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Esophageal anastomoses leakage is a serious and urgent problem of surgical complications with high mortality rates. With the development of endoscopic technologies, minimally invasive methods of treatment are widely introduced into clinical practice with the development of endoscopic technologies in various non-standard situations, including esophageal anastomoses leakage. Stenting is one of the methods of choice in this case. However, the indicators of their effectiveness differ significantly across studies. A retrospective analysis of the stenting results in this severe complication demonstrates many factors influencing the success of esophageal stent implantation. Stents are often selected without due regard to their characteristics, which may affect the results of implantation. One of the most frequent and unfavorable outcomes of stenting is stent migration, which significantly affects the prognosis of the treatment. In this regard, in Russian practice, stenting, as a method of treating for esophageal anastomoses leakage, is introduced only in some institutions. However, many complications can be avoided at present due to the development in endoscopy and the constant improvement of stent designs. The objective of this review was to highlight the main advantages and problemsof stenting in esophageal anastomoses leakage today.

By precisely managing fiber-optic nonlinearity with anomalous dispersion, we have demonstrated the control of generating plural few-optical-cycle pulses based on a 24-MHz Chromium:forsterite laser, allowing multicolor two-photon tissue imaging by wavelength mixing. The formation of high-order soliton and its efficient coupling to dispersive wave generation leads to phase-matched spectral broadening, and we have obtained a broadband continuum ranging from 830 nm to 1200 nm, delivering 5-nJ pulses with a pulse width of 10.5 fs using a piece of large-mode-area fiber. We locate the spectral enhancement at around 920 nm for the two-photon excitation of green fluorophores, and we can easily compress the resulting pulse close to its limited duration without the need for active pulse shaping. To optimize the wavelength mixing for sum-frequency excitation, we have realized the management of the power ratio and group delay between the soliton and dispersive wave by varying the initial pulse energy without additional delay control. We have thus demonstrated simultaneous three-color two-photon tissue imaging with contrast management between different signals. Our source optimization leads to efficient two-photon excitation reaching a 500-µm imaging depth under a low 14-mW illumination power. We believe our source development leads to an efficient and compact approach for driving multicolor two-photon fluorescence microscopy and other ultrafast investigations, such as strong-field-driven applications.

Interactions of the electronic subsystem of the quadrupolar fluorophore with intramolecular highfrequency antisymmetric vibrations and solvent polarization are responsible for charge transfer symmetry breaking (SB), which is observed after optical excitation of such molecules in polar solvents. It is known that although these two interactions are mathematically described in similar ways, only the interaction of the fluorophore with solvent orientational polarization can create a state with broken symmetry if this interaction is strong enough. Nevertheless, the interaction of a quadrupolar fluorophore with intramolecular highfrequency antisymmetric vibrations in nonpolar solvents leads to a considerable reconstruction of the electronic subsystem. The analysis of the excited state of quadrupolar molecules in nonpolar solvents performed in this study reveals that such molecules can behave like quantum twostate systems, that is, as a quasispin s = 1/2, having an electric dipole moment instead of a magnetic one. This feature of excited quadrupolar molecules may be of interest to emerging technologies of molecular electronics.

The article considers the problem related to the correlation and regression analysis. The use of correlation and regression analysis methods is shown in the specific example illustrating the study of a particular economic situation. Special attention is paid to the use of the Excel Analysis Package, which significantly simplifies the solution of the problem from a computational standpoint.

В работе представлены полиорганосилоксановые адсорбенты, имеющие в своем составе один из органических радикалов с функциональными группами или без них, а также изучение их адсорбционных свойств по макрокомпонентам воздуха. В качестве базовой методики была выбрана схема «золь-гель» процесса, направленной сополиконденсации смеси реагентов. На основе отработанной методики синтеза были получены образцы полиорганосилоксанов с различными функциональными группами, имеющих в своем составе как четырехфункциональные фрагменты (Q-звенья), так и трехфункциональные (T-звенья). В свою очередь T-звенья имели один из органических радикалов с функциональными группами или без них. Равновесные емкости по азоту, кислороду и аргону были определены по кинетическим кривым адсорбции этих газов при 25оС и атмосферном давлении. В качестве меры адсорбционной селективности образцов по отношению к аргону использовали коэффициент разделения смеси аргон-кислород, который рассчитывали, как соотношение коэффициентов Генри. Для описания кинетики сорбции азота, кислорода и аргона были применены модель внутридиффузионной кинетики физической адсорбции, модели псевдопервого и псевдовторого порядка. В результате обработки кинетических данных показано, что механизм адсорбции макрокомпонентов воздуха на синтезированных полиорганосилоксанах имеет сложный характер, при этом влияние оказывают как свойства исследуемых газов, так и тип функциональной группы. Адсорбция аргона на полученных образцах лимитируется внутренней диффузией и с высоким уровнем достоверности описывается моделью квазигомогенного пористого тела. Адсорбция азота на полиорганосиланах определяется взаимодействием с локальными активными центрами поверхности, которыми являются силанольные группы кремнезема. Механизм адсорбции с высокой степенью достоверности описывается моделью химической кинетики псевдо-второго порядка. В скорость сорбции кислорода вносят вклад как внутридиффузионное лимитирование, так и скорость локализованной физической адсорбции, при этом влияние оказывает тип функциональной группы. Из представленных данных видно, что введением функциональных групп в полиорганосилоксаны можно влиять на адсорбционные свойства полученных материалов по макрокомпонентам воздуха. Наибольшую селективность к аргону проявил образец, содержащий диэтиламинометильную функциональную группу; значение коэффициента разделения составило 2.4.

