Specificity of photonics of 3,3′-diethyl-5,5′-dichloro-9-ethylthiacarbocyanine dimers in the presence of cucurbit[7]uril

Molecules of 3,3′-diethyl-5,5′-dichloro-9-ethylthiacarbocyanine form dimers in aqueous solutions, which are capable of fluorescence and intersystem crossing to the triplet state. In the presence of cucurbit[7]uril and alkali metals or ammonium cations, dye dimer complexes are formed, which exhibit phosphorescence and thermally activated delayed (E-type) fluorescence in air-saturated solutions at room temperature. With the use of quantum-chemical calculations, the structure of dimeric dye complexes with cucurbit[7]uril is suggested.     

Photochromic Transformations of Spiro Compounds: 1. A New Approach to Determining the Photocoloration Quantum Yield

A new approach to determining a photocoloration quantum yield for photochromic compounds was considered. This approach is based on comparison between the calculated and experimental values of maximum absorbance A ^B _maxof a photocolored form upon monochromatic irradiation. Using spirooxazines as an example, the quantum yield of photocoloration was determined, and A ^B _maxwas examined as a function of a number of parameters that characterize the photocolored form (the quantum yields of photocoloring and photobleaching and the lifetime of the colored form). It was found that A ^B _maxnonlinearly increased with decreasing rate constant (<0.2 s^–1) of the thermal bleaching of spirooxazines.     

Modeling the structure,absorption spectra,and cis-trans isomerization of thiacarbocyanine dyes

The relative stability of the trans-and cis-isomers of 3,3′-diethylthiacarbocyanine (Dye1) and 3,3′-diethyl-9-methylthiacarbocyanine (Dye2)¹, as well as sections of the potential energy surfaces along the internal coordinate of the isomerization reaction, were studied using the density functional theory. Calculation of the minimum energy pathway for the isomerization reaction showed that the barrier for rotation about the C₈–C₉ bond is higher for Dye1 than for Dye2. Local minimums were found for the singlet excited state of the 8,9-cis-and trans-isomers of the dyes. In the case of the trans-isomers, substantial changes in the dye structure do not occur and the local minimum of the excited state corresponds to the geometry of the starting trans-isomers, which favors efficient fluorescence. A search for the nearest local minimum of the singlet excited state of the 8,9-cis-isomers leads to structures, which differ significantly from the starting structures, and the intensity of the S₁ → S₀ transition in those structures appears to be practically zero. The results are in agreement with experimental data on the absorption, fluorescence, and fluorescence excitation spectra of the dyes.     

Effect of counterions on photoprocesses of thiacarbocyanine in a binary solvent blend

A model describing the effect of counterion X⁻ (X = Cl, I) on the deactivation kinetics of the S ₁ state of thiacarbocyanine Cy⁺X⁻ is presented. According to the model, the ion pair Cy⁺X⁻ in a binary solution is characterized by a distribution function f(r) over interatomic distances r, which depends on the composition of the mixture. The assumption of kinetically independent local states of the ion pair, which decay with the rate constants k _i(r)(i = 1–4 is the index of the decay channel), is made. The statistic analysis of the experimental data in terms of the model permitted us to find the functions f(r) and to estimate the parameters of the constants k _i(r).     

Ab initio simulation of the influence of zirconium impurity ions on the atomic and electronic structure of BaTiO<Subscript>3</Subscript>

The influence of zirconium impurity ions on the atomic and electronic structure of cubic barium titanate is studied theoretically by the electronic density functional theory and pseudopotential theory. It is shown that Zr ions induce local distortions in the BaTiO₃ lattice, although neither zirconium nor titanium ions shift from their ideal positions, so that the structure of BaTi_{1 − x} Zr _x O₃ compounds remains cubic. The introduction of zirconium in an amount of 37.5 at % broadens the energy gap by 0.18 eV.     

Characteristics of a hyperboloid-flare configuration at high Reynolds numbers

Results on a hyperboloid-flare model tested in a new hypersonic wind tunnel with adiabatic compression AT-303 based at ITAM SB RAS at M_∞ = 10 and 15 and in a wide range of Reynolds numbers are presented. Pressure and heat-flux distributions along the model are compared with data obtained previously in various European hypersonic wind tunnels (Longshot — Belgium, HEG — Germany) and with results of numerical computations. Pressure and heat-flux coefficients measured in the attached flow region are demonstrated to be in good qualitative agreement. Reasons for the differences in results measured in regions of flow separation and reattachment are discussed. Significant viscous effects on characteristics of the flow around the model are demonstrated; a particularly strong effect is exerted on the heat-flux distribution. This fact confirms that it is important to model real Reynolds numbers in wind-tunnel testing of aerospace plane models.     

Molecular photonics of inclusion complexes of cucurbit[7]uril with 3,3′-diethylthiazolinocarbocyanine iodide

The effect of cucurbit[7]uril (Cb7) on the photonics of 3,3′-diethylthiazolinocarbocyanine iodide (Car) in water was studied by spectrofluorimetry, ns-laser kinetic spectroscopy, and quantum chemistry. The formation of an inclusion complex of Car with Cb7 was established, and the binding constant and composition of the Car@Cb7 (1 : 2) complex were determined. It was shown that Car and Car@Cb7 are able to undergo trans → cis-photoisomerization. The lifetime of the cis-isomer of free Car was found to be much shorter than that of the cis-Car form localized inside the cavity of Cb7. The energies of formation of complexes Car@Cb7 were found and the structure of the complex in the lowest excited singlet state was determined according to the quantum chemical calculations by the DFT method with the PBE functional. The trans → cis-isomerization was found to proceed via the excited singlet S1 state having the “perpendicular” conformation.     

Effect of stoichiometry on the atomic and electronic structure of BaTiO3 nanoparticles: a first-principles study

We have used density functional theory calculations to investigate the atomic and electronic structure of barium titanate (BaTiO₃) nanoparticles. We studied the local atomic structure of different-sized stoichiometric and nonstoichiometric nanoparticle models in detail. Our results showed that all the stoichiometric BaTiO₃ clusters exhibit dielectric properties and form rhombohedral and monoclinic structures. However, oxygen deficient nonstoichiometric clusters show metallic behaviour and form cubic and tetragonal structures.     

Bis(15-crown-5)-1,4-distyrylbenzene and its complexes with metal perchlorates: photonics and structure

Russian Chemical Bulletin - Photoprocesses of bis(15-crown-5)-1,4-distyrylbenzene (DSB) and its complexes with barium and lead perchlorates in MeCN were studied by absorption, luminescence, and...