| 1. |
- Aamodt, K., et al.
(author)
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The ALICE experiment at the CERN LHC
- 2008
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In: Journal of Instrumentation. - 1748-0221. ; 3:S08002
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Research review (peer-reviewed)abstract
- ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries, Its overall dimensions are 16 x 16 x 26 m(3) with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008.
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| 2. |
- Baryshnikov, Gleb V., et al.
(author)
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A computational study of aromaticity and photophysical properties of unsymmetrical azatrioxa[8]circulenes
- 2017
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In: New Journal of Chemistry. - : Royal Society of Chemistry. - 1144-0546 .- 1369-9261. ; 41:7, s. 2717-2723
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Journal article (peer-reviewed)abstract
- Owing to their potential use in organic light-emitting diodes and field-effect transistors we present a theoretical study of a series of unsymmetrical azatrioxa[8]circulenes in order to explain the impact of outer substituents and benzoannelation on photophysical constants and aromaticity of these compounds in terms of spin-orbit coupling perturbation and magnetically-induced ring currents. It is argued that the S1-Tn inter-system crossing processes constitute the main deactivation pathways for the fluorescence quenching, something that is supported by a good agreement obtained with experimental data on fluorescence quantum yields. The concept of the gauge-including magnetically induced currents has been applied in order to estimate the role of substituents and benzoannelated fragments on the aromaticity and particularly on the overall balance between the diatropic “aromatic” and paratropic “antiaromatic” current strengths. While a variation of the substituents in the outer perimeter of the studied circulenes does not provide a clear effect on their aromaticity, it is demonstrated that an additional benzoannelation (π-extension) of the azatrioxa[8]circulene macrocycle induces a significant aromaticity enhancement.
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| 3. |
- Baryshnikov, Gleb V., et al.
(author)
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Aromaticity and photophysics of tetrasila- and tetragerma-annelated tetrathienylenes as new representatives of the hetero[8]circulene family
- 2019
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 21:18, s. 9246-9254
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Journal article (peer-reviewed)abstract
- The electronic structure, absorption and emission spectra, aromaticity and photophysical behavior of the recently synthesized tetrasilatetrathia[8]circulene and tetragermatetrathia[8]circulene compounds have been studied computationally. Both compounds demonstrate a specific bifacial aromaticity, which is unusual for hetero[8]circulenes; 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 tetrasilatetrathia[8]circulene and tetragermatetrathia[8]circulene 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 S-1-S-0 internal conversion is extremely slow and can not compete with the fluorescence, while the S-1-T-n inter-system crossing is a main deactivation channel of the S-1 excited state. These results provide new insight into the electronic structure and photophysics of tetrasilatetrathia[8]circulene and tetragermatetrathia[8]circulene as novel standalone representatives of hetero[8]circulenes - tetraannelated derivatives of tetrathienylene.
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| 4. |
- Baryshnikov, Gleb V., et al.
(author)
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Aromaticity of the doubly charged [8]circulenes
- 2016
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:13, s. 8980-8992
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Journal article (peer-reviewed)abstract
- Magnetically induced current densities and current pathways have been calculated for a series of fully annelated dicationic and dianionic tetraphenylenes, which are also named [8]circulenes. The gauge including magnetically induced current (GIMIC) method has been employed for calculating the current density susceptibilities. The aromatic character and current pathways are deduced from the calculated current density susceptibilities showing that the neutral [8]circulenes have two concentric pathways with aromatic and antiaromatic character, respectively. The inner octatetraene core (the hub) is found to sustain a paratropic (antiaromatic) ring current, whereas the ring current along the outer part of the macrocycle (the rim) is diatropic (aromatic). The neutral [8]circulenes can be considered nonaromatic, because the sum of the ring-current strengths of the hub and the rim almost vanishes. The aromatic character of the doubly charged [8]circulenes is completely different: the dianionic [8]circulenes and the OC-, CH-, CH2-, SiH-, GeH-, SiH2-, and GeH2-containing dicationic species sustain net diatropic ring currents i.e., they are aromatic, whereas the O-, S-, Se-, NH-, PH- and AsH-containing dicationic [8]circulenes are strongly antiaromatic. The present study also shows that GIMIC calculations on the [8]circulenes provide more accurate information about the aromatic character than that obtained using local indices such as nuclear-independent chemical shifts (NICSs) and H-1 NMR chemical shifts.
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| 5. |
- Baryshnikov, Gleb V., et al.