Endoscopic esophageal stent implantation is an effective method for dysphagia management in malignant esophageal stricture. However, this technology is associated with the risk of many complications, including those fatal to life. These include bleeding, restenosis, stent fragmentation and destruction, stent migration, pneumomediastinum, the formation of esophageal fistulas, perforations, clogging of the stent with food, retrosternal pain, gastroesophageal reflux changes, airway compression, aspiration pneumonia, and fever. The overall complication rate is 3640%. Mortality rates associated with stenting is between 3.9 and 27.2%. Nevertheless, today there are ways to minimize the incidence of complications due to the constant progress of endoscopic technologies and improvements in the design of modern stents. In addition, most endoscopic interventions can manage the vast majority of complications effectively after stent implantation subject to their early detection. Optimal selection of an esophageal stent and careful selection of patients with a low risk of complications associated with stent implantation are important problems in the prevention of complications to achieve high efficiency of stenting. Evaluation of risk factors for possible complications, the design of stents and their characteristics, as well as using modern methods of effective management of possible complications improves the quality and duration of life in incurable patients with esophageal cancer. The review reflects all possible complications of stenting in esophageal and gastroesophageal junction, factors affecting the occurrence of complications, as well as modern and effective methods of their correction and prevention.

Aim. To analyze the results of one and two-step endoscopic submucosal dissection in the treatment of colorectal neoplasms. Methods. Between 2018 and 2019, 17 patients (6 men and 11 women) aged 33 to 79 years underwent 21 endoscopic submucosal dissections of colorectal neoplasms ranging in size from 1.0 to 6.0 cm. Submucosal fibrosis was identified in 2 (11.8%) patients, epithelial neoplasms in 15 (88.2%) patients including laterally spreading tumors in 9 (60%), and large sessile colorectal polyps in 6 (40%) patients. Histological examination revealed a carcinoid tumor (11.8%), adenoma with low-grade (64.7%) and high-grade (23.5%) intraepithelial neoplasia. 13 patients were subjected to the one-step operation, and 4 patients required the two-step operation with a 1-day interval. Follow-up examinations after the operation were performed, on average, between 2 and 6 months. Results. En bloc endoscopic submucosal dissection was performed in 11 (64.7%) patients, 4 of them in combination with mucosal resection. Endoscopic piecemeal resection of the neoplasia was performed in 6 (35.3%) patients. The average operative time was 15573 minutes (range 40320 min). Intraoperative complications, which were eliminated endoscopically, occurred during 8 (38.1%) of 21 operations: intensive bleeding in 6 (75%) patients, diastasis of muscle fibers in 1 (12.5%) patient, perforation of the intestinal wall in 1 (12.5%) patient. At the follow-up at 6 months, all patients formed the scar at the surgical area, while 3 patients required endoscopic removal of residual adenoma 2 months after the operation. Conclusion. Endoscopic submucosal dissection is an effective method for removing colorectal neoplasms, while two-step dissection is a promising approach to the development of the technique.Keywords: one and two-step dissection, endoscopic submucosal dissection (ESD), colorectal neoplasms.

A significant number of quadrupolar dyes with a D-$pi$-A-$pi$-D or A-$pi$-D-$pi$-A structure, where D and A are electron donor and acceptor groups, were shown to undergo symmetry breaking (SB) upon optical excitation. During this process, the electronic excitation, originally distributed evenly over the molecule, concentrates on one D-$pi$-A branch, and the molecule becomes dipolar. This process can be monitored by time resolved infra-red (TRIR) spectroscopy and causes significant spectral dynamics. A theoretical model of excited-state SB developed earlier ( extit{J. Phys. Chem. C}, extbf{2018}, extit{132}, 29165) is extended to account for the temporal changes taking place in the IR spectrum upon SB. This model can reproduce the IR spectral dynamics observed in the $-mathrm{C}equiv mathrm{C}-$ stretching region with a D-$pi$-A-$pi$-D dye in two polar solvents using a single set of molecular parameters. This approach allows estimating the degree of asymmetry of the excited state in different solvents as well as its change during SB. Additionally, the relative contribution of the different mechanisms responsible for the splitting of the symmetric and antisymmetric $-mathrm{C}equiv mathrm{C}-$ stretching bands, which are both IR active upon SB, can be determined.

An acridine-dione derivative (3,3,11,11-tetramethyl-8,16-diphenyl-3,4,8,10,11,12,13,16-octahydroacridino[4,3-c]acridine-1.9(2H,5H)dion) with quadrupolar motif has been synthesized and its stationary and transient spectra have been measured. Stationary absorption and fluorescence spectra as well as nonstationary spectra show no signs of symmetry breaking (SB) in aprotic solvents, even of high polarity. The specific features of SB are revealed in alcohol solvents through a considerable red shift of stationary fluorescence spectra and the appearance of a new excited state absorption band in transient absorption spectra. SB is due to the formation of asymmetric strong hydrogen bonds, mainly on one side of the molecule. An unexpected regularity of symmetry breaking is found in mixtures of aprotic dimethylformamide and protic methanol, where methanol acts as a fluorescence quencher. It is revealed that there is no quenching as long as the methanol concentration is less than the critical value of 9 M. This leads to the conclusion that SB in such mixtures is possible only if the concentration of the protic solvent exceeds a certain threshold value.

The paper analyses the parameters of deep oxidation of zinc and tin by copper (II) compounds and molecular iodine in the presence of molecular oxygen and hydrogen peroxide, as second oxidizers working synchronously with them in various media (aqueous, aqueous-organic and organic) with the participation of mineral and carboxylic acids close to room temperature. The contribution of the reactivity of the metal to its rate of consumption, especially the average, is often much less than the contribution associated with the release characteristics of the working surface, determined by the rates of accumulation of surface deposits of metal oxidation products, their strength and adhesion characteristics their destruction and shifting into the bulk phase.

