71 results on '"Mitric, R."'
Search Results
2. Photo-oxidation by laser pulse induced desorption of phthalocyanines
- Author
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Holz, M., Wichmann, J., Mitrić, R., Wöste, L., and Lindinger, A.
- Published
- 2014
- Full Text
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3. Ultrafast relaxation of solvated organic molecules studied by XUV time-resolved photoelectron spectroscopy
- Author
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Granados, C., primary, Titov, E., additional, Hummert, J., additional, Ikonnikov, E., additional, Haacke, S., additional, Mitric, R., additional, and Kornilov, O., additional
- Published
- 2022
- Full Text
- View/download PDF
4. Mixed boundary value problems of the fourth kind in an enhanced theory of bending of elastic plates
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Mitric, R. and Schiavone, P.
- Subjects
Integral equations -- Usage -- Methods -- Research ,Bending -- Research -- Methods -- Usage ,Boundary value problems -- Usage -- Methods -- Research ,Elasticity -- Research -- Usage -- Methods ,Mathematics ,Physics ,Usage ,Research ,Methods - Abstract
Abstract: The real boundary integral equation method is used to solve a specific type of mixed boundary value problem in an enhanced theory of bending of elastic plates with transverse [...]
- Published
- 2006
5. Integral Solution of a Problem with Non-Standard Boundary Conditions in an Enhanced Theory of Bending of Elastic Plates
- Author
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Mitric, R. and Schiavone, P.
- Published
- 2004
- Full Text
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6. Cluster properties in the regime in which each atom counts
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Bonačić-Koutecký, V., Mitrić, R., Bürgel, C., and Schäfer-Bung, B.
- Published
- 2006
- Full Text
- View/download PDF
7. Ab initio adiabatic dynamics combined with wigner distribution approach to femtosecond pump-probe negative ion to neutral to positive ion (NeNePo) spectroscopy of Ag(sub)2Au, Ag(sub)4, and Au(sub)4 clusters
- Author
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Mitric, R., Hartmann, M., Stanca, B., Bonacic-Koutecky, V., and Fantucci, P.
- Subjects
Chemistry, Physical and theoretical -- Research ,Ions -- Analysis ,Electrons -- Analysis ,Spectral energy distribution -- Analysis ,Molecular dynamics -- Research ,Chemicals, plastics and rubber industries - Published
- 2001
8. Experimental and theoretical 2p core-level spectra of size-selected gas-phase aluminum and silicon cluster cations: Chemical shifts, geometric structure, and coordination-dependent screening
- Author
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Walter, M., Vogel, M., Zamudio-Bayer, V., Lindbad, R., Reichenbach, T., Hirsch, K., Langenberg, A., Rittmann, J., Kulesza, A., Mitric, R., Moseler, M., Möller, T., Issendorff, B. von, Lau, J.T., and Publica
- Subjects
x-ray ,core-level spectroscopy ,cationic aluminum cluster ,core-level shift ,2p photoionization ,silicon cluster ,silicon surface - Abstract
We present 2p core-level spectra of size-selected aluminum and silicon cluster cations from soft X-ray photoionization efficiency curves and density functional theory. The experimental and theoretical results are in very good quantitative agreement and allow for geometric structure determination. New ground state geometries for Al12+, Si15+, Si16+, and Si19+ are proposed on this basis. The chemical shifts of the 2p electron binding energies reveal a substantial difference for aluminum and silicon clusters: while in aluminum the 2p electron binding energy decreases with increasing coordination number, no such correlation was observed for silicon. The 2p binding energy shifts in clusters of both elements differ strongly from those of the corresponding bulk matter. For aluminum clusters, the core-level shifts between outer shell atoms and the encapsulated atom are of opposite sign and one order of magnitude larger than the corresponding core-level shift between surface and bulk atoms in the solid. For silicon clusters, the core-level shifts are of the same order of magnitude in clusters and in bulk silicon but no obvious correlation of chemical shift and bond length, as present for reconstructed silicon surfaces, are observed.
- Published
- 2019
9. Vibrational spectra and DFT calculations of PPV-oligomers
- Author
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Hrenar, T, Mitrić, R, Meić, Z, Meier, H, and Stalmach, U
- Published
- 2003
- Full Text
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10. Different approaches for the calculation of electronic excited states of nonstoichiometric alkali halide clusters: The example of Na3F.
