Ternary inclusion complexes of cyclodextrins with spin-labeled indoles and hydrocarbons. The formation of 2: 1: 2 complexes and partial dissociation of spin-labeled guests in the presence of a hydrocarbon liquid phase

The interaction of ternary complexes γ-or β-cyclodextrin (CD)-spin-labeled indole (pyrrolidine (1) or piperidine (2) derivative)-hydrocarbon (benzene or cyclohexane) with the liquid phase of these hydrocarbons gives rise to a new type of complexes (s) the ESR spectra of which are indicative of a much lower rotational mobility and its weaker temperature dependence for the spin-labeled guests compared with the initial ternary complexes (w). The formation of s-complexes is accompanied by a decrease in the proportion of the initial w-complexes. This gives rise to several isosbestic points in the ESR spectra, which indicates the formation of s-complexes from w-complexes. The rotational diffusion coefficient of 2 in s-complexes decreases 6–10-fold with respect to its value for w-complexes and the libration amplitude of 1 in the s-complexes decreases to 5–6° at 295 K. Transition between the two types of complexes occurs with characteristic times of 10³–10⁵ s and is reversible: upon the removal of the hydrocarbon, the proportion of the strongly immobilized s-signal decreases, while upon its addition, it increases again. These results indicate that the strongly immobilized ESR signals belong to 2: 1: 2 complexes, which are formed upon the insertion of the second hydrocarbon molecule into the initial ternary 2: 1: 1 w-complexes. According to PM3 quantum-chemical calculations, 2: 1: 2 complexes are stable in energy and the geometry of hydrocarbon arrangement depends on the structure of the spin-labeled guest. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2094–2100, December, 2006.     

ESR spectroscopy of copper(ii) complexes with aza- and thia-containing crown ethers

Six copper(ii) chloride complexes with crown ethers containing besides oxygen also nitrogen or sulfur atoms in 15- or 18-membered cycle were studied by ESR and electron absorption spectroscopies. Theg and HFI tensor components determined by spectral simulation indicate rhombic symmetry and localization of an unpaired electron on the d _xy orbital for all the complexes. The unpaired electron fractions on - and -type metal ion and ligand AO were estimated from ESR and absorption spectra using LCAO MO method. Both - and -type bond covalences were shown to be greater in these complexes compared to only oxygen-containing crown ether complexes. The temperature dependence of g and A components in some complexes may be due to conformational changes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1938–1944, November, 1994.The present work was carried out with financial support from the Russian Foundation for Basic Research (Project 93-03 04089).     

Triplet-triplet energy transfer from aromatic to saturated compounds

Energy transfer from the upper triplet states of aromatic compounds to saturated compounds at 77 K has been investigated. Positions of triplet states of saturated molecules have been estimated in the ranges: 47800–48450 cm^?1 for methylcyclohexane, ethylcyclohexane, ethanol and ether, 47320–47800 cm^?1 for isopropylcyclohexane and transdecalin, and 48450–50000 cm^?1 for isoctane. The radius of the energy transfer sphere for biphenyl-d₁₀ and trans-decalin is found to be 5.1 Å. It is assumed that energy transfer occurs faster than vibrational relaxation.     

Photo-and thermoinitiated formation of J and H aggregates in amorphous dispersions of a carbocyanine dye

We revealed the possibility of formation of J and H aggregates with different structures in amorphous dispersions of 3,3′-di(γ-sulfopropyl)-4,4′,5,5′-dibenzo-9-ethylthiacarbocyanine betaine pyridinium salt prepared in ethanol-water binary solutions upon photoexcitation into the absorption band of the dye dispersion or temperature change.     

Crown ether styryl dyes

A novel styryl dye containing benzodithia-18-crown-6 andN-(4-sulfobutyl)benzothiazolium fragments was synthesized. The complex formation of thecis-isomers of several photochromic styryl dyes containing dithia-15(18)-crown-5(6) fragments with Hg²⁺ and Mg²⁺ ions was studied. The stability constants of the complexes with Mg²⁺ and the relative stability constants of the complexes with Hg²⁺ (with respect to benzo-1,10-dithia-18-crown-6 ether) were measured. The fact that the stability constant increases 11-fold on going from thetrans- to the correspondingcis-isomer was attributed to the formation of an anion-“capped” complex. For Part 22, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2213–2220, December, 1997.     