Referring to the past era often intends to show the social and political system and, accordingly, focus is on the opinion of philosophers, sociologists, political scientists, etc. In this case, often on the sidelines is a person, his feelings, and attitude. This is evident in the attitude to the recent Soviet past of our country. In this regard, along with the coverage of the problem of time fixation in the artistic consciousness, we analyze the spiritual life of the transitional period, the main feature of which is the contradictory assessment of the 70-year history of the USSR. And it is not only about the nihilistic attitude, in the simplified denial of the Soviet experience, but also on ignoring the spiritual quest, the history of the formation of images and meanings inherent in our nation. The past time is not only economics and ideology, it is also artistic culture. Nihilistic atti-tude to the Soviet era is the way to oblivion of a huge cultural layer. It is an axiom which for some reason needs to be proved again and again. The social and cultural approach to the understanding of the past and present time has a greater tolerance in judgments and allows to fill the gaps in the public consciousness, to present spiritual life in diversity and uniqueness. The works of words, screen masters, sociologists conclusions contribute to the understanding of the recent past and the rapidly changing reality of the transition time.

A consistent theory of electron transfer symmetry breaking (SB) dynamics in excited quadrupolar molecules in polar solvents is developed. The interaction of the electronic subsystem of the molecule with intramolecular degrees of freedom and solvent polarization is taken into account and is divided into interaction with inertial and inertialess degrees of freedom. A strong influence of the inertialess polarization of the solvent on the extent of symmetry breaking is revealed. The theory is nonlinear due to the equilibration of inertialess degrees of freedom to the solute electronic state. The interaction of a molecule with the inertial solvent polarization is described in terms of a single variable-the reaction coordinate, for which a rigorous definition is given. The free energy of the system is derived, and the motion of the system along the reaction coordinate is modeled by the Smoluchowski equation. The theory is adapted to describe the dynamics of SB in real solvents characterized by several relaxation time scales. Conditions for the applicability of a much simpler stationary SB model are formulated. The role of thermal fluctuations in the solvent polarization is clarified. Instead of the magnitude of the dissymmetry parameter, a distribution function of molecules over this parameter is introduced. An analysis of the Franck-Condon state created by a short pump pulse shows that it has distinct features of a state with broken symmetry for a wide range of parameters. Thermal fluctuations of the solvent polarization are shown to crucially affect SB.

The efficiency of photoinduced charge separation (CS) in electron donor-acceptor compounds is commonly limited due to fast deactivation processes, such as the excited-state internal conversion and ultrafast hot reverse electron transfer to the acceptor, charge recombination (CR). A traditional way to avoid undesired energy losses due to CR is to put the reverse electron transfer into the Marcus inverted region, thus effectively suppressing it. This method, however, is not generally applicable when considering CS from the second locally excited state because the driving force of CR to the first excited state is small, and thus charge recombination is ultrafast and efficient. In this paper, we study the kinetic features of CS/CR from the second locally excited state of the donor using a semiclassical stochastic model of electron transfer. Particular attention is paid to the CS efficiency as well as the influence of the polar environment and intramolecular high-frequency vibrational modes on the kinetics of the charge-separated state. The influence of a number of model parameters on the CS yield and the energy efficiency has been analyzed using the results of numerical simulations. Several simple practical recipes for creating molecular compounds with high CS yields have been suggested. Simulations have also revealed a strong and non-monotonous (double-humped) dependence of both the yield and energy efficiency of CS on the driving force.

A general analytical expression for the transient fluorescence spectrum is derived. The formation of a wave packet in the excited state of a fluorophore is described, assuming that the pump pulse has a Gaussian time-profile. The expression explicitly connects the relaxation characteristics of the medium with the spectral dynamics of a fluorophore. Fitting the expression to experimental spectral dynamics allows obtaining the solvent relaxation function. So far this approach was applicable for the analysis of experimental data when the pump pulse does not populate excited sublevels of intramolecular high-frequency vibrational modes. Here, the approach is generalized to include vibrational relaxation in the excited electronic state. In this case, fitting to the experimental spectral dynamics provides reliable information not only on the solvent relaxation, but also on the relaxation time constants of intramolecular high-frequency vibrational modes. This approach is applied to the excited state dynamics of coumarin 153 in multiple solvents, obtained from broadband fluorescence upconversion spectroscopy.

To elucidate the regularities inherent in the kinetics of ultrafast charge recombination following photoinduced charge separation in donor-acceptor dyads in solutions, the simulations of the kinetics have been performed within the stochastic multichannel point-transition model. Increasing the solvent relaxation time scales has been shown to strongly vary the dependence of the charge recombination rate constant on the free energy gap. In slow relaxing solvents the non-equilibrium charge recombination occurring in parallel with solvent relaxation is very effective so that the charge recombination terminates at the non-equilibrium stage. This results in a crucial difference between the free energy gap laws for the ultrafast charge recombination and the thermal charge transfer. For the thermal reactions the well-known Marcus bell-shaped dependence of the rate constant on the free energy gap is realized while for the ultrafast charge recombination only a descending branch is predicted in the whole area of the free energy gap exceeding 0.2 eV. From the available experimental data on the population kinetics of the second and first excited states for a series of Zn-porphyrin-imide dyads in toluene and tetrahydrofuran solutions, an effective rate constant of the charge recombination into the first excited state has been calculated. The obtained rate constant being very high is nearly invariable in the area of the charge recombination free energy gap from 0.2 to 0.6 eV that supports the theoretical prediction.

