| 1. |
- Aidas, Kestutis, et al.
(författare)
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The Dalton quantum chemistry program system
- 2014
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Ingår i: WIREs Computational Molecular Science. - : Wiley. - 1759-0876 .- 1759-0884. ; 4:3, s. 269-284
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Tidskriftsartikel (refereegranskat)abstract
- Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree-Fock, Kohn-Sham, multiconfigurational self-consistent-field, MOller-Plesset, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic-structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge-origin-invariant manner. Frequency-dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one-, two-, and three-photon processes. Environmental effects may be included using various dielectric-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from for a number of UNIX platforms.
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| 2. |
- Brinne Roos, Johanna, 1976-
(författare)
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Electron Recombination with Small Molecular Ions
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis I have theoretically studied electron recombination processes with small molecular ions. In these kind of processes resonant states are involved. To calculate the potential energy for these states as a function of internuclear distance, structure calculations and scattering calculations have to be performed. So far I have been studying the ion-pair formation with in electron recombination with H3+. The cross section for this process has been calculated using different kind of models, both a time dependent quantum mechanical and a semiclassical. I have also studied the direct process of dissociative recombination of HF+. To calculate the total cross section for this process, we have performed wave packet propagation on thirty resonant states and summed up the individual cross sections for these states. The cross sections for both these processes have a similar appearance to those measured experimentally in the ion storage ring CRYRING in Stockholm.
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| 3. |
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| 4. |
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| 5. |
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| 6. |
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| 7. |
- Adranno, Brando, et al.
(författare)
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The 8-hydroxyquinolinium cation as a lead structure for efficient color-tunable ionic small molecule emitting materials
- 2023
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Ingår i: Advanced Photonics Research. - : John Wiley & Sons. - 2699-9293. ; 4:3
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Tidskriftsartikel (refereegranskat)abstract
- Albeit tris(8-hydroxyquinolinato) aluminum (Alq3) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand-centered states, the use of metal-free 8-hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8-hydroxyquinolinium cations into a solid rigid network with appropriate counter-anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as pi-stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue-green (488 nm). Time-dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long-lived S-1 level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq3 and related materials, both as solids and thin films with quantum yields (QYs) up to 40-50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 °C.
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| 8. |
- Aidas, Kestutis, et al.
(författare)
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A quantum mechanics/molecular dynamics study of electric field gradient fluctuations in the liquid phase. The case of Na+ in aqueous solution
- 2013
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 15:5, s. 1621-1631
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Tidskriftsartikel (refereegranskat)abstract
- The Na-23 quadrupolar coupling constant of the Na+ ion in aqueous solution has been predicted using molecular dynamics simulations and hybrid quantum mechanics/molecular mechanics methods for the calculation of electric field gradients. The developed computational approach is generally expected to provide reliable estimates of the quadrupolar coupling constants of monoatomic species in condensed phases, and we show here that intermolecular polarization and non-electrostatic interactions are of crucial importance as they result in a 100% increased quadrupolar coupling constant of the ion as compared to a simpler pure electrostatic picture. These findings question the reliability of the commonly applied classical Sternheimer approximation for the calculations of the electric field gradient. As it can be expected from symmetry considerations, the quadrupolar coupling constants of the 5- and 6-coordinated Na+ ions in solution are found to differ significantly.
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| 9. |
- Aidas, Kestutis, et al.
(författare)
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Photoabsorption of Acridine Yellow and Proflavin Bound to Human Serum Albumin Studied by Means of Quantum Mechanics/Molecular Dynamics
- 2013
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 117:7, s. 2069-2080
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Tidskriftsartikel (refereegranskat)abstract
- Attempting to unravel mechanisms in optical probing of proteins, we have performed pilot calculations of two cationic chromophores-acridine yellow and proflavin-located at different binding sites within human serum albumin, including the two primary drug binding sites as well as a heme binding site. The computational scheme adopted involves classical molecular dynamics simulations of the ligands bound to the protein and subsequent linear response polarizable embedding density functional theory calculations of the excitation energies. A polarizable embedding potential consisting of point charges fitted to reproduce the electrostatic potential and isotropic atomic polarizabilities computed individually for every residue of the protein was used in the linear response calculations. Comparing the calculated aqueous solution-to-protein shifts of maximum absorption energies to available experimental data, we concluded that the cationic proflavin chromophore is likely not to bind albumin at its drug binding site I nor at its heme binding site. Although agreement with experimental data could only be obtained in qualitative terms, our results clearly indicate that the difference in optical response of the two probes is due to deprotonation, and not, as earlier suggested, to different binding sites. The ramifications of this finding for design of molecular probes targeting albumin or other proteins is briefly discussed.
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| 10. |
- Aklillu, Eleni, et al.
(författare)
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Association of MAOA gene functional promoter polymorphism with CSF dopamine turnover and atypical depression.
- 2009
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Ingår i: Pharmacogenetics and genomics. - 1744-6872. ; 19:4, s. 267-75
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Monoamine oxidase-A (MAO-A) is a key mitochondrial enzyme that metabolizes biogenic amine neurotransmitters such as dopamine and serotonin. Individuals with atypical depression (AD) are particularly responsive to treatment with MAO inhibitors (MAOIs). Biomarker tests are essential for prompt diagnosis of AD, and to identify those with an altered brain neurotransmitter metabolism who may selectively respond to MAOI therapy. METHODS: In a sample of 118 Scandinavian patients with treatment-resistant depression who are naive to MAOI therapy, we investigated the associations between a common MAOA functional promoter polymorphism (MAOA-uVNTR), cerebrospinal fluid (CSF) neurotransmitter metabolites, and AD susceptibility. The metabolites for dopamine (homovanillic acid, HVA), serotonin (5-hydroxyindoleacetic acid) and noradrenaline (3-methoxy-4-hydroxyphenylglycol) were measured in the CSF. RESULTS: AD was associated with the female sex and a higher HVA in CSF (P=0.008). The carriers of the MAOA-uVNTR short allele were significantly overrepresented among women with AD (P=0.005; odds ratio=4.76; 95% confidence interval=1.5-13.1; statistical power=80.0%). Moreover, the MAOA-uVNTR genotype significantly influenced the HVA concentration (P=0.01) and showed a strong trend in relation to 5-hydroxyindoleacetic acid concentration (P=0.057) in women. The mediational statistical analyses showed the CSF-HVA concentration as a key driver of the relationship between MAOA-uVNTR genotype and AD. CONCLUSION: The association of the MAOA-uVNTR with both susceptibility to AD and dopamine metabolite (HVA) concentration lends further biological plausibility for high MAO-A enzyme activity as a mechanistic factor for genetic predisposition to AD through altered dopamine turnover. Our observations provide new evidence on the in-vivo functional significance of the MAOA-uVNTR short allele as a high activity variant.
