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.     

Photoinduced protonation and mechanical motion in the cyclodextrin cavity: Synthesis,structure and spectral properties of 4-(2-napthyl)pyridine and their pseudorotaxane complexes

The spontaneous and photoinduced protonation of 4-(2-naphthyl)pyridine (1) in solutions and in complexes with β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) were studied by absorption and fluorescence spectroscopy. The structure and stability of the complexes (log K = 1.5–2.3) of 1, its protonated form 2, and quaternized derivative, 1-methyl-4-(2-naphthyl)pyridinium perchlorate (3), with β-CD and HP-β-CD were studied by ¹H NMR. It was shown that irrespective of the solution pH, compound 1 resides in the cyclodextrin cavity. HP-β-CD better binds the neutral form of 1 than β-CD, while naphthylpyridinium salts have approximately equal binding affinity to both cyclodextrins. The structures of salt 3 and pseudorotaxane complex 1@β-CD were determined by X-ray diffraction analysis. According to spectral data, pK_a of 1 in water is 5.12, which promotes protonation of nitrogen both in the ground state and in the excited state. As a consequence, the fluorescence spectrum exhibits only the protonated form with a lifetime of 15 ns. The addition of HP-β-CD to a solution of 1 results in inclusion complex 1@HP-β-CD; simultaneously pK_a of 1 decreases to 4.62 and non-protonated form fluorescence (NFF) of 1 with a lifetime of 1.25 ns appears. Thus, the residence of 1 in the HP-β-CD cavity hampers its protonation in the excited state. From comparison of the initial regions of fluorescence of 1 in solution and in the HP-β-CD complex after pulse excitation, a mechanism for appearance of short-lived NFF of 1 was proposed. Quantum chemical simulation of the protonation and complexation of 1 in the presence of water was performed. On the basis of results, reversible photoinduced mechanical motion of 1 in the HP-β-CD cavity was suggested.     

Photoinduced processes in bis(diethylaminobenzylidene)cyclohexanone and its bis(aza-18-crown-6)-containing analogue in acetonitrile

Photoinduced processes in bis(diethylaminobenzylidene)cyclohexanone (CH1) and its bis(aza-18-crown-6) derivative (CH2) in acetonitrile at ambient temperature and 77 K have been studied. The absorption, fluorescence, and phosphorescence spectra of CH1 and CH2 are similar. The probability of the formation of the triplet state is higher for CH2 molecules (λ_T-T^max = 660 nm, lifetime τ_T ~ 20 μs). The lifetime of the CH1 molecule in the triplet state is estimated at τ_T ~ 2–3 μs. Photoisomers of CH1 and CH2 are formed along with the triplet state. According to DFT calculation results, the formation of trans–cis photoisomers of CH1 and CH2 is the most energetically favorable.     

Atomic structure of PtCu nanoparticles in PtCu/C catalysts from EXAFS spectroscopy data

Deposited electrocatalysts with different distributions of components in PtCu bimetallic nanoparticles involved in their composition were synthesized by simultaneous and sequential reduction of Cu(2+) and Pt(IV) in a carbon suspension. The dependence of the atomic structure of PtCu nanoparticles on the synthesis conditions and the degree of influence of post-treatment was established from analysis of the changes in Fourier transforms of the experimental Pt and Cu EXAFS spectra, as well as the structural parameters obtained by their fitting before and after the treatment of the materials in an acid solution. A technique was proposed for visualizing the atomic structure of synthesized bimetallic nanoparticles. This technique made it possible to determine the character of the distribution of the components over the nanoparticle volume in accordance with the component composition and local atomic structure parameters determined from EXAFS spectroscopy and to obtain the visualization of the distribution of the components in PtCu nanoparticles synthesized by the aforementioned methods.     

Coherent presentation of density operator of the harmonic oscillator in thermostat

Based on basis of the coherent states the density matrix of harmonic oscillator in thermostat is obtained. This method is mathematically refined and physically transparent for the interpretation of quantum phenomena in classical language. Such an approach gives an opportunity to easily find the density matrix in the multi-dimensional case.     

Thermal stability of the complex of pyrene–β-cyclodextrin dimer with aromatic amino acids

Russian Chemical Bulletin - Using the method of adsorption spectroscopy, the temperature dependence of the electronic absorption spectra of the fluorescent chemosensor (CS), based on the...