Regularities of ultrafast charge recombination kinetics in photoinduced intramolecular electron transfer in polar solvent are investigated. The multichannel stochastic model is used to simulate kinetics of charge separation and ensuing ultrafast charge recombination. The rate constant of ultrafast charge recombination occurring in non-equilibrium mode is shown to depend on the free energy gap of the preceding charge separation stage. This is a clear demonstration of violation of one of the fundamental principles of formal chemical kinetics, namely, the postulate of independence of elementary chemical reactions. The simulations revealed two main trends: (i) the charge recombination rate constant typically increases with decreasing the charge separation free energy gap, (ii) the maximum of the charge recombination rate constant, as a function of the charge recombination free energy gap, |ΔGCR|, shifts toward smaller values of |ΔGCR| with decreasing the free energy gap at the previous, charge separation, stage of the reaction. The prediction of ultrafast charge recombination in donor–acceptor dyads with small charge recombination free energy gap is shown to be supported by the experimental data on the kinetics of charge recombination into the first excited state followed the charge separation from the second excited state.

The aim of our research was to determine the possibilities to stratify patients with papillary thyroid cancer (PTC) on the group’s forecast, depending on the status of the mutation BRAF v600e and Ki-67 expression. The study included 89 PTC patients with the known prognosis for the period of 2005-2015. They were treated in the Altai regional oncology center and underwent surgery for PTC over the period of 2005-2013. Mutation p. Val600Glu (V600E) BRAF gene was determined with the use of allele-specific real-time PCR kit «Real-time-PCR-BRAF-V600E («BioLink»)». Immunohistochemical examination was performed with antibodies Ki-67 (clone MIB1, «DAKO») on stainer «Ventana XT» according to standard protocols. We revealed BRAF V600E not to be an independent predictor. Different variants of PTC, depending on the level of expression of Ki-67 in combination with a mutation of BRAF V600E was allowed to identify 3 groups of molecular types of PTC: a lack of mutation and a low Ki-67 (type I), with mutation and a low Ki-67 (type II) and with the presence and/or absence of a mutation and high level Ki-67 (type III). I molecular type PTC is the most favorable from the point of view of survival: 100% of patients live 10 years. Molecular type II is characterized by an intermediate prognosis: 76% of patients lived out up to 10 years. Molecular type III is characterized by the poor prognosis: only 36.8 percent of cases lived up to 10 years. In multivariate analysis of survival in PTC patients the independent prognostic factor happened to be the molecular type of tumor. In this case χ2 = 35 at p ≤ 0.000005.

Control of charge transfer requires knowledge of its detailed mechanism. Due to the large number of known mechanisms, the identification of the mechanism in specific systems is a challenge so far. In this article we propose the idea of how to distinguish between thermal and nonequilibrium modes of charge recombination in excited donor-acceptor complexes. Simulations of the effect of solvent relaxation time scale on ultrafast charge recombination kinetics in photoexcited donor-acceptor complexes within the framework of the multichannel stochastic model have shown that a series of regularities inherent to the thermal and nonequilibrium charge transfer can strongly differ. Among them there are opposite regularities, for example, the dependence of the dynamic solvent effect on the free energy gap. In particular, theory predicts that in ultrafast charge recombination of excited donor-acceptor complexes the dynamic solvent effect is weak in the area of weak exergonicity and becomes stronger in the area of stronger exergonicity whereas for the thermal reactions an opposite trend is expected. Comparison of such trends with experimental data implemented in this article allowed establishing the regime in which the reaction proceeds. It is shown that observation of dynamic solvent effect in the region of strong exergonicity for ultrafast charge recombination is decisive evidence in favor of nonequilibrium mechanism.

In this article, regularities of ultrafast charge recombination (CR) kinetics in photoinduced intramolecular electron transfer in polar solvents are studied. The kinetics of charge separation and ensuing ultrafast CR are simulated within the framework of the multichannel stochastic model. This model accounts for the reorganization of both the solvent and a number of intramolecular high-frequency vibrational modes. The solvent relaxation is described in terms of two relaxation modes. For ultrafast CR, the free-energy-gap law strongly depends on the parameters: the electronic coupling, reorganization energy of intramolecular high-frequency vibrational modes, and the vibrational and solvent relaxation times. The semilog dependence of the CR rate constant on the free-energy gap varies from a parabolic shape to a nearly linear one with increasing the electronic coupling and decreasing the vibrational relaxation time. The dynamic solvent effect in CR is predicted to be large in the area of strong exergonicity and small in the area of weak exergonicity. This regularity is opposite to that observed for the thermal reactions.

Modern laser-based spectroscopy has provided methods for detection ultrafast photochemical transformations occurring on the timescale of intramolecular and solvent reorganization. Such processes usually proceed in non-equilibrium regime, in parallel with nuclear relaxation, and often manifest strong deviations from the Kasha–Vavilov rule. In particular, they offer a possibility to control the yield of photoinduced electron transfer (ET) by using different excitation wavelengths. In the last decade the non-equilibrium charge transfer (CT) processes have attracted considerable interest from the scientific community due to their determining role in photosynthesis, dye-sensitized solar cells and various molecular electronic devices. Non-equilibrium of nuclear (intramolecular and solvent) degrees of freedom can be created by a pump pulse or by photoreaction itself at some of its stages. In this review both situations are considered and illustrated by examples in which non-equilibrium effects are pronounced. It is shown that ultrafast charge recombination in photoexcited donor–acceptor complexes and photochemical processes in donor–acceptor1–acceptor2 molecular compounds proceed predominantly in non-equilibrium (hot) regime. It is important that kinetics and product yields of these reactions demonstrate regularities that considerably differ from that observed in thermal reactions. Among them, the lack of the Marcus normal region in the free energy gap law for charge recombination of the excited donor–acceptor complexes, extremely low quantum yields of the thermalized charge separated states in ultrafast CT from the second excited state of the donor are most known. Although there have been many efforts to clarify microscopic mechanisms of non-equilibrium photoreactions by using ultrafast time-resolved spectroscopy techniques, control of the rate and efficiency of photoinduced charge transfer reactions is still an open challenge. One of the most important applications here is a suppression of ultrafast charge recombination in CT systems, formed either by direct optical excitation or by the preceding ET step. In these systems charge recombination is often regarded as undesirable process, leading to the loss of energy and selectivity of photoreaction. In this review some strategies of ultrafast charge recombination suppression are discussed. The non-equilibrium effects are interpreted from a unified point of view in context of the multichannel point-transition stochastic model. This approach demonstrates similarities and differences in ET mechanisms in various donor–acceptor molecular systems and allows formulating general regularities inherent to these phenomena. We believe that new advances in this research area will not only help to discover new fundamental information about these regularities, but will also have impact on many emerging technologies where ultrafast CT plays the central role.