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| 11. |
- Aldongarov, Anuar, et al.
(författare)
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Theoretical study on passivation of small CdS clusters
- 2014
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Ingår i: Molecular Physics. - : Taylor & Francis. - 0026-8976 .- 1362-3028. ; 112:5-6, s. 674-682
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Tidskriftsartikel (refereegranskat)abstract
- We use density functional theory quantum chemical calculations to model optical properties of small cadmium sulphide clusters in order to explore the formation of trap states and the possibility to achieve surface passivation. The addition of capping oxygen ions on the surface of the CdS quantum dots is found to passivate the single-bonded Cd atoms. Added Cu ions resulted in the formation of deep trap states for certain locations of the copper impurity, while removal of single-bonded Cd atoms by adding S or SH groups leads to a band gap increase.
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| 12. |
- An, Dong, et al.
(författare)
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NIR-II Responsive Inorganic 2D Nanomaterials for Cancer Photothermal Therapy : Recent Advances and Future Challenges
- 2021
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Ingår i: Advanced Functional Materials. - : John Wiley & Sons. - 1616-301X .- 1616-3028. ; 31:32
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Forskningsöversikt (refereegranskat)abstract
- Non-invasive cancer photothermal therapy (PTT) is a promising replacement for traditional cancer treatments. The second near-infrared region induced PTT (NIR-II PTT, 1000-1500 nm) with less energy dissipation has been developed for deeper-seated tumor treatment in recent years compared with the traditional first near-infrared light (750-1000 nm). In addition, the use of emerging inorganic 2D nanomaterials as photothermal agents (PTAs) further enhanced PTT efficiency due to their intrinsic photothermal properties. NIR-II light stimulated inorganic 2D nanomaterials for PTT is becoming a hot topic in both academic and clinical fields. This review summarizes the categories, structures, and photothermal conversion properties of inorganic 2D nanomaterials for the first time. The recent synergistic strategies of NIR-II responsive PTT combined with other treatment approaches including chemotherapy, chemodynamic therapy, photodynamic therapy, radiotherapy are summarized. The future challenges and perspectives on these 2D nanomaterials for NIR-II responsive PTT systems construction are further discussed.
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| 13. |
- Andersson, Egil, 1981-, et al.
(författare)
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Core-valence double photoionization of the CS2 molecule
- 2010
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:9, s. 94305-
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Tidskriftsartikel (refereegranskat)abstract
- Double photoionization spectra of the CS2 molecule have been recorded using the TOF-PEPECO technique in combination with synchrotron radiation at the photon energies h nu=220, 230, 240, 243, and 362.7 eV. The spectra were recorded in the S 2p and C 1s inner-shell ionization regions and reflect dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. MCSCF calculations were performed to model the energies of the dicationic states. The spectra associated with a S 2p vacancy are well structured and have been interpreted in some detail by comparison to conventional S 2p and valence photoelectron spectra. The lowest inner-shell-valence dicationic state is observed at the vertical double ionization energy 188.45 eV and is associated with a (2p(3/2))(-1)(2 pi(g))(-1) double vacancy. The spectrum connected to the C 1s vacancy shows a distinct line at 310.8 eV, accompanied by additional broad features at higher double ionization energies. This line is associated with a (C 1s)(-1)(2 pi(g))(-1) double vacancy. (C-) 2010 American Institute of Physics. [doi: 10.1063/1.3469812]
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| 14. |
- Andersson, Egil, et al.
(författare)
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Single-photon core-valence double ionization of molecular oxygen
- 2008
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 78, s. 023409-
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Tidskriftsartikel (refereegranskat)abstract
- Single-photon core-valence double ionization of molecular oxygen has been studied using a magnetic bottle time-of-flight electron coincidence spectrometer. The K-1V-1 double ionization electron spectrum of O-2 is reported and is assigned with the aid of ab initio calculations. A direct comparison of the core-valence double ionization electron spectra with the conventional valence band photoelectron spectrum is made. The lowest core-valence double ionization energy is found to be 571.6 eV and is associated with a (3)Pi dicationic state.
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| 15. |
- Araya, Mesfin, 1954-
(författare)
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Postconflict internally displaced persons in Ethiopia : mental distress and quality of life in relation to traumatic life events, coping strategy, social support, and living conditions
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: There are about 23.7 million internally displaced persons worldwide today, still living in the low-income countries. Ethiopia has for the past four decades been ravaged by war and famine. A lengthy civil war resulted in Eritrea, formerly a part of Ethiopia, becoming an independent state in 1991. This war led to displacement of one million people, and currently there are about 55000 internally displaced Ethiopians in Addis Ababa, most of them living in temporary shelters. A minority resettled in a small town Debre Zeit south east of Addis Ababa, dispersed in the community. Objectives: To study the consequences of trauma and extreme stress among these displaced persons. Methods: A random sample of 1200 displaced persons was selected from the Kaliti and Kore shelters of Addis Ababa, aged between 18 and 60 years. They were interviewed by internationally validated instruments which were translated into the Ethiopian official language Amharic. Information thus obtained covered sociodemographics, childhood trauma, traumatic life events, and mental distress as assessed by the SCL-90-R, the four domains of quality of life assessed by WHOQOL-BREF, coping strategies, perceived social support, and basic living conditions. A sample of 120 subjects from the displaced persons living in Debre Zeit was similarly evaluated. A study comparing prevalence rates and risk factors for PTSD in four postconflict, low-income countries (Algeria, Cambodia, Ethiopia, Gaza) was also undertaken. Results: Men, compared to women, reported significantly higher experience of trauma, higher perceived social support, and higher task-oriented coping. Women reported higher emotion-oriented coping. In both genders, emotion-oriented coping was correlated with higher trauma events, and task-oriented coping was correlated with higher perceived social support. Mental distress increased and quality of life decreased with age. Mental distress mediated the effects of most trauma in reducing quality of life, and some trauma reduced quality of life directly. Living conditions were also significantly related to quality of life. Coping strategies and perceived social support influenced mental distress and quality of life directly as well as indirectly by moderation, in part gender specific. Placement in the community setting of Debre Zeit gave a better quality of life compared to placement in the shelters of Addis Ababa. This difference was accounted for by the difference in living conditions, particularly protection from animals (rodents) and insects (mosquitoes), for three domains of quality of life. For domain 3 (social relationships), however, several further factors accounted for the difference, like marital status, ethnic belonging and coping strategy. The comparative study of 4 postconflict countries contributes to the theory that trauma may be the direct cause of the onset of PTSD but that a multiplicity of other adverse events determine the development of this disorder. Conclusions: Using the same assessment methods, a wide range of rates of symptoms of PTSD were found among 4 low-income populations who have experienced war, conflict, or mass violence. In the Ethiopian context we also found gender differences in the trauma background, coping strategies and perceived social support. Mental distress mediated much of the effects of trauma on quality of life. Coping strategies and perceived social support were significant moderators in this process.
