A new method for calculating internal conversion rate constants (
k&cmb.b.line;
IC
), including anharmonic effects and using the Lagrangian multiplier technique, is proposed. The deuteration effect ...on
k&cmb.b.line;
IC
is investigated for naphthalene, anthracene, free-base porphyrin (
H
2
P
) and tetraphenylporphyrin (
H
2
TPP
). The results show that anharmonic effects are important when calculating
k&cmb.b.line;
IC
for transitions between electronic states that are energetically separated (Δ
E
) by more than 20 000-25 000 cm
−1
. Anharmonic effects are also important when Δ
E
< 20 000-25 000 cm
−1
and when the accepting modes are X-H stretching vibrations with a frequency larger than 2000 cm
−1
. The calculations show that there is mixing between the S
1
and S
2
states of naphthalene induced by non-adiabatic interactions. The non-adiabatic interaction matrix element between the S
1
and S
2
states is 250 cm
−1
and 50 cm
−1
for the normal and fully deuterated naphthalene structure and this difference significantly affects the estimated fluorescence quantum yield. Besides aromatic hydrocarbons
H
2
P
and
H
2
TPP
, the
k&cmb.b.line;
IC
rate constant is also calculated for pyrometene (PM567) and tetraoxa8circulene (4B) with a detailed analysis of the effect of the vibrational anharmonicity.
A new method for calculating internal conversion rate constants (
k
IC
), including anharmonic effects and using the Lagrangian multiplier technique, is proposed.
A method for calculating the rate constants for internal-conversion (k
) and intersystem-crossing (k
) processes within the adiabatic and Franck-Condon (FC) approximations is proposed. The ...applicability of the method is demonstrated by calculation of k
and k
for a set of organic and organometallic compounds with experimentally known spectroscopic properties. The studied molecules were pyrromethene-567 dye, psoralene, hetero8circulenes, free-base porphyrin, naphthalene, and larger polyacenes. We also studied fac-Alq
and fac-Ir(ppy)
, which are important molecules in organic light emitting diodes (OLEDs). The excitation energies were calculated at the multi-configuration quasi-degenerate second-order perturbation theory (XMC-QDPT2) level, which is found to yield excitation energies in good agreement with experimental data. Spin-orbit coupling matrix elements, non-adiabatic coupling matrix elements, Huang-Rhys factors, and vibrational energies were calculated at the time-dependent density functional theory (TDDFT) and complete active space self-consistent field (CASSCF) levels. The computed fluorescence quantum yields for the pyrromethene-567 dye, psoralene, hetero8circulenes, fac-Alq
and fac-Ir(ppy)
agree well with experimental data, whereas for the free-base porphyrin, naphthalene, and the polyacenes, the obtained quantum yields significantly differ from the experimental values, because the FC and adiabatic approximations are not accurate for these molecules.
Magnetically induced current densities have been calculated at the second-order Møller-Plesset perturbation theory (MP2) level for seven hetero8circulenes and their dicationic and dianionic forms. ...Calculations of the magnetic dipole transition moments have also been carried out at the algebraic diagrammatic construction (ADC(2)) and the second-order approximate coupled-cluster (CC2) levels. The calculations show that the degree of aromaticity and the size of the magnetic dipole transition moment of the lowest magnetic-dipole allowed excited state are related. We show that neutral hetero8circulenes are weakly antiaromatic when the first excited state with a large magnetic dipole transition moment of 10-16 a.u. lies at high energies (∼2.8-3.5 eV). For the dications, this transition often lies at much lower energies. Hetero8circulene dications with large magnetic dipole transition moments are strongly antiaromatic. The lowest excited states of the hetero8circulene dianions have very small magnetic dipole transition moments implying that they are aromatic.
The electronic structure, absorption and emission spectra, aromaticity and photophysical behavior of the recently synthesized tetrasilatetrathia8circulene and tetragermatetrathia8circulene compounds ...have been studied computationally. Both compounds demonstrate a specific bifacial aromaticity, which is unusual for hetero8circulenes; the inner eight-membered core sustains an expected strong paratropic magnetically-induced ring current, while the outer perimeter contains saturated Si(Et)2 and Ge(Et)2 moieties which break the conjugation between the thiophene rings. The overall magnetically-induced ring current for both studied circulenes is close to zero because of the strong local diatropic currents in each thiophene ring that compensate the paratropic counterpart. The electronic absorption and emission spectra of tetrasilatetrathia8circulene and tetragermatetrathia8circulene demonstrate a clear visible vibronic progression. The 0-0 band is the most active one in the absorption spectra, while in the fluorescence spectra the 0-1 band composed of several normal vibrations is more intense compared with the 0-0 band in excellent agreement with experiment. Accounting for spin-orbit coupling effects, an analysis of the photophysical constants for the two compounds demonstrates: (1) a clear manifestation of the internal heavy atom effect on the inter-system crossing efficiency; (2) one to two order domination of non-radiative rates over the fluorescence rate; and (3) that the S1-S0 internal conversion is extremely slow and can not compete with the fluorescence, while the S1-Tn inter-system crossing is a main deactivation channel of the S1 excited state. These results provide new insight into the electronic structure and photophysics of tetrasilatetrathia8circulene and tetragermatetrathia8circulene as novel standalone representatives of hetero8circulenes - tetraannelated derivatives of tetrathienylene.