Nitro derivatives of xanthione, 2,7-dinitro-9 H-xanthene-9-thione and 2,4,7-trinitro-9 H-xanthene-9-thione, have been first synthesized and their stationary and transient spectra have been measured. The stationary spectra show that the attachment of the nitro groups to the xanthione scaffold leads to strong quenching of S

The dynamics of the ion pairs produced upon fluorescence quenching of the electron donor 9,10-dimethylanthracene (DMeA) by phthalonitrile have been investigated in acetonitrile and tetrahydrofuran using transient absorption spectroscopy. Charge recombination to both the neutral ground state and the triplet excited state of DMeA is observed in both solvents. The relative efficiency of the triplet recombination pathway decreases substantially in the presence of an external magnetic field. These results were analyzed theoretically within the differential encounter theory, with the spin conversion of the geminate ion pairs described as a coherent process driven by the hyperfine interaction. The early temporal evolution of ion pair and triplet state populations with and without magnetic field could be well reproduced in acetonitrile, but not in tetrahydrofuran where fluores- cence quenching involves the formation of an exciplex. A description of the spin conversion in terms of rates, i.e., incoherent spin transitions, leads to an overestimation of the magnetic field effect.

We study the fluorescence spectral dynamics of a molecule with two excited fluorescent states (called the precursor and product) within the stochastic point transition model, which includes a consistent description of the dynamics of the particles distribution in excited states and transitions between them. Crucial changes in spectral dynamics with increasing the transition rate between the precursor and the product are discovered. Analysis of the results of spectral dynamics modeling allows us to determine how the transition rate between the precursor and the product affects the isoemissive point in the spectra collected with an increasing time delay. The following main regularities were revealed: fluorescence spectra with a short delay not exceeding several solvent relaxation times ( τ L ) may not pass through the isoemissive point; the isoemissive point shifts to the red with a decrease in reaction time constant ( τ eff ). The shifted isoemissive point exists in the range 10 τ L τ eff 40 τ L . For faster reactions with 5 τ L τ eff 10 τ L , the isoemissive point blurs. When the reaction proceeds in the ultrafast regime τ eff 5 τ L , the fluorescence spectrum shifts from a vicinity of the precursor spectrum to the product spectrum as a whole, changing its shape.

Aim. To approbate method of endoscopic removal of esophagus and stomach polyps using a ligation device.Methods. During the period from 2013 to 2015, 37 endoscopic polyps removal using the variceal band ligation device «G-Flex» (Belgium) were performed to 34 patients (26 women and 8 men) aged 17 to 68 years. Removed polyps size ranged from 5 to 11 mm. Polyps localization was as follows: esophagus abdominal part and stomach cardia - 7 (19%), stomach subcardial part - 2 (5%), stomach body - 19 (52%), antrum - 9 (24%). Before polyps removal, lesions biopsy and gastric juice acidity determination were performed to all patients, in 45% of cases endosonography was performed. According to the histological study results, hyperplastic polyps were detected in 5 (15%) patients, adenomatous polyps - in 29 (85%). In 2 patients the endosonography results revealed submucosal lesion, coming from the mucous membrane muscular layer.Results. Technical possibilities of the esophagus and stomach polyps endoscopic removal using variceal band ligation device, depending on the lesion location and size, were evaluated. In all cases, regardless of the focus localization and the comorbidity severity, a successful technical surgery performance was achieved in the absence of complications and symptoms recurrence in the early and late postoperative periods. Method advantages and disadvantages, indications for its performance in the inpatient and outpatient settings are revealed.Conclusion. In certain indications and performance technique adherence, the esophagus and stomach polyps endoscopic removal using variceal band ligation device is a safe and radical method of upper gastrointestinal tract benign epithelial lesions treatment.

Ultrafast photoinduced intramolecular charge separation from the second excited singlet state of Zn–porphyrin–amino naphthalene diimide dyad in toluene solution is theoretically studied in the framework of a multichannel stochastic model. The model incorporates four electronic states (the first and the second singlet excited, the charge separated, and the ground states) as well as their vibrational sublevels corresponding to the excitation of intramolecular high frequency vibrational modes. Electron transfer from the second excited state results in creation of the charge separated state with strongly non-equilibrium surrounding solvent and the intramolecular vibrations. The solvent motion to its equilibrium is described in the terms of three relaxation modes. The model explicitly describes the hot transitions from the charge separated state into the first excited state occurring in the course of the nuclear relaxation. Upon termination of the ultrafast decay of the second excited state as well as the relaxation of the solvent and intramolecular vibrations, the populations of the first excited, the ground, and the charge separated states can be far from the thermal equilibrium. Further, the populations approach their equilibrium values in the thermal regime. Simulations of the kinetics of the charge separated state population allow quantitative reproducing the two-humped kinetic curve observed in the experiment. The results of the fitting indicate that the reorganization energy of intramolecular low frequency modes for the intramolecular charge separation from the second excited state is extremely large in the porphyrin–diimide dyad.