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| 16. |
- Arul Murugan, N., et al.
(författare)
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Unusual binding-site-specific photophysical properties of a benzothiazole-based optical probe in amyloid beta fibrils
- 2018
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : The Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 20:31, s. 20334-20339
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Tidskriftsartikel (refereegranskat)abstract
- Optical imaging of amyloid fibrils serves as a cost-effective route for the diagnosis of Alzheimer-like conformational diseases. However{,} the challenge here is to optimize the binding affinity and photophysical properties of the optical imaging agents in a way specific to certain types of amyloids. In a few occasions it is shown that novel optical imaging agents can be designed to bind to a particular type of amyloid fibril with larger binding affinity and specificity. There is also a recent report on photoluminescent polythiophenes which display photophysical properties that can be used to distinguish the variants or subtypes of amyloids (J. Rasmussen et al.{,} Proc. Natl. Acad. Sci. U. S. A.{,} 2017{,} 114(49){,} 13018–13023). Based on a multiscale modeling approach{,} here{,} we report on the complementary aspect that the photophysical properties of a benzothiazole based optical probe (referred to as BTA-3) can be specific to the binding sites in the same amyloid fibrils and we attribute this to its varying electronic structure in different sites. As reported experimentally from competitive binding assay studies for many amyloid staining molecules and tracers{,} we also show multiple binding sites in amyloid fibrils for this probe. In particular{,} BTA-3 displayed a red-shift in its low-frequency absorption band only in site-4{,} a surface site of amyloid fibrils when compared to the spectra in water solvent. In the remaining sites{,} it exhibited a less significant blue shift for the same absorption band.
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| 17. |
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| 18. |
- Backlund, Lena, et al.
(författare)
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Identifying predictors for good lithium response - A retrospective analysis of 100 patients with bipolar disorder using a life-charting method.
- 2009
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Ingår i: European psychiatry : the journal of the Association of European Psychiatrists. - : Cambridge University Press (CUP). - 0924-9338. ; 24:3, s. 171-7
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: Our aim was to investigate bipolar patients in order to test the validity of various outcome measures and to identify prognostic predictors for pharmacological treatment. MATERIAL AND METHOD: One hundred patients were interviewed using a computerized life-charting program in a descriptive, retrospective analysis. The concept "Burden of illness" was defined as a combination of severity and duration of episodes. Response to treatment was defined as the difference in burden before and after treatment, a low burden during treatment, and freedom of episodes for at least 3 years after insertion of treatment. RESULTS: The absence of mixed episodes and a high initial burden predicted a good response measured as the difference in burden. If remission for 3 years or a low burden during lithium treatment was used, the absence of rapid cycling and of mixed episodes were the most important predictors. The severity of illness before treatment had no impact. DISCUSSION AND CONCLUSION: We suggest the use of absolute measures of severity during treatment as the most appropriate measure of the outcome. Furthermore, our data provide corroboration that treatment with lithium ameliorates the prognosis of the illness, but that mixed episodes and rapid cycling predict a poorer response to lithium.
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| 19. |
- Baev, A., et al.
(författare)
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A quantum mechanical - Electrodynamical approach to nonlinear properties : Application to optical power limiting with platinum-organic compounds
- 2007
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Ingår i: Journal of nonlinear optical physics and materials. - 0218-8635. ; 16:2, s. 157-169
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Tidskriftsartikel (refereegranskat)abstract
- Light propagation in a medium is sensitively dependent on the shape and intensity of the optical pulse as well as on the electronic and vibrational structure of the basic molecular units. We review in this paper the results of systematic studies of this problem for isotropic media. Our theoretical approach - the quantum mechanical-electrodynamical (QMED) approach - is based on a quantum mechanical account of the many-level electron-nuclear medium coupled to a numerical solution of the density matrix and Maxwell's equations. This allows us to accommodate a variety of nonlinear effects which accomplish the propagation of strong light pulses. Particular attention is paid to the understanding of the role of coherent and sequential excitations of electron-nuclear degrees of freedom. The QMED combination of quantum chemistry with classical pulse propagation enables us to estimate the optical transmission from cross sections of multi-photon absorption processes and from considerations of propagation effects, saturation and pulse effects. Results of the theory suggest that in the nonlinear regime, it is often necessary to simultaneously account for coherent one-step and incoherent step-wise multi-photon absorption, as well as for off-resonant excitations even when resonance conditions prevail. The dynamic theory of nonlinear propagation of a few interacting intense light pulses is highlighted here in a study of the optical power limiting with platinum-organic molecular compounds. © World Scientific Publishing Company.
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| 20. |
- Baev, A., et al.
(författare)
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Bi-directional description of amplified spontaneous emission induced by three-photon absorption
- 2005
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 22:2, s. 385-393
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Tidskriftsartikel (refereegranskat)abstract
- A semiclassical dynamic theory of the nonlinear propagation of a few interacting intense light pulses is applied to study the nonlinear counterpropagation of amplified spontaneous emission (ASE) induced by three-photon absorption of short intense laser pulses in a chromophore solution. Several important results from the modeling are reached for the ASE process developing in the regime of strong saturation. Accounting for ASE in both forward and backward directions with respect to the pump pulse results in a smaller efficiency of nonlinear conversion for the forward ASE compared with the case in which forward emission is considered alone, something that results from the partial repump of the absorbed energy to the backward ASE component; the overall efficiency is nevertheless higher than for the forward emission considered alone. The efficiency of nonlinear conversion of the pump energy to the counterpropagating ASE pulses is strongly dependent on the concentration of active molecules so that a particular combination of concentration versus cell length optimizes the conversion coefficient. Under certain specified conditions, the ASE effect is found to be oscillatory; the origin of oscillations is dynamical competition between stimulated emission and off-resonant absorption. This result can be considered one of the possible explanations of the temporal fluctuations of the forward ASE pulse [Nature 415, 767 (2002)].
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| 21. |
- Baev, A., et al.
(författare)
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Doppler interference in dissociative resonant photoemission
- 2002
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 66:2
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Tidskriftsartikel (refereegranskat)abstract
- Resonant photoemission involving dissociative core excited states has been the subject of a great number of experimental and theoretical investigations in recent time. The resonant decay of such dissociating systems has been shown to lead to semiatomic Auger electron emission spectra, with particular angular behavior. In the present paper a detailed theoretical analysis of dissociative resonant photoemission spectra of homonuclear diatomic molecules is presented. The theory addresses both fixed in space and randomly oriented homonuclear molecules and emphasizes the Doppler effect and the role of the interference between channels referring to the Doppler split atomic fragments. It is shown that peaks originating from decay in the atomic fragments can be asymmetric and structured due to the Doppler interference effect. The predicted strong non-Lorentzian behavior of the substructure on the top of the Doppler broadened atomiclike contribution is traced to the interplay between decay channels leading to gerade and ungerade final states. Simulations based on wave-packet theory are compared with experimental data for molecular oxygen. Our numerical simulations of the atomiclike resonance of fixed in space molecules show that the spectral profile is very sensitive to the shape of interatomic potentials of core excited and final states. It is shown that the Doppler effect in the decay spectra depends upon the symmetry of the core excited state.