(author)
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Benzoannelated aza-, oxa- and azaoxa[8]circulenes as promising blue organic emitters
- 2016
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In: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 18:40, s. 28040-28051
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Journal article (peer-reviewed)abstract
- In the present work, we studied the synergetic effect of benzoannelation and NH/O-substitution for enhancing the absorption intensity in a series of novel designed benzoannelated aza- and oxa[8]circulenes. Semi-empirical estimations of the fluorescence rate constants allowed us to determine the most promising fluorophores among all the possible benzoannelated aza-, oxa- and mixed azaoza[8]circulenes. Among them, para-dibenzoannelated [8]circulenes demonstrated the most intense light absorption and emission due to the prevailing role of the linear acene chromophore. Calculated phi(fl) values are in complete agreement with experimental data for a number of already synthesized circulenes. Thus, we believe that the most promising circulenes designed in this study can demonstrate an intensive fluorescence in the case of their successful synthesis, which in turn could be extremely useful for the fabrication of future blue OLEDs. Special attention is devoted to the aromaticity features and peculiarities of the absorption spectra for the two highly-symmetrical (D-4h ground state symmetry) pi-isoelectronic species as well as the so-called tetrabenzotetraaza[8]circulene and tetrabenzotetraoxa[8]circulene molecules. Both of them are characterized by rich electronic spectra, which can be assigned only by taking into account the vibronic coarse structure of the first electronic absorption band; the 0-1 and 0-2 transitions were found to be active in the absorption spectrum in complete agreement with experimental data obtained for both energy and intensity. The corresponding promotive vibrational modes have been determined and their vibronic activity estimated using the Franck-Condon approximation.
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| 6. |
- Baryshnikov, Gleb V., et al.
(author)
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Optical tuning of tetrabenzo[8]circulene derivatives through pseudorotational conformational isomerization
- 2018
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In: Dyes and pigments. - : Elsevier. - 0143-7208 .- 1873-3743. ; 151, s. 372-379
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Journal article (peer-reviewed)abstract
- In order to further search efficient [8]circulene materials for OLED applications we have theoretically investigated the structure and electronic, absorption spectra of functionalized tetrabenzo[8]circulenes with different substituents in the outer perimeter. These hydrocarbon materials complement the wide family of [8]circulenes which earlier have been demonstrated to possess promising emissive and exciplex-forming properties suitable for organic light emitting diodes. The hydrocarbon tetrabenzo[8]circulenes show saddle shape of the molecular skeleton which can exist in two different conformations with different curvatures of the macrocycle. The aromaticity, electronic structure and orbital pattern are found to be principally different for these two isomers, where the global minimum isomer is weakly antiaromatic and electronically less stable comparing with the non-aromatic local minimum structure. The absorption spectra are also very different: the global minimum structure is more active in the long-wavelength region while the local minimum isomer shows absorption only at short wavelengths. Our computational findings suggest a new concept for optical tuning of curved [8]circulenes through conformational isomerization and aromaticity control, thus through structural variations without changing the molecular composition. Based on this principle we have designed novel functionalized [8]circulenes with promising fluorescence activity.
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| 7. |
- Baryshnikov, Gleb V., et al.
(author)
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Substituent-sensitive fluorescence of sequentially N-alkylated tetrabenzotetraaza[8]circulenes
- 2017
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In: New Journal of Chemistry. - : Royal Society of Chemistry. - 1144-0546 .- 1369-9261. ; 41:15, s. 7621-7625
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Journal article (peer-reviewed)abstract
- We explore the use of substituent-sensitive balance between fluorescence and non-radiative decay as a tool for optical tuning of promising materials for organic light emitting diode applications. A series of N-butylated tetrabenzotetraaza[8]circulenes is studied computationally in order to explain the gradual decrease of fluorescence intensity with the increase of the substituent number. The inter-system crossing probability is found to increase upon the gradual substitution of the circulene macrocycle as a result of the decrease of the S-1-T-1 energy gap due to the deformation of the tetrabenzotetraaza[8] circulenes and therefore the distortion of the pi-conjugation within the macrocycles. In contrast, the S-1-T-1 spin-orbit coupling matrix elements are quite insensitive to the number of outer substituents. As a result, the fluorescence-responsible pi pi(star) transition becomes less intense and the fluorescence rate constant decreases.
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| 8. |
- Baryshnikov, Gleb V., et al.