A simple model has been developed to describe the symmetry-breaking of the electronic distribution of AL–D–AR type molecules in the excited state, where D is an electron donor and AL and AR are identical acceptors. The origin of this process is usually associated with the interaction between the molecule and the solvent polarization that stabilizes an asymmetric and dipolar state, with a larger charge transfer on one side than on the other. An additional symmetry-breaking mechanism involving the direct Coulomb interaction of the charges on the acceptors is proposed. At the same time, the electronic coupling between the two degenerate states, which correspond to the transferred charge being localised either on AL or AR, favours a quadrupolar excited state with equal amount of charge-transfer on both sides. Because of these counteracting effects, symmetry breaking is only feasible when the electronic coupling remains below a threshold value, which depends on the solvation energy and the Coulomb repulsion energy between the charges located on AL and AR. This model allows reproducing the solvent polarity dependence of the symmetry-breaking reported recently using time-resolved infrared spectroscopy.

A model for simulating the transient electronic absorption spectra of donor-acceptor dyads undergoing ultrafast intramolecular charge transfer in solution has been developed. It is based on the stochastic multichannel point-transition approach and includes the reorganization of high-frequency intramolecular modes (treated quantum mechanically) and of low frequency intramolecular and solvent modes (described classically). The relaxation of the slow modes is assumed to be exponential with time constants taken from experiments. The excited-state dynamics is obtained by simulating the population distribution of each quantum state after optical excitation and upon electronic and vibrational transitions. This model was used to simulate the transient electronic absorption spectra measured previously with a pyrylium phenolate in acetonitrile. A very good agreement between the simulated and measured spectra was obtained assuming a three-level model including the ground state, the optically excited state, and a dark state with large charge-transfer character and a substantially different geometry relative to that of the optically excited state. The merit of this approach to disentangle the contributions of both population changes and relaxation processes to the ultrafast spectral dynamics will be discussed.

Ultrafast intramolecular charge transfer induced by the Soret-band excitation of the donor-acceptor1-acceptor2 molecular triads has been explored within the stochastic point-transition model. It is shown that nonthermal (hot) charge transfer from the primary to the secondary acceptor, assisted by relaxation of solvent polarization, can effectively screen ultrafast back electron transfer into the first excited state of the donor. Ways to increase the quantum yield of the charge-separated states are discussed. The dependencies of the quantum yield of the charge-separated states on the main electron transfer parameters: the free energy gaps, the reorganization energy of the solvent and intramolecular vibrational modes, the electronic couplings, and the solvent relaxation timescale are revealed. The important role of the geometry of the donor-acceptor1-acceptor2 triad in charge separation effectiveness is emphasized. For the zinc-porphyrin-imide1-imide2 triad, the charge-transfer parameters maximizing the quantum yield of the charge separated states are estimated.

Manifestation of the dynamic solvent effect (DSE) on the charge recombination (CR) kinetics of photoexcited donor-acceptor complexes in polar solvents has been investigated within the framework of the multichannel stochastic model. The model takes into account the reorganization of both the solvent and a number of intramolecular high-frequency vibration modes as well as their relaxation. The non-Markovian solvent dynamics is described in terms of two relaxation modes. The similarities and differences inherent to ultrafast charge transfer reactions occurring in the nonequilibrium and thermal regimes have been identified. The most important differences are as follows: (1) the DSE is strong in the area of weak exergonicity and is weak in the area of strong exergonicity for thermal reactions, whereas for the nonequilibrium reactions, the regions of strong and weak DSEs are reversed; (2) an increase in the electronic coupling value results in a decrease in the magnitude of DSE for nonequilibrium electron transfer and in its increase for the thermal reactions; and (3) the two-staged regime most clearly manifests if the reorganization energy of the relaxation modes noticeably exceeds the CR free-energy gap. With an increase in electronic coupling, the kinetics approaches the exponential regime because in the limit of strong electronic coupling, the reaction includes only single, nonequilibrium, stage.

A model of photoinduced ultrafast charge separation and ensuing charge recombination into the ground state has been developed. The model includes explicit description of the formation and evolution of nonequilibrium state of both the intramolecular vibrations and the surrounding medium. An effect of the high-frequency intramolecular vibrational mode excitation by a pumping pulse on ultrafast charge separation and charge recombination kinetics has been investigated. Simulations, in accord with experiment, have shown that the effect may be both positive (the vibrational mode excitation increases the charge-transfer rate constant) and negative (opposite trend). The effect on charge separation kinetics is predicted to be bigger than that on the charge recombination rate but nevertheless the last is large enough to be observable. The amplitude of both effects falls with decreasing vibrational relaxation time constant, but the effects are expected to be observable up to the time constants as short as 200 fs. Physical interpretation of the effects has been presented. Comparisons with the experimental data have shown that the simulations, in whole, provide results close to that obtained in the experiment. The reasons of the deviations have been discussed.

The possibility of the multichannel stochastic model to adequately describe all principal regularities observed in thermal electron transfer kinetics has been demonstrated. The most important are as follows: (i) the model predicts the solvent controlled regime in the Marcus normal region and its almost full suppression in the Marcus inverted region as well as a continuous transition between them in the vicinity of the activationless region; (ii) the suppression of dynamic solvent effect (DSE) is principally caused by the reorganization of high frequency vibrational modes; (iii) an additional factor of the DSE suppression stems from fast solvent relaxation component; (iv) in the inverted region, the multichannel stochastic model predicts the apparent activation energy to be much less than that calculated with Marcus equation. The exploration of the multichannel stochastic model has allowed one to conclude that the reorganization of high frequency vibrational modes can (i) raise the maximum rate constant above the solvent controlled limit by 2 and more orders of magnitude, (ii) shift the rate constant maximum to larger values of the free energy gap, and (iii) approach the electron transfer kinetics to the nonadiabatic regime.