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| 22. |
- Baev, A., et al.
(författare)
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General theory for pulse propagation in two-photon active media
- 2002
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 117:13, s. 6214-6220
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Tidskriftsartikel (refereegranskat)abstract
- The propagation of laser pulses of different lengths in nonlinear media of organic absorbers is described starting out from a recently suggested dynamical theory for two-photon absorption (TPA) of molecules in solutions [J. Opt. Soc. Am. B 19, 937 (2002)]. The roles of saturation effects and pulse duration on the suppression of TPA are emphasized. The numerical simulations of the pulse propagation are performed for a two-photon active charge transfer molecule using molecular parameters obtained from first principle calculations.
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| 23. |
- Baev, A., et al.
(författare)
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Geometrical information on core-excited states obtained from interference quenching of vibrational states in resonant x-ray photoemission
- 2003
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 67:2
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Tidskriftsartikel (refereegranskat)abstract
- An interference quenching of the m=1 final state vibrational line in the resonant Auger decay of N 1s-->pi(*) core-excited N-2 is observed and analyzed. The intensity ratio between the m=1 and m=0 vibrational levels of the X (2)Sigma(g)(+) final state shows a surprising nonmonotonic variation as a function of frequency detuning, going through a minimum with a complete suppression of m=1. We have developed a simple model which indicates a linear relation between the value of the detuning frequency for this minimum and the equilibrium bond distance of the core-excited state. This implies the possibility of determining the equilibrium bond distances for core-excited states to a high degree of accuracy. Simultaneously with the simple model we present a strict theory of the studied effect. This strict theory allows us to explore the accuracy of determining the bond length of the core-excited state from resonant Auger spectra. We obtain a weak influence of the core-hole lifetime on the determined bond length, whereas the number of intermediate vibrational states accounted for in the numerical simulations seems to be quite important.
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| 24. |
- Baev, A., et al.
(författare)
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Light-matter interaction of strong laser pulses in the micro-, nano-, and picosecond regimes
- 2007
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Ingår i: Materials Research Society Symposium Proceedings. - 9781605604206 ; , s. 12-29
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Konferensbidrag (refereegranskat)abstract
- Light propagation in a medium is sensitively dependent on the shape and intensity of the optical pulse as well as on the electronic and vibrational structure of the basic molecular units. We review in this paper results of systematic studies of this problem for isotropic media. Our theoretical approach-the quantum mechanical-electrodynamical (QMED) approach-is based on a quantum mechanical account of the many-level electron-nuclear medium coupled to a numerical solution of the density matrix and Maxwell s equations. This allows to accommodate a variety of nonlinear effects which accomplish the propagation of strong light pulses. Particular attention is paid to the understanding of the role of coherent and sequential excitations of electron-nuclear degrees of freedom. The QMED combination of quantum chemistry with classical pulse propagation allows to estimate the optical transmission from cross sections of multi-photon absorption processes and from considerations of propagation effects, saturation and pulse effects. Results of the theory suggest that in the nonlinear regime it is often necessary to account simultaneously for coherent one-step and incoherent step-wise multi-photon absorption, as well as for off-resonant excitations even when resonance conditions prevail. The dynamic theory of nonlinear propagation of a few interacting intense light pulses is here highlighted in a study of the optical power limiting with platinum-organic molecular compounds. © 2007 Materials Research Society.
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| 25. |
- Baev, Alexander, et al.
(författare)
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Metaphotonics : An emerging field with opportunities and challenges
- 2015
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Ingår i: Physics reports. - : Elsevier. - 0370-1573 .- 1873-6270. ; 594, s. 1-60
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Forskningsöversikt (refereegranskat)abstract
- Metaphotonics is an emerging multidisciplinary field that deals with manipulation of electro-magnetic fields in nanoengineered (meta)materials using both electric and magnetic interactions and their cross-coupling. It offers unprecedented control of both linear and nonlinear optical functions for applications ranging from optical switching, to negative- and near-zero refractive index metamaterials, to chiral bioimaging, to cloaking. However, realization of such applications requires physics-guided nanoengineering of appropriate artificial media with electro-magnetic properties at visible and infrared wavelengths that are tailored to surpass those of any naturally-occurring material. Here, we review metaphotonics with a broadened vision and scope, introduce potential applications, describe the role of theoretical physics through multiscale modeling, review the materials development and current status, and outline opportunities in this fertile emerging field.
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| 26. |
- Baev, A., et al.
(författare)
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Nonlinear propagation of strong multi-mode fields
- 2003
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 36, s. 3761-3774
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Tidskriftsartikel (refereegranskat)abstract
- We develop a strict theory of nonlinear propagation of few interacting stronglight beams. The key idea of our approach is a self-consistent solution ofthe nonlinear wave equation and the density matrix equations of the materialbeyond the rotatory wave approximation. We assume a Fourier expansion ofthe density matrixwhich goes beyond the conventionalTaylor expansions of thepolarization over the field amplitudeswhich is inadequate for the field strengthsthat we are interested in. Two qualitatively different situations are considered,with and without phase matching. Unlike in our previous paper (Baev et al2003 J. Opt. Soc. Am. B at press) devoted to the three-photon (TP) absorptioninduced upconverted lasing, we obtain here a strict solution for the nonlinearinteraction between different light beams. The general theory is applied to anumerical study of the role of saturation in TP photoabsorption by an organicchromophore in solution.
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| 27. |
- Baev, Alexander, et al.
(författare)
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Optical limiting properties of Zinc- and Platinum-based organometallic compounds
- 2004
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 108:36, s. 7406-7416
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Tidskriftsartikel (refereegranskat)abstract
- Optical power limiting is theoretically studied using an approach that combines quantum electronic structure calculations of multiphoton excitations and classical calculations of dynamical wave propagation. We illustrate the capability of such a combined approach by presenting results for a couple of organometallic compounds; basic metal-base porphyrins, vinylphenylamine porhyrin, and the so-called type IVc platinum compound. A comparative analysis of their electronic properties related to nonlinear absorption of electromagnetic radiation and their optical limiting capability has been performed based on dynamical simulations of the nonlinear pulse propagation taking account of resonant as well as off-resonant effects. Several key features and rate-limiting steps in the transmission have been examined in relation to various characteristics of the pulse. It is found that the resonant vs off-resonant conditions, the saturation conditions and the dephasing play critical roles for the nonlinear transmission. The saturation effects are sensitive to the pulse duration, the inter-system crossing rate and the quenching of the higher triplet state. The inter-system crossing rate has to be comparable with the inverse pulse duration in order to boost the stepwise two-photon channel associated with singlet-singlet followed by triplet-triplet transitions. It is illustrated that structure-to-property relations of the rate-limiting steps serve as important criteria for choices of compounds suitable for the application of interest.