- Author
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Durand, G., Heitz, M.-C., Spiegelman, F., Meier, C., Mitric, R., Bonacáic-Koutecké, V., and Pittner, J.
- Subjects
ABSORPTION ,EUCLID'S elements ,ABSORPTION spectra ,MOLECULAR spectroscopy ,ELECTRONIC structure ,POTENTIAL energy surfaces - Abstract
The electronic structure and excited states of the Na
3 F cluster are investigated using different approximate, but numerically efficient, computational schemes, such as a 2e hybrid quantum/classical pseudopotential model with full-configuration interaction or time-dependent density-functional theory. Various quantities such as geometries and transition energies are compared with results previously obtained by multireference configuration interaction calculations, taken as reference data. The potential energy surfaces of the lowest excited states are investigated and the finite-temperature absorption spectra are calculated. The good agreement with recent beam experiments [J.-M. L’Hermite, V. Blanchet, A. Le Padellec, B. Lamory, and P. Labastie, Eur. Phys. J. D 28, 361 (2004)] leads to the conclusion that the absorption spectrum observed experimentally corresponds to the lowest energy isomer which has a C2v planar rhombic geometry. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]- Published
- 2004
- Full Text
- View/download PDF
11. Ultrafast excited state dynamics of the Na3F cluster: Quantum wave packet and classical trajectory calculations compared to experimental results.
- Author
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Heitz, M.-C., Durand, G., Spiegelman, F., Meier, C., Mitric, R., and Bonacic-Kouteckä, V.
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WAVE packets ,FLUCTUATIONS (Physics) ,QUANTUM theory ,STATICS ,VIBRATIONAL spectra ,PHYSICS - Abstract
Short-time, excited-state dynamics of the lowest isomer of the Na
3 F cluster is studied theoretically in order to interpret the features of recent time-resolved pump-probe ionization experiments [J. M. L’Hermite, V. Blanchet, A. Le Padellec, B. Lamory, and P. Labastie, Eur. Phys. J. D 28, 361 (2004)]. In the present paper, we propose an identification of the vibrational motion responsible for the oscillations in the ion signal, on the basis of quantum mechanical wave packet propagations and classical trajectory calculations. The good agreement between experiment and theory allows for a clear interpretation of the detected dynamics. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]- Published
- 2004
- Full Text
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12. A DFT study of EPR parameters in Cu(II) complexes of the octarepeat region of the prion protein
- Author
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Bruschi, M, DE GIOIA, L, Mitric, R, Bonacic Koutecký, V, Fantucci, P, BRUSCHI, MAURIZIO, DE GIOIA, LUCA, FANTUCCI, PIERCARLO, Mitric R, Bonacic Koutecký V, Bruschi, M, DE GIOIA, L, Mitric, R, Bonacic Koutecký, V, Fantucci, P, BRUSCHI, MAURIZIO, DE GIOIA, LUCA, FANTUCCI, PIERCARLO, Mitric R, and Bonacic Koutecký V
- Abstract
The present paper shows how theoretically determined electron paramagnetic resonance (EPR) parameters can help in assigning the most favorable structure of Cu(II) complexes in octarepeat (OR) regions (PHGGGWGQ) of the prion protein (PrP). This could contribute to a better understanding of the molecular structure of the Cu(OR) complexes, as some features of such species in solution are still unclear. The present theoretical investigation on [Cu(II)(HGGG)] and [Cu(II)(HGGGW)] complexes was carried out to confirm the stability of relevant isomers, and in particular, to evaluate the hyperfine coupling constants (hcc) with 63Cu, 14N and 17O nuclei, as well as the g values. The hcc (and to a lesser extent the g components) are useful probes for checking whether the computed EPR parameters for specific isomers fit the experimental data, thus permitting the association of the observed spectra with a specific complex structure. The results obtained suggest that the Cu(II) ion in the [Cu(HGGG)] isomers prefers a square pyramidal coordination with three nitrogen atoms of the peptide and one carbonyl oxygen atom in the basal plane. Also the Cu(II) ion in the [Cu(HGGGW)] complex is penta-coordinated. The penta-coordination does not actually involve the tryptophan residue but an additional water molecule, forced to occupy the axial coordination position by a rather extended hydrogen-bond network, promoted by the tryptophan residue.The comparison between the calculated and experimental values of EPR parameters allows one to suggest the assignment of the coordination mode of the Cu(II) ion in the considered peptide ligands. The computed values of the g components seem to be little affected by a particular coordination mode. In particular, the g component is always underestimated by about 0.1 with respect to the experiment. The calculated values of the hcc, in contrast, are in acceptable agreement with the experimental values, in spite of the fact that the large size of the species