Intramolecular charge separation from the second singlet excited state of directly linked Zn-porphyrin-imide dyads and following charge recombination into the first singlet excited state has been investigated in the framework of a model involving three electronic states (the first and the second singlet excited and charge separated states) as well as their vibrational sublevels. Kinetics of the transitions between these states are described in terms of the stochastic point-transition approach. The influence of the model parameters (free energy change of charge separation, magnitude of the reorganization energies of the medium and the high frequency intramolecular vibrations, the rate of relaxation of the medium and the intramolecular high frequency vibrational mode) on the kinetics of population of both the charge separated and the first singlet excited states has been explored. Simulations of the kinetics of the charge separated state population have allowed reproducing the distinctive features of the kinetics observed in the experiment [Wallin, S.; Monnereau, C.; Blart, E.; Gankou, J.-R.; Odobel, F.; Hammarström, L. J. Phys. Chem. A 2010, 114, 1709]: (i) two maxima on short time scale (hundreds of femtoseconds) and long time scale (tens of picoseconds), (ii) the magnitudes of both maxima, and (iii) the depth of the notch between the maxima.

The charge recombination dynamics of excited donor-acceptor complexes in polar solvents has been investigated within the framework of the stochastic approach. The model involves the excited state formation by the pump pulse and accounts for the reorganization of a number of intramolecular high-frequency vibrational modes, for their relaxation as well as for the solvent reorganization following nonexponential relaxation. The hot transitions accelerate the charge recombination in the low exergonic region and suppress it in the region of moderate exothermicity. This straightens the dependence of the logarithm of the charge recombination rate constant on the free energy gap to the form that can be fitted to the experimental data. The free energy dependence of the charge recombination rate constant can be well fitted to the multichannel stochastic model if the donor-acceptor complexes are separated into a few groups with different values of the electronic coupling. The model provides correct description of the nonexponential charge recombination dynamics in excited donor-acceptor complexes, in particular, nearly exponential recombination in perylene-tetracyanoethylene complex in acetonitrile. It appears that majority of the initially excited donor-acceptor complexes recombines in a nonthermal (hot) stage when the nonequilibrium wave packet passes through a number of term crossings corresponding to transitions toward vibrational excited states of the electronic ground state in the area of the low and moderate exothermicity.

A model of the intramolecular charge separation from the second singlet excited-state of directly linked Zn-porphyrin-imide dyads and following charge recombination into the first singlet excited-state has been constructed and investigated. The model incorporates three electronic states (the first and the second singlet excited and charge separated states) as well as their vibrational sublevels. Dynamics of the transitions between these states are described in the framework of the stochastic point-transition approach. The relaxation of the intramolecular high frequency vibrational mode is supposed to occur as a single-quantum transition between nearest states with a time constant depending on the number of the vibrational state. The medium relaxation is characterized by two timescales. A good fitting to experimentally observed population dynamics of both the first and the second singlet excited states has been obtained. The calculations show the charge recombination into the first excited-state to proceed in a hot stage in parallel with the relaxation of both the medium and the intramolecular high-frequency vibrational mode.

The Hamiltonian description of the spin-conversion induced by a hyperfine interaction (HFI) in photogenerated radical-ion pairs is substituted for the rate (incoherent) description of the same conversion provided by the widely used earlier elementary spin model. The quantum yields of the free ions as well as the singlet and triplet products of geminate recombination are calculated using distant dependent ionization and recombination rates, instead of their contact analogs. Invoking the simplest models of these rates, we demonstrate with the example of a spin-less system that the diffusional acceleration of radical-ion pair recombination at lower viscosity gives way to its diffusional deceleration (Angulo effect), accomplished with a kinetic plateau inherent with the primitive exponential model. Qualitatively the same behavior is found in real systems, assuming both ionization and recombination is carried out by the Marcus electron-transfer rates. Neglecting the Coulomb interaction between solvated ions, the efficiencies of radical-ion pair recombination to the singlet and triplet products are well fitted to the available experimental data. The magnetic field dependence of these yields is specified.

A theoretical approach to simulation of the transient spectra in molecular systems with ultrafast photoinduced nonradiative electronic transitions is developed. The evolution of the excited and ground state populations as well as the nonradiative transitions between them are calculated in the framework of the stochastic multichannel point-transition model involving the reorganization of the medium and the intramolecular high frequency vibrational modes. Simulations of transient spectra of donor-acceptor pairs excited in the charge-transfer band that are accompanied by ultrafast charge recombination into the ground state demonstrate a possibility of positive band appearance in the transient absorption spectrum caused by those systems in the ground state, which returned there from the excited state. The region of the parameters of the donor-acceptor systems where a positive ground state absorption signal can be observed is discussed. A qualitative comparison of the simulated transient spectra with the experimental data on betaine-30 is presented.

A model of nonequilibrium charge recombination from an excited adiabatic state of a donor-acceptor complex induced by the nonadiabatic interaction operator is considered. The decay of the excited state population prepared by a short laser pulse is shown to be highly nonexponential. The influence of the excitation pulse carrier frequency on the ultrafast charge recombination dynamics of excited donor-acceptor complexes is explored. The charge recombination rate constant is found to decrease with increasing excitation frequency. The variation of the excitation pulse carrier frequency within the charge transfer absorption band of the complex can alter the effective charge recombination rate by up to a factor 2. The magnitude of this spectral effect decreases strongly with increasing electronic coupling.