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| 28. |
- Baev, A, et al.
(författare)
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Picturing molecular femtosecond processes through an ultra-fast controllable X-ray shutter
- 2003
-
Ingår i: Chemical Physics. - 0301-0104 .- 1873-4421. ; 289, s. 51-56
-
Tidskriftsartikel (refereegranskat)abstract
- We show that frequency detuning in a resonant X-ray scattering experiment acts as an X-ray camera shutter by regulating the duration time of the scattering process. The camera shutter can be used to select processes at different time scales for observation. This is illustrated by a resonant Auger study of the ultra-fast dissociation of the core-excited HF molecule. We present experimental results and first principle simulations of the molecular fraction in the resonant Auger spectra of HF which is a dynamical parameter that well illustrates X-ray shutter controlled dissociation.
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| 29. |
- Baev, A., et al.
(författare)
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Quantum-classical modeling of nonlinear pulse propagation in a dissolved two-photon active chromophore
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:11, s. 5379-5385
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Tidskriftsartikel (refereegranskat)abstract
- In the present work we outline the implications of a quantum-classical approach for modeling two-photon absorption of organic chromophores in solution. The approach joins many-photon absorption dynamic simulations with quantum chemical first principles calculations of corresponding excitation energies and transition matrix elements. Among a number of conclusions of the study, we highlight three: (i) The use of either short- or long-pulse excitation is demonstrated to switch the absorptive capacity of the nonlinear medium owing to enhancement of the nonlinear stepwise processes; (ii) The two-photon cross section strongly depends on the way in which the dephasing rate decays when the laser frequency is tuned off-resonant with the corresponding molecular transition; (iii) The results of the pulse propagation simulations based on electronic structure data obtained with a new Coulomb attenuated functional is shown to be in much better agreement with the experimental results than those based on data received with traditional density functionals.
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| 30. |
- Baev, Alexander, et al.
(författare)
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Theoretical Simulations of clamping levels in optical power limiting
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207 .- 1520-5215. ; 110:42, s. 20912-20916
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Tidskriftsartikel (refereegranskat)abstract
- Multiphysics modeling, combining quantum mechanical and classical wave mechanical theories, of clamping levels has been performed for a platinum(II) organic compound in a sol-gel glass matrix. A clamping level of 2.5 mu J is found for a pulse duration of 10 ns. The excited-state absorption in the triplet manifold is shown to be crucial for clamping to occur.
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| 31. |
- Baev, Alexander, et al.
(författare)
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Upconverted lasing based on many-photon absorption : an all dynamic description
- 2004
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 21:2, s. 384-396
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Tidskriftsartikel (refereegranskat)abstract
- A theory is developed for the propagation through a nonlinear medium of strong pump and amplifiedspontaneous-emission pulses. The theory is based on a solution of the density matrix equations that aims at providing an adequate treatment of the nonlinear polarization of the material without addressing the Taylor expansion over the powers of intensity. The theory has been applied for modeling of three-photon absorption induced upconverted stimulated emission of organic molecules in solvents. Numerical results are presented for the organic chromophore 4-[N-(2-hydroxyethyl)-N-(methyl)amino phenyl]-4'-(6-hydroxyhexyl sulfonyl) stilbene dissolved in dimethyl sulfoxide. The results are in good agreement with available experimental results.
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| 32. |
- Bagheri, Niusha, et al.
(författare)
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Change in the emission saturation and kinetics of upconversion nanoparticles under different light irradiations
- 2019
-
Ingår i: Optical materials (Amsterdam). - : Elsevier. - 0925-3467 .- 1873-1252. ; 97
-
Tidskriftsartikel (refereegranskat)abstract
- Nd3+-sensitized upconversion nanoparticles (UCNPs) can be excited by both 980 and 808 nm light, which is regarded as a particularly advantageous property of these particles. In this work, we demonstrate that the nanoparticles can exhibit significantly different response when excited at these two excitation wavelengths, showing dependence on the intensity of the excitation light and the way it is distributed in time. Specifically, with 808 nm excitation saturation in the emitted luminescence is more readily reached with increasing excitation intensities than upon 980 nm excitation. This is accompanied by delayed upconversion luminescence (UCL) kinetics and weaker UCL intensities. The different luminescence response at 808 and 980 nm excitation reported in this work is relevant in a manifold of applications using UCNPs as labels and sensors. This could also open new possibilities for multi-wavelength excitable UCNPs for upconversion color display and in laser-scanning microscopy providing selective readouts and sub-sectioning of samples.
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| 33. |
- Bai, Linyi, et al.
(författare)
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Iron( III)-Quantity-Dependent Aggregation-Dispersion Conversion of Functionalized Gold Nanoparticles
- 2014
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 20:14, s. 4032-4037
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Tidskriftsartikel (refereegranskat)abstract
- Developing gold nanoparticles (AuNPs) with well-designed functionality is highly desirable for boosting the performance and versatility of inorganic-organic hybrid materials. In an attempt to achieve ion recognition with specific signal expressions, we present here 4-piperazinyl-1,8-naphthalimide-functionalized AuNPs for the realization of quantitative recognition of Fe-III ions with dual (colorimetric and fluorescent) output. The research takes advantage of 1)quantity-controlled chelation-mode transformation of the piperazinyl moiety on the AuNPs towards Fe-III, thereby resulting in an aggregation-dispersion conversion of the AuNPs in solution, and 2)photoinduced electron transfer of a naphthaimide fluorophore on the AuNPs, thus leading to reversible absorption and emission changes. The functional AuNPs are also responsive to pH variations. This strategy for realizing the aggregation-dispersion conversion of AuNPs with returnable signal output might exhibit application potential for advanced nanoscale chemosensors.
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| 34. |
- Baidya, Anurag T. K., et al.
