complex refractive index of thin films of J aggregates of organic dyes has been measured by spectral ellipsometry and polarization reflectometry. It is found that almost all films of J aggregates exhibit normal dispersion in the long-wavelength region, where the films are transparent. In the spectral range where the films absorb, anomalous dispersion is observed with a maximum in the J peak. The refractive index n in this range becomes as high as ≃2.5–3.5. It is revealed that polarization reflectometry provides adequate accuracy in determining the optical constants n and κ of nanofilms of organic dyes.

Method for determining the shrinkage parameters of holographic photopolymer materials

A method has been developed to determine the shrinkage parameters of holographic photopolymer materials (including changes in the mean refractive index and thickness of the recording layer) during hologram recording with a measurement error acceptable for practical applications of these materials. Experimental verification of the method has proved its efficiency.