The present review highlights recent advances in experimental and theoretical chemistry dealing with investigation of the electronic structures and physicochemical properties of hetero8circulenes. ...These compounds are the only representatives of planar heteroannulated cyclooctatetraenes. It is shown that high molecular symmetry of hetero8circulenes and the extended specific -conjugated chain are the main factors responsible for high stability of the crystal packing modes and the optical and magnetic properties of these compounds. These effects also determine numerous selection rules for electronic and vibrational transitions in UV-Vis, IR and Raman spectra. Emphasis is given to the aromaticity of hetero8circulenes containing the inner antiaromatic cyclooctatetraene core. The planar structure of the latter is stabilized by a polyaromatic system composed of benzene rings and five-membered heterocycles. Due to high thermal and chemical stability of most hetero8circulenes combined with semiconducting properties, these compounds can be considered as promising materials for molecular electronics and nanophotonics, in particular for the production of organic light-emitting diodes and field-effect transistors. The bibliography includes 154 references.
The software and hardware tools for the instrumental estimation and control of the geomechanical state of engineering facilities are presented. A description of the proposed technique for measuring ...radial and longitudinal displacements of check borehole contour is given. A research methodology and interpretation of experimental data with analysis and monitoring of the stress-strain state of engineering facilities are proposed. The results of testing the developed software and hardware in the conditions of industrial enterprises are presented.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A series of planar hetero8circulenes and their doubly charged ions are studied by the NICS and GIMIC methods to interpret the aromatic properties of these high symmetry species. In accordance with ...the performed calculations all studied hetero8circulenes are found to be nonaromatic compounds because paratropic and diatropic ring-currents are completely canceled yielding almost zero net current. In great contrast, the dicationic and dianionic hetero8circulenes demonstrate the predominant contribution of diatropic ring currents resulting in the total aromatic character of the studied doubly charged ions. This fact allows us to predict the high stability of dianionic hetero8circulenes and explains the extremely high stability of dicationic species observed in the mass-spectra.
Tests of a developed system for measuring deviation of drill holes reveal its shortcomings. Regarding subhorizontal holes, the key problem is measurement of inclinations and deviations from vertical ...line at a huge number of points (up to 200) by the measuring device moving inside a casing string to 100 m long. The authors analyze influence of different-type data channels on reliability, accuracy and stability of the data recording in the system based on analog and digital signal converters. Applicability of liquid and solid-state integral deviation sensors for pointing of the down-the-hole measuring device is discussed. The paper proposes to use digital microprocessor methods for measuring and converting signals with software support at the upper and lower levels of the deviation determination system.
Secondary electron emission is the most important stage in the mechanism of radiation damage to DNA biopolymers induced by primary ionizing radiation. These secondary electrons ejected by the primary ...electron impacts can produce further ionizations, initiating an avalanche effect, leading to genome damage through the energy transfer from the primary objects to sensitive biomolecular targets, such as nitrogenous bases, saccharides, and other DNA and peptide components. In this work, the formation of positive and negative ions of purine bases of nucleic acids (adenine and guanine molecules) under the impact of slow electrons (from 0.1 till 200 eV) is studied by the crossed electron and molecular beams technique. The method used makes it possible to measure the molecular beam intensity and determine the total cross-sections for the formation of positive and negative ions of the studied molecules, their energy dependences, and absolute values. It is found that the maximum cross section for formation of the adenine and guanine positive ions is reached at about 90 eV energy of the electron beam and their absolute values are equal to 2.8 × 10(-15) and 3.2 × 10(-15) cm(2), respectively. The total cross section for formation of the negative ions is 6.1 × 10(-18) and 7.6 × 10(-18) cm(2) at the energy of 1.1 eV for adenine and guanine, respectively. The absolute cross-section values for the molecular ions are measured and the cross-sections of dissociative ionization are determined. Quantum chemical calculations are performed for the studied molecules, ions and fragments for interpretation of the crossed beams experiments.
The trials of the automated stress measurement equipment have revealed the necessity to upgrade its component represented by the borehole strainmeter. Application of the digital microprocessing ...methods for signal measurement and conversion has allowed elimination of negative impacts and enhanced efficiency and reliability of stress-strain control in rocks.
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