(författare)
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Mechanistic Insight into the Inhibition of Choline Acetyltransferase by Proton Pump Inhibitors
- 2023
-
Ingår i: ACS Chemical Neuroscience. - : American Chemical Society (ACS). - 1948-7193. ; 14:4, s. 749-765
-
Tidskriftsartikel (refereegranskat)abstract
- Various pharmacoepidemiological investigational studies have indicated that Proton Pump Inhibitors (PPIs) may increase the likelihood of developing Alzheimer's disease (AD) and non-AD related dementias. Previously, we have reported the inhibition of the acetylcholine biosynthesizing enzyme choline acetyltransferase (ChAT) by PPIs, for which omeprazole, lansoprazole, and pantoprazole exhibited IC50 values of 0.1, 1.5, and 5.3 mu M, respectively. In this study we utilize a battery of computational tools to perceive a mechanistic insight into the molecular interaction of PPIs with the ChAT binding pocket that may further help in designing novel ChAT ligands. Various in-silico tools make it possible for us to elucidate the binding interaction, conformational stability, and dynamics of the protein-ligand complexes within a 200 ns time frame. Further, the binding free energies for the PPI-ChAT complexes were explored. The results suggest that the PPIs exhibit equal or higher binding affinity toward the ChAT catalytic tunnel and are stable throughout the simulated time and that the pyridine ring of the PPIs interacts primarily with the catalytic residue His324. A free energy landscape analysis showed that the folding process was linear, and the residue interaction network analysis can provide insight into the roles of various amino acid residues in stabilization of the PPIs in the ChAT binding pocket. As a major factor for the onset of Alzheimer's disease is linked to cholinergic dysfunction, our previous and the present findings give clear insight into the PPI interaction with ChAT. The scaffold can be further simplified to develop novel ChAT ligands, which can also be used as ChAT tracer probes for the diagnosis of cholinergic dysfunction and to initiate timely therapeutic interventions to prevent or delay the progression of AD.
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| 35. |
- Balamurugan, Kanagasabai, et al.
(författare)
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Effect of Alzheimer Familial Chromosomal Mutations on the Amyloid Fibril Interaction with Different PET Tracers : Insight from Molecular Modeling Studies
- 2017
-
Ingår i: ACS Chemical Neuroscience. - : American Chemical Society (ACS). - 1948-7193. ; 8:12, s. 2655-2666
-
Tidskriftsartikel (refereegranskat)abstract
- Alzheimer's disease (AD) is the most common neurodegenerative disorder. Along with an increasing number of elderly worldwide, it poses a great challenge for the society and health care. Although sporadic AD is the common form of AD, 2-3% of the AD cases are expected to be due to mutations in the fi region of the amyloid precursor protein, which is referred to as autosomal dominant AD (ADAD). These mutations may cause changes in the secondary structure of the amyloid fi fibrils and may alter the fibrillization rate leading to changes in the disease development and could also affect the binding to tracers used in diagnosis. In particular, from some recent clinical studies using PET tracers for detection of fibrillar amyloids, it is evident that in ADAD patients with Arctic mutation no amyloid plaque binding can be detected with the "C Pittsburgh Compound B (C-11-PIB). However, for in vitro conditions, significant binding of H-3-PIB has been reported for the amyloid fibrils carrying the Arctic mutation. The aim of the present study is to investigate if there is any mutation specific binding of commonly used amyloid tracers, namely, florbetaben, florbetapir, FPIB, AZD4694, and AZD2184, by means of molecular modeling techniques. Other than Arctic, ADAD mutations, such as the Dutch, Italian, Iowa, and Flemish mutations, are considered in this study. We report that all tracers except florbetapir show reduced binding affinity toward amyloid beta fibrils with the Arctic mutation when compared to the native type. Moreover, florbetapir is the only tracer that binds to all mutants with increased affinity when compared to the native fibril. The results obtained from these studies could increase the understanding of the structural changes caused by mutation and concomitant changes in the interaction pattern of the PET tracers with the mutated variants, which in turn can be useful in selecting the appropriate tracers for the purpose of diagnosis as well as for designing new tracers with desirable properties.
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| 36. |
- Balamurugan, Kanagasabai, et al.
(författare)
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Multistep Modeling Strategy To Improve the Binding Affinity Prediction of PET Tracers to A beta(42) : Case Study with Styrylbenzoxazole Derivatives
- 2016
-
Ingår i: ACS CHEMICAL NEUROSCIENCE. - : American Chemical Society (ACS). - 1948-7193. ; 7:12, s. 1698-1705
-
Tidskriftsartikel (refereegranskat)abstract
- Positron emission tomography (PET) tracers play an important role in the diagnosis of Alzheimer's disease, a condition that leads to progressive dementia and memory loss. A high binding affinity and specificity of the PET tracers to amyloid oligomers and fibrils are crucial for their successful application as diagnostic agents. In this sense, it is essential to design PET tracers with enhanced binding affinities, which can lead to more precise and earlier detection of Alzheimer's disease conditions. The application of in silico methodology for the design and development of efficient PET tracers may serve as an important route to improved Alzheimer's disease diagnosis. In this work, the performance of widely used computational methods is explored for predicting experimental binding affinities of styrylbenzoxazole (SB) derivatives against a common amyloid protofibril. By performing docking, molecular dynamics, and quantum chemistry calculations in sequence their combined predictive performance is explored. The present work emphasizes the merits as well as limitations of these simulation strategies in the realm of designing PET tracers for Alzheimer's disease diagnosis.
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| 37. |
- Banerjee, Saikat, et al.
(författare)
-
Granular superconductor in a honeycomb lattice as a realization of bosonic Dirac material
- 2016
-
Ingår i: PHYSICAL REVIEW B. - : American Physical Society. - 2469-9950. ; 93:13
-
Tidskriftsartikel (refereegranskat)abstract
- We examine the low-energy effective theory of phase oscillations in a two-dimensional granular superconducting sheet where the grains are arranged in a honeycomb lattice structure. Using the example of graphene, we present evidence for the engineered Dirac nodes in the bosonic excitations: the spectra of the collective bosonic modes cross at the K and K' points in the Brillouin zone and form Dirac nodes. We show how two different types of collective phase oscillations are obtained and that they are analogous to the Leggett and the Bogoliubov-Anderson-Gorkov modes in a two-band superconductor. We show that the Dirac node is preserved in the presence of an intergrain interaction, despite induced changes of the qualitative features of the two collective modes. Finally, breaking the sublattice symmetry by choosing different on-site potentials for the two sublattices leads to a gap opening near the Dirac node, in analogy with fermionic Dirac materials. The Dirac node dispersion of bosonic excitations is thus expanding the discussion of the conventional Dirac cone excitations to the case of bosons. We call this case as a representative of bosonic Dirac materials (BDM), similar to the case of Fermionic Dirac materials extensively discussed in the literature.
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| 38. |
- Banerjee, Saikat, et al.