The excitation of a charge transfer band by a laser pulse of finite duration and the ensuing charge recombination are calculated in the framework of the perturbation theory. The influence of the spectral characteristics of the laser pulse on the charge recombination dynamics is investigated for models including several nuclear modes that differ greatly in their timescales. It is shown that, in the area of applicability of the perturbation theory, the variation of the pulse carrier frequency inside the absorption band can significantly change the effective charge recombination rate constant.

The multichannel stochastic point transition model of photoinduced electron transfer from both a vibrationally unrelaxed and a relaxed states involving the vibrational relaxation in donor-acceptor pairs has been elaborated. The U-shaped temperature dependencies of the rate constants of the intramolecular photoinduced charge separation from both the vibrationally unrelaxed and the relaxed states observed in Zn-porphyrin-bridge-quinone compounds in 2-methyltetrahydrofuran solvent have been reproduced in the framework of the proposed model that accounts for the temperature dependencies of the charge separation free energy gap and the medium reorganization energy. This modeling has allowed uncovering the mechanism of such a variation of the rate constant with the temperature. In the high temperature region, 310-125 K, the charge separation proceeds in the solvent controlled regime and its rate constant decreases with decreasing the temperature mirroring the temperature dependence of the medium relaxation rate. Further lowering the temperature leads to a rise of the reaction free energy gap so that it becomes larger than the medium reorganization energy. In this region the dynamic solvent effect is strongly suppressed and the charge separation rate constant becomes independent from the solvent relaxation rate. Although the medium relaxation rate continues to decrease with decreasing the temperature, the charge separation rate constant starts to rise because the reaction proceeds in the barrierless region.

Intramolecular charge separation from the second singlet excited state of directly linked Zn-porphyrin-imide dyads and following charge recombination into the first singlet excited and the ground states has been investigated in the framework of a model incorporating four electronic states (the first and the second singlet excited, the charge separated, and the ground states) as well as their vibrational sublevels. Kinetics of the transitions between these states are described in terms of the stochastic point-transition approach involving reorganization of a number of high frequency vibrational modes. The influence of the model parameters (the number of high frequency vibrational modes, the magnitude of the reorganization energies of the medium and the high frequency intramolecular vibrations, the solvent polarity) on the kinetics of population of the second and first singlet excited states as well as the charge separated state has been investigated. Simulation of the kinetics of the charge separated state population allows quantitative reproducing of the distinctive features of the two-humped kinetic curve observed in the experiment.

Kinetics of photoinduced electron transfer reactions in [Ru(II)(L-L)Co(III)](5+) complexes have been investigated in the framework of the stochastic point-transition model. The model involves the medium and intramolecular nuclear reorganization as well as fast relaxation of intramolecular high frequency vibrations and description of the medium relaxation in terms of two time scales. The model has allowed reproducing the experimental data (Torieda, H.; Nozaki, K.; Yoshimura, A.; Ohno, T. J. Phys. Chem. A2004, 108, 4819) of forward and backward electron transfer kinetics, including the low yield of electron transfer products and its variation with solvent. These results have lent support to the important role of hot backward electron transfer in the formation of low yield of electron transfer products. The experimentally observed significant decrease of the product yield in more viscous solvents has been shown to be a direct consequence of the hot transition efficiency increase. A weak opposite dependence, also revealed in experiments, has been elucidated in terms of two time scales of the solvent relaxation. Solvent relaxation is well-known to involve at least two stages: the inertial one (fast) and the diffusive one (slower) with the time scales weakly dependent on and proportional to solvent viscosity, respectively. When hot transitions are terminated at the stage of the inertial relaxation, the yield of the electron transfer products is nearly independent of the diffusive time scale; otherwise a strong increase of the yield in more viscous solvents should be observed.

Photonic-crystal fibers (PCFs) provide a high efficiency of frequency upconversion of femtosecond Cr: forsterite laser pulses through the emission of dispersive waves by solitons and third-harmonic generation. Dispersion management allows the central wavelength of the frequency-upconverted signal in PCF output to be tuned within the range of wavelengths from 400 to 900 nm. PCF frequency shifters are employed as excitation sources for time-resolved fluorescence streak-camera measurements on fluorescein solution.

The dynamics of charge recombination in a photoexcited donor-acceptor complex comprising 1,2,4-trimethoxybenzene (electron donor) and tetracyanoethylene (electron acceptor) in several polar solvents (acetonitrile, valeronitrile, and octanonitrile) was studied in terms of the stochastic approach. The Gibbs energy of charge recombination and the reorganization energies of the medium and quantum and vibrational degrees of freedom were found by fitting the stationary absorption spectrum. The electronic couplings were determined by analyzing the time dependences of the population of the ionic state in acetonitrile. A comparison of the numerical simulation results with the experimental data showed that the nonstationary model under consideration quantitatively described the dynamics of charge recombination and its dependence on the carrier frequency of excitation pulses and the relaxation properties of solvents.

The kinetics of fluorescence quenching by both charge transfer and exciplex formation is investigated, with an emphasis on the reversibility and nonstationarity of the reactions. The Weller elementary kinetic scheme of bimolecular geminate ionization and the Markovian rate theory are shown to lead to identical results, provided the rates of the forward and backward reactions account for the numerous recontacts during the reaction encounter. For excitation quenching by the reversible exciplex formation, the Stern-Volmer constant is specified in the framework of the integral encounter theory. The bulk recombination affecting the Stern-Volmer quenching constant makes it different for pulse excited and stationary luminescence. The theory approves that the free energy gap laws for ionization and exciplex formation are different and only the latter fits properly the available data (for lumiflavin quenching by aliphatic amines and aromatic donors) in the endergonic region.