Specifics of chemical etching of PbTe and Pb1 − x Sn x Te single crystals with I2-DMF solutions

The physicochemical interactions of Pb_{1 ? x} Sn _x Te solid solution and PbTe single crystals with I₂-DMF solutions were studied under reproducible hydrodynamic conditions for the first time. Their dissolution rates were investigated as dependent on the etchant components ratio and the temperature and stirring of etching blends, and the effect of the composition of solid solutions on the parameters of chemical etching was studied. Etchant compositions and the chemicodynamical polishing regimes for the studied single crystals were optimized.     

Photochemistry of trans-Cr(cyclam)(ONO)2+, a nitric oxide precursor

Experimental and density functional theory (DFT) studies are described that are focused on outlining the reactivity of the known photochemical nitric oxide precursor trans-Cr(cyclam)(ONO)(2)(+) ("CrONO", cyclam = 1,4,8,11-tetrazacycltetradecane). Studies in both aerated and deaerated aqueous media are described as are the roles of both the oxidant O(2) and a reductant such as glutathione in trapping the apparent Cr(IV) photoreaction intermediate trans-Cr(cyclam)(O)(ONO)(+). Also reported and characterized structurally is the Cr(V) product of long-term photolysis in the absence of reducing agents, the trans-dioxo species [trans-Cr(cyclam)(O)(2)](ClO(4)). Photosensitization experiments indicate that at least a significant fraction of the reaction occurs from the lowest energy doublet excited state(s). Lastly, cell culture experiments demonstrate that CrONO has little or no acute toxicity either before or after photolysis.     

Polyimide Dendrimers Containing Multiple Electron Donor–Acceptor Units and Their Unique Photophysical Properties

A high‐yielding synthesis of a series of polyimide dendrimers, including decacyclene‐ and perylene‐containing dendrimer D6 , in which two types of polyimide dyes are present, is reported. In these constructs, the branching unit is represented by trisphenylamine, and the solubilizing chains by N‐9‐heptadecanyl‐substituted perylene diimides. The photophysical properties of the dendrimers have been studied by absorption, steady‐state, and time‐resolved emission spectroscopy and pump–probe transient absorption spectroscopy. Photoinduced charge‐separated (CS) states are formed on the femtosecond timescale upon visible excitation. In particular, in D6 , two different CS states can be formed, involving different subunits that decays independently with different lifetimes (ca. 10–100 ps).     

Model for primary electron transfer and coupling of electronic states at reaction centers of purple bacteria

A detailed derivation is presented for relations making it possible to describe the effect of temperature on the halfwidth of the P960 and P870 absorption bands and also on the electron transfer (ET) rate at reaction centers (RCs) of the purple bacteria Rps. viridis and Rb. sphaeroides. Primary electron transfer is considered as a resonant nonradiative transition between P* and P⁺B _L ⁻ states (where P is a special pair, B_L is an additional bacteriochlorophyll in the L branch of the reaction center). It has been shown that the vibrational h_α mode with frequency 130–150 cm⁻¹ controls primary electron transfer. It has been found that the matrix element of the electronic transition between the states P* and P⁺B _L ⁻ is equal to 12.7 ± 0.9 and 12.0 ± 1.2 cm⁻¹ for Rps. viridis and Rb. sphaeroides respectively. The mechanism is discussed for electron transport from P* and B_L and then to bacteriopheophytin H_L. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 294–303, May–June, 2006.     

Solvatochromism and Nonradiative Decay of Intramolecular Charge‐Transfer Excited States: Bands‐of‐Energy Model,Thermodynamics, and Self‐Organization

The fluctuations of orientation and induction interactions in solution and their impact on the broadening of absorption and fluorescence spectra are considered in terms of a bands‐of‐energy model. Also covered is the application of principles of thermodynamics and self‐organization of systems for calculation of solvatochromic shift, among them a component owing to the work on electronic polarization of solvent at the instant of electronic transition in the solute. The findings on solvatochromic shift and spectral broadening open the way to the calculation of solvent effects on the rate constant of nonradiative transitions. As demonstrated herein for 15 fluorophores, the novel theory of nonradiative decay of the intramolecular charge‐transfer excited states is carried out for dyes and organic compounds of different nature, both for polar and nonpolar media.     

Relaxation of nonlinear oscillator

Institute of Nuclear Research, USSR Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 86, No. 3, pp. 367–374, March, 1991.