(författare)
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Interacting Dirac materials
- 2020
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 32:40
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the extent to which the class of Dirac materials in two-dimensions provides general statements about the behavior of both fermionic and bosonic Dirac quasiparticles in the interacting regime. For both quasiparticle types, we find common features for the interaction induced renormalization of the conical Dirac spectrum. We perform the perturbative renormalization analysis and compute the self-energy for both quasiparticle types with different interactions and collate previous results from the literature whenever necessary. Guided by the systematic presentation of our results in table1, we conclude that long-range interactions generically lead to an increase of the slope of the single-particle Dirac cone, whereas short-range interactions lead to a decrease. The quasiparticle statistics does not qualitatively impact the self-energy correction for long-range repulsion but does affect the behavior of short-range coupled systems, giving rise to different thermal power-law contributions. The possibility of a universal description of the Dirac materials based on these features is also mentioned.
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| 39. |
- Banerjee, Saikat, et al.
(författare)
-
Landau-like states in neutral particles
- 2016
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Ingår i: PHYSICAL REVIEW B. - 2469-9950. ; 93:23
-
Tidskriftsartikel (refereegranskat)abstract
- We show the emergence of a new type of dispersion relation for neutral atoms with an interesting similarity to the spectrum of two-dimensional electrons in an applied perpendicular constant magnetic field. These neutral atoms can be confined in toroidal optical traps and give quasi-Landau spectra. In strong contrast to the equidistant infinitely degenerate Landau levels for charged particles, the spectral gap for such two-dimensional neutral particles increases in particular electric-field configurations. The idea in the paper is motivated by the development in cold atom experiments and builds on the seminal paper of Aharonov and Casher.
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| 40. |
- Baryshnikov, Glib, et al.
(författare)
-
Odd-Number Cyclo[n]Carbons Sustaining Alternating Aromaticity
- 2022
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 126:16, s. 2445-2452
-
Tidskriftsartikel (refereegranskat)abstract
- Cyclo[n]carbons (n = 5, 7, 9,..., 29) composed from an odd number of carbon atoms are studied computationally at density functional theory (DFT) and ab initio complete active space self-consistent field (CASSCF) levels of theory to get insight into their electronic structure and aromaticity. DFT calculations predict a strongly delocalized carbene structure of the cyclo[n]carbons and an aromatic character for all of them. In contrast, calculations at the CASSCF level yield geometrically bent and electronically localized carbene structures leading to an alternating double aromaticity of the odd-number cyclo[n]carbons. CASSCF calculations yield a singlet electronic ground state for the studied cyclo[n]carbons except for C25, whereas at the DFT level the energy difference between the lowest singlet and triplet states depends on the employed functional. The BHandHLYP functional predicts a triplet ground state of the larger odd-number cyclo[n]carbons starting from n = 13. Current-density calculations at the BHandHLYP level using the CASSCFoptimized molecular structures show that there is a through-space delocalization in the cyclo[n]carbons. The current density avoids the carbene carbon atom, leading to an alternating double aromaticity of the oddnumber cyclo[n]carbons satisfying the antiaromatic [4k+1] and aromatic [4k+3] rules. C11, C15, and C19 are aromatic and can be prioritized in future synthesis. We predict a bond-shift phenomenon for the triplet state of the cyclo[n]carbons leading to resonance structures that have different reactivity toward dimerization.
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| 41. |
- Baryshnikov, Gleb, et al.
(författare)
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Theory and Calculation of the Phosphorescence Phenomenon
- 2017
-
Ingår i: Chemical Reviews. - : American Chemical Society (ACS). - 0009-2665 .- 1520-6890. ; 117:9, s. 6500-6537
-
Forskningsöversikt (refereegranskat)abstract
- Phosphorescence is a phenomenon of delayed luminescence that corresponds to the radiative decay of the molecular triplet state. As a general property of molecules, phosphorescence represents a cornerstone problem of chemical physics due to the spin prohibition of the underlying triplet-singlet emission and because its analysis embraces a deep knowledge of electronic molecular structure. Phosphorescence is the simplest physical process which provides an example of spin-forbidden transformation with a characteristic spin selectivity and magnetic field dependence, being the model also for more complicated chemical reactions and for spin catalysis applications. The bridging of the spin prohibition in phosphorescence is commonly analyzed by perturbation theory, which considers the intensity borrowing from spin-allowed electronic transitions. In this review, we highlight the basic theoretical principles and computational aspects for the estimation of various phosphorescence parameters, like intensity, radiative rate constant, lifetime, polarization, zero-field splitting, and spin sublevel population. Qualitative aspects of the phosphorescence phenomenon are discussed in terms of concepts like structure-activity relationships, donor-acceptor interactions, vibronic activity, and the role of spin-orbit coupling under charge-transfer perturbations. We illustrate the theory and principles of computational phosphorescence by highlighting studies of classical examples like molecular nitrogen and oxygen, benzene, naphthalene and their azaderivatives, porphyrins, as well as by reviewing current research on systems like electrophosphorescent transition metal complexes, nucleobases, and amino acids. We furthermore discuss modern studies of phosphorescence that cover topics of applied relevance, like the design of novel photofunctional materials for organic light-emitting diodes (OLEDs), photovoltaic cells, chemical sensors, and bioimaging.
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| 42. |
- Baryshnikov, Gleb V., et al.
(författare)
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A computational study of aromaticity and photophysical properties of unsymmetrical azatrioxa[8]circulenes
- 2017
-
Ingår i: New Journal of Chemistry. - : Royal Society of Chemistry. - 1144-0546 .- 1369-9261. ; 41:7, s. 2717-2723
-
Tidskriftsartikel (refereegranskat)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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| 43. |
- Baryshnikov, Glib V., et al.
(författare)
-
A computational study of structural and magnetic properties of bi- and trinuclear Cu(II) complexes with extremely long Cu–-Cu distances
- 2017
-
Ingår i: Chemical Physics. - : Elsevier. - 0301-0104 .- 1873-4421. ; 491, s. 48-55
-
Tidskriftsartikel (refereegranskat)abstract
- Three recently synthesized copper(II) complexes with aroylhydrazones of trifluoroacetic and benzenecarboxylic acids (Dalton Trans., 2013, 42, 16878) have been computationally investigated by density functional theory within the broken symmetry approximation accounting for empirical dispersion corrections. A topological analysis of electron density distributions has been carried out using Bader's “quantum theory of atoms in molecules” formalism. The calculated values of spin-spin exchange for the studied dinuclear complexes indicate a very weak ferromagnetic coupling of the unpaired electrons in good agreement with experimental data. At the same time, the trinuclear copper(II) complex possesses a low-spin doublet ground state with one ferromagnetic and two antiferromagnetic spin projections between the triangular-positioned Cu2+ ions. The estimated values of the coupling constants for the spin-spin exchange in this trinuclear complex are in a good agreement with experimental observations. The calculations support a mechanism of exchange coupling through the aromatic links in these strongly spin-separated systems.
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| 44. |
- Baryshnikov, Glib V., et al.