(author)
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Vibronic absorption spectra of the angular fused bisindolo- and biscarbazoloanthracene blue fluorophores for OLED applications
- 2018
-
In: Chemical Physics. - : Elsevier. - 0301-0104 .- 1873-4421. ; 513, s. 105-111
-
Journal article (peer-reviewed)abstract
- An in-depth analysis of the vibronic absorption spectra for the recently synthesized blue-fluorescent OLED emitters bis[(1,2)(5,6)]indoloanthracene and biscarbazolo[3,4-a:3',4'-h]anthracene has been carried out computationally at the density functional theory level within the Franck-Condon approximation. These molecules are characterized by extended and rich electronic absorption spectra with most absorption bands being of vibronic origin. The first excited singlet state of bis[(1,2)(5,6)]indoloanthracene compound demonstrates a clear observable double-peak vibronic progression for two different active modes in the absorption spectrum, while the S-2 state is vibronically inactive. In contrast, for the larger biscarbazolo[3,4-a:3',4'-h]anthracene compound the S-0 -> S-2 transition demonstrates well-resolved intense vibronic bands which overlap the less intense progressions of few modes in the S-0 -> S-1 transition. We have also found, that even the higher-lying and very intense S-0 -> S-4 and S-0 -> S-5 transitions for bis[(1,2)(5,6)]indoloanthracene and biscarbazolo[3,4-a:3',4'-h]anthracene, respectively, are characterized by clear vibronic progressions in excellent agreement with experimental spectra.
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| 9. |
- Karaush-Karmazin, Nataliya N., et al.
(author)
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Impact of heteroatoms (S, Se, and Te) on the aromaticity of heterocirculenes
- 2019
-
In: New Journal of Chemistry. - : ROYAL SOC CHEMISTRY. - 1144-0546 .- 1369-9261. ; 43:30, s. 12178-12190
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Journal article (peer-reviewed)abstract
- A series of thia[7]circulenes and novel Se-, Te-, S/Te-, and Se/Te-substituted [8]circulenes have been studied by calculations of nucleus-independent chemical shift indices and gauge including magnetically induced currents to interpret the impact of heteroatoms on the aromatic properties of these polyheterocyclic species. The calculations indicate that all the studied hetero[7]circulenes and hetero[8]circulenes consist of two concentric subsystems: an inner seven- or eight-membered core is antiaromatic because of the existence of a paratropic ring current, and an outer system of benzene and hetarene rings that exhibit aromatic behaviour due to the circulation of diatropic ring currents. Thus, most of the hetero[7]circulenes can be considered as slightly antiaromatic because of the slight domination of the paratropic ring currents over the diatropic ones, whereas hetero[8]circulenes represent aromatic species due to the prevailing contribution of the diatropic currents. The antiaromaticity gradually increases with more scattered arrangements of the thiophene and benzene rings in each series of di-, tri-, tetra-, and pentathia[7]circulenes because of the reduced conjugation effect between the neighboring thiophene and benzene rings. Loss of planarity with increased strain leads to an increased antiaromatic character of the lower representatives of the thia[n]circulenes, whereas higher thia[n]circulenes demonstrate a more pronounced aromatic nature because of the small deviation from planarity. The ring current topology is found to be quite insensitive to the heteroatom type, number of hetarene rings and the size of the inner ring; this clearly manifests the special electronic structure of hetero[n]circulenes containing two concentric cyclic subsystems.
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| 10. |
- Karaush, Nataliya N., et al.
(author)
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DFT simulation of the heteroannelated octatetraenes vibronic spectra with the Franck-Condon and Herzberg-Teller approaches including Duschinsky effect
- 2015
-
In: Chemical Physics. - : Elsevier. - 0301-0104 .- 1873-4421. ; 459, s. 65-71
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Journal article (peer-reviewed)abstract
- Calculations of vibronic structure in the electronic absorption spectra are carried out for the series of heteroannelated octatetraenes on the basis of density functional theory method. Both Franck-Condon and Herzberg-Teller approaches have been used for estimation of frequency and intensity of vibronic bands in the simulated absorption spectra with respect to the S-0 -> S-1 electronic transition. The key result discussed in this work is that the electronic transition into the first singlet excited states is vibronicallyactive in the absorption spectra for all studied circulenes in a good agreement with experimental observations. We have confirmed our previous assumption that the first (low-lying) weak absorption maximum in the spectra of tetra-tert-butyltetraoxa[8] circulene and dithieno[3,4-b: 3',4'-d]thiophene-annelated cyclooctatetraene can be assigned just for the S-0 -> S-1 transition which produce the next more intense vibronic satellite. In the case of aza[8] circulenes the S-0 -> S-1 transition is symmetry allowed and the corresponding vibronic bands are less intense relative to 0-0 band. (C) 2015 Elsevier B.V. All rights reserved.
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