Spin exchange between transition metal complexes and nitroxyl radicals in nonaqueous media

New complexes of diaza- and tetraaza-containing crown ethers, viz., 1,10-diaza-18-crown-6 (1), 1,4,8,12-tetraazacyclopentadecane (2), 1,4,8,11-tetraazacyclotetradecane (3), and 1,4,8,11-tetraazacyclotetradecane 1,4,8,11-tetrachloride tetraacetic acid tetrahydrate (4), with the divalent copper and nickel ions and the Cl^–, Br^–, ClO₄ ^–, NO₃ ^–, and AcO^– counterions were synthesized. The exchange interactions of these compounds and paramagnetic copper and nickel salts with the TEMPO radical in MeOH—CHCl₃ binary mixtures of different compositions were studied. The plots of the linewidths of the hyperfine coupling components of TEMPO vs. concentration of the ions and temperature show that the frequency of diffusion collisions is the rate-limiting step for spin exchange (strong exchange regime). A strong dependence of the exchange rate constant (k _ex) on the crown ether and counterion structure was found. The isotropic hyperfine coupling constants (a _Cu) and g factors (g _i ) were measured for the Cu^II complexes with the crown ethers. In the case of the crown ether complexes 1—3 with CuCl₂, the a _Cu constant decreases linearly with an increase in g _i = g _i – 2.0023 in the series 3 < 2 < 1, whereas k _ex increases linearly in the same series with a decrease in the contact HFC on the Cu^II nucleus (K) and a decrease in covalence of bonding. For the complexes of 2 with Cu^II and different axial ligands (counterions), k _ex increases in the series Cl^– < ClO₄ ^– AcO^– Br^–; < NO₃ ^–. In the case of the complexes of 2 with NiCl₂, k _ex increases in the series 1 < 4 < 3 2. For the Cu^II and Ni^II salts with the Cl^–, ClO₄ ^–, and NO₃ ^– anions, the k _ex values are almost independent of the anion nature. The correlation of the k _ex values with the electron-spin parameters of the complexes is discussed.     

Dynamics of topological solitons in models with nonlocal interactions

A nondissipative generalization of the sine-Gordon equation to cases with nonlocal interactions is analyzed. A model of this sort is shown to describe signal propagation in a Josephson transmission line with a nonlocal inductive coupling. The incorporation of nonlocal interactions changes the properties of the model in a qualitative way, leading in particular to the appearance of some new soliton entities: 2kpi kinks, where k greater, similar 1. These entities do not arise in a local model. They are evolutionary, they interact with each other in a quasielastic fashion, and they can be generated in a corresponding transmission line.     

Self-compression of subgigawatt femtosecond laser pulses in a hollow photonic-crystal fiber

We report experimental evidence of waveguide self-compression for high-power Cr: forsterite-laser femtosecond pulses in a hollow photonic-crystal fiber. Dispersion spreading typical of low-intensity laser pulses is replaced by nonuniform compression for pulses with high power (above 100 MW) with the compression efficiency reaching its maximum around the peak of the laser pulse.     

Polarization nonlinear optics of quadratically nonlinear azopolymers

The polarization properties of second harmonic and sum-frequency signals generated by femtosecond laser pulses in films of polymers containing covalent groups of an azobenzothiazole chromophore polarized by an external electric field are investigated. It is shown that the methods of polarization nonlinear optics make it possible to determine the structure of oriented molecular dipoles and reveal important properties of the motion of collectivized π electrons in organic molecules with strong optical nonlinearities. The polarization measurements show that the tensor of quadratic nonlinear optical susceptibility of chromophore fragments oriented by an external field in macromolecules of the noted azopolymers has a degenerate form. This is indicative of a predominantly one-dimensional character of motion of collectivized π electrons along an extended group of atoms in such molecules.