(författare)
-
Anion-induced exchange interactions in binuclear complexes of Cu(II) with flexible hexadentate bispicolylamidrazone ligands
- 2016
-
Ingår i: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 661, s. 48-52
-
Tidskriftsartikel (refereegranskat)abstract
- Two recently synthesized copper(II) complexes with spacer-armed bispicolylamidrazone ligands have been theoretically studied at the density functional theory (DFT) level accounting for empirical dispersion correction and intrinsic anionic environment by perchlorate ions. The exchange parameter between the open-shell singlet and triplet states of the studied complexes has been estimated by broken symmetry DFT calculations. The mechanism of spin-spin exchange interaction between the unpaired electrons via the σ-bond aliphatic chain (Gusev et al., 2015) is confirmed. Instead, a anion-induced mechanism is proposed which means that the anionic grid participates in the exchange interaction between the unpaired electrons.
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| 45. |
- Baryshnikov, G. V., et al.
(författare)
-
Application of Bader's atoms in molecules theory to the description of coordination bonds in the complex compounds of Ca2+ and Mg2+ with methylidene rhodanine and its anion
- 2012
-
Ingår i: Russian journal of general chemistry. - 1070-3632 .- 1608-3350. ; 82:7, s. 1254-1262
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Tidskriftsartikel (refereegranskat)abstract
- In the framework of Bader's atoms in molecules theory a complete analysis of the distribution function of electron density in molecules of complexes of Ca2+ and Mg2+ with methylidene rhodanine and its anion was carried out. The role of mutual polarization of the metal cation and the ligand in the formation of coordination bonds was demonstrated. The accumulation of electron density in the interatomic space of coordination bonds is assumed to be a consequence of the deformation of the ligand electron shell under the influence of the cation electric field. Based on the magnitude and sign of the Laplacian and the electron energy density at the critical points of coordination bonds the interactions were classified the in terms of the atoms in molecules theory. The energy of the coordination bonds was evaluated using the Espinoza's formula. The stability of metal-containing rings was considered basing on the values of the bond ellipticity.
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| 46. |
- Baryshnikov, Gleb V., et al.
(författare)
-
Aromaticity and photophysics of tetrasila- and tetragerma-annelated tetrathienylenes as new representatives of the hetero[8]circulene family
- 2019
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 21:18, s. 9246-9254
-
Tidskriftsartikel (refereegranskat)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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| 47. |
- Baryshnikov, Glib, V., et al.
(författare)
-
Aromaticity of Even-Number Cyclo[n]carbons (n=6-100)
- 2020
-
Ingår i: Journal of Physical Chemistry A. - : AMER CHEMICAL SOC. - 1089-5639 .- 1520-5215. ; 124:51, s. 10849-10855
-
Tidskriftsartikel (refereegranskat)abstract
- The recently synthesized cyclo[18]carbon molecule has been characterized in a number of studies by calculating electronic, spectroscopic, and mechanical properties. However, cyclo[18] carbon is only one member of the class of cyclo[n]carbons-standalone carbon allotrope representatives. Many of the larger members of this class of molecules have not been thoroughly investigated. In this work, we calculate the magnetically induced current density of cyclo[n]carbons in order to elucidate how electron delocalization and aromatic properties change with the size of the molecular ring (n), where n is an even number between 6 and 100. We find that the Hiickel rules for aromaticity (4k + 2) and antiaromaticity (4k) become degenerate for large C-n rings (n > 50), which can be understood as a transition from a delocalized electronic structure to a nonaromatic structure with localized current density fluxes in the triple bonds. Actually, the calculations suggest that cyclo[n]carbons with n > 50 are nonaromatic cyclic polyalkynes. The influence of the amount of nonlocal exchange and the asymptotic behavior of the exchange-correlation potential of the employed density functionals on the strength of the magnetically induced ring current and the aromatic character of the large cyclo[n]carbons is also discussed.
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| 48. |
- Baryshnikov, Gleb V., et al.
(författare)
-
Benzoannelated aza-, oxa- and azaoxa[8]circulenes as promising blue organic emitters
- 2016
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 18:40, s. 28040-28051
-
Tidskriftsartikel (refereegranskat)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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| 49. |
- Baryshnikov, Gleb V., et al.
(författare)
-
Computational study of aromaticity, H-1 NMR spectra and intermolecular interactions of twisted thia-norhexaphyrin and its multiply annulated polypyrrolic derivatives
- 2019
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 21:45, s. 25334-25343
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Tidskriftsartikel (refereegranskat)abstract
- The recently synthesized twisted thia-norhexaphyrin and its multiply annulated polypyrrolic derivatives have been studied computationally. Gauge-including magnetically induced current calculations predict a global nonaromatic character of the initial thia-norhexaphyrin due to the highly-twisted conformation of the macrocycle. Upon the oxidation of the thia-norhexaphyrin four multiply annulated polypyrrolic aromatic macrocycles are formed for which the global aromatic character is confirmed in agreement with experimentally measured H-1 NMR spectra. The calculation of the proton chemical shifts for the studied compounds by direct comparison with the tetramethylsilane standard leads to a significant mean absolute error. At the same time a linear regression procedure for the two selected groups of protons (CH and NH protons) provides much better values of calculated chemical shifts and tight correlation with experiment. The separate consideration of NH protons is motivated by the numerous intermolecular hydrogen bonds in which the protons are involved, which induce considerable upfield shifts, leading to a significant underestimation of the corresponding chemical shifts. Such a selected correlation can be used for accurate estimation of proton chemical shifts of the related porphyrinoids. Bader's theory of Atoms in Molecules has been applied for the studied twisted thia-norhexaphyrin and its multiply annulated polypyrrolic derivatives to characterize intramolecular H-bonds and other non-covalent interactions.
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- Baryshnikov, Gleb V., et al.
(författare)
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Cyclo[18]carbon : Insight into Electronic Structure, Aromaticity, and Surface Coupling
- 2019
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Ingår i: The Journal of Physical Chemistry Letters. - : AMER CHEMICAL SOC. - 1948-7185. ; 10:21, s. 6701-6705
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Tidskriftsartikel (refereegranskat)abstract
- Cyclo[18]carbon (C-18) is studied computationally at the density functional theory (DFT) and ab initio levels to obtain insight into its electronic structure, aromaticity, and adsorption properties on a NaCl surface. DFT functionals with a small amount of Hartree-Fock exchange fail to determine the experimentally observed polyyne molecular structure, revealing a cumulene-type geometry. Exchange-correlation functionals with a large amount of Hartree-Fock exchange as well as ab initio CASSCF calculations yield the polyyne structure as the ground state and the cumulene structure as a transition state between the two inverted polyyne structures through a Kekule distortion. The polyyne and the cumulene structures are found to be doubly Huckel aromatic. The calculated adsorption energy of cyclo[18]carbon on the NaCl surface is small (37 meV/C) and almost the same for both structures, implying that the surface does not stabilize a particular geometry.
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