- Published
- 2008
13. Nonadiabatic dynamics within time-dependent density functional tight binding method.
- Author
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Mitric, R., Werner, U., Wohlgemuth, M., Seifert, G., Bonacic-Koutecky, V., Mitric, R., Werner, U., Wohlgemuth, M., Seifert, G., and Bonacic-Koutecky, V.
- Abstract
Contains fulltext : 81293.pdf (publisher's version ) (Closed access), A nonadiabatic molecular dynamics is implemented in the framework of the time-dependent density functional tight binding method (TDDFTB) combined with Tully's stochastic surface hopping algorithm. The applicability of our method to complex molecular systems is illustrated on the example of the ultrafast excited state dynamics of microsolvated adenine. Our results demonstrate that in the presence of water, upon initial excitation to the S(3) (pi-pi*) state at 260 nm, an ultrafast relaxation to the S(1) state with a time constant of 16 fs is induced, followed by the radiationless decay to the ground state with a time constant of 200 fs.
- Published
- 2009
14. Optical and Structural Properties of Copper−Oxytocin Dications in the Gas Phase
- Author
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Joly, L, Antoine, R, Albrieux, F, Ballivian, R, Broyer, M, Chirot, F, Lemoine, J, Dugourd, P, Greco, C, Mitric, R, Bonacic Koutecky, V, Bonacic Koutecky, V., GRECO, CLAUDIO, Joly, L, Antoine, R, Albrieux, F, Ballivian, R, Broyer, M, Chirot, F, Lemoine, J, Dugourd, P, Greco, C, Mitric, R, Bonacic Koutecky, V, Bonacic Koutecky, V., and GRECO, CLAUDIO
- Abstract
We present a joint experimental and theoretical investigation of the structural and optical properties of copper-oxytocin dications in the gas phase. Ion mobility and UV photodissociation experiments were performed, allowing the investigation of the influence of the Cu2+ ion on the structural and optical properties of oxytocin. Density functional theory calculations were performed to find low energy structures for the bare and complexed peptide and to characterize optical spectral features. Copper complexation induces a drastic change in the structure of the oxytocin peptide. In particular, we predict a 4N chelation of the copper cation which leads to a contraction of the oxytocin ring. The gas phase lowest-energy structures are compared with the X-ray crystal structure of the oxytocin molecule bound to its receptor protein. The optical spectrum of oxytocin complexed with the copper cation displays a global enhancement of the photofragmentation yield as compared to the one recorded for the doubly protonated oxytocin. Moreover, experimental and calculated optical spectra of protonated tyrosine have also been determined, since its leading features are present in oxytocin as well. © 2009 American Chemical Society.
- Published
- 2009
15. The structures of vanadium oxide cluster-ethene complexes. A combined ir multiple photon dissociation spectroscopy and dft calculation study
- Author
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Fielicke, A., Mitric, R., Meijer, G.J.M., Bonacic-Koutecky, V., Helden, G.J. von, Fielicke, A., Mitric, R., Meijer, G.J.M., Bonacic-Koutecky, V., and Helden, G.J. von
- Abstract
Contains fulltext : 98919.pdf (publisher's version ) (Open Access)
- Published
- 2003
16. Density functional study of structural and electronic properties of bimetallic silver-gold clusters: Comparison with pure gold and silver clusters
- Author
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Bonacic Koutecky, V, Burda, J, Mitric, R, Ge, M, Zampella, G, Fantucci, P, Ge, MF, ZAMPELLA, GIUSEPPE, FANTUCCI, PIERCARLO, Bonacic Koutecky, V, Burda, J, Mitric, R, Ge, M, Zampella, G, Fantucci, P, Ge, MF, ZAMPELLA, GIUSEPPE, and FANTUCCI, PIERCARLO
- Abstract
Bimetallic silver-gold clusters offer an excellent opportunity to study changes in metallic versus "ionic" properties involving charge transfer as a function of the size and the composition, particularly when compared to pure silver and gold clusters. We have determined structures, ionization potentials, and vertical detachment energies for neutral and charged bimetallic AgmAun [3less than or equal to(m+n)less than or equal to5] clusters. Calculated VDE values compare well with available experimental data. In the stable structures of these clusters Au atoms assume positions which favor the charge transfer from Ag atoms. Heteronuclear bonding is usually preferred to homonuclear bonding in clusters with equal numbers of hetero atoms. In fact, stable structures of neutral Ag2Au2, Ag3Au3, and Ag4Au4 clusters are characterized by the maximum number of hetero bonds and peripheral positions of Au atoms. Bimetallic tetramer as well as hexamer are planar and have common structural properties with corresponding one-component systems, while Ag4Au4 and Ag-8 have 3D forms in contrast to Au-8 which assumes planar structure. At the density functional level of theory we have shown that this is due to participation of d electrons in bonding of pure Au-n clusters while s electrons dominate bonding in pure Ag-m as well as in bimetallic clusters. In fact, Au-n clusters remain planar for larger sizes than Ag-m and AgnAun clusters. Segregation between two components in bimetallic systems is not favorable, as shown in the example of Ag5Au5 cluster. We have found that the structures of bimetallic clusters with 20 atoms Ag10Au10 and Ag12Au8 are characterized by negatively charged Au subunits embedded in Ag environment. In the latter case, the shape of Au-8 is related to a pentagonal bipyramid capped by one atom and contains three exposed negatively charged Au atoms. They might be suitable for activating reactions relevant to catalysis. According to our findings the charge transfer in bimeta
- Published
- 2002
17. Boundary Integral Equation Methods for a Refined Model of Elastic Plates
- Author
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Mitric, R., primary and Constanda, C., additional
- Published
- 2006
- Full Text
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18. Mixed Boundary Value Problems of the Fourth Kind in an Enhanced Theory of Bending of Elastic Plates
- Author
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Mitric, R., primary and Schiavone, P., additional
- Published
- 2005
- Full Text
- View/download PDF
19. Structural properties and reactivity of bimetallic silver-gold clusters
- Author
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Mitric, R., primary, B�rgel, C., additional, Burda, J., additional, Bonacic-Kouteck�, V., additional, and Fantucci, P., additional
- Published
- 2003
- Full Text
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20. New strategy for optimal control of femtosecond pump-dump processes applicable to systems of moderate complexity
- Author
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Mitric, R., primary, Hartmann, M., additional, Pittner, J., additional, and Bonacic-Kouteck�, V., additional
- Published
- 2003
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- View/download PDF
21. $$ {\rm{V}}_2 {\rm{O}}_5^ + $$ reaction with C 2 H 4 : theoretical considerations of experimental findings
- Author
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Justes, D. R., primary, Castleman, A. W., additional, Mitric, R., additional, and Bonacic-Kouteck�, V., additional
- Published
- 2003
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22. Kinetics and equilibrium of small metallic clusters: Ab initio confinement molecular dynamics study of 4
- Author
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Chekmarev, S. F., primary, Mitric, R., additional, and Bonacic-Kouteck�, V., additional
- Published
- 2003
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23. Integral methods for mechanical sensor design and performance testing in plates with transverse shear deformation and transverse normal strain.
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Mitric, R. and Schiavone, P.
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- 2005
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24. Optimal Control of Ionization Processes in NaK: Comparison between Theory and Experiment.
- Author
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Schafer-Bung, B., Mitric, R., Bonacic-Koutecky, V., Lindinger, A., Lupulescu, C., Vajda, S., Weber, S. M., and Woste, L.
- Subjects
- *
ELECTRONIC systems , *CYBERNETICS , *PROCESS control systems , *SYSTEM analysis - Abstract
We report a good agreement between the shapes of tailored pulses obtained theoretically and experimentally by using the optimal-control theory and the closed-loop learning technique to maximize the ionization yield in NaK. The theoretical pulse shapes are found to be robust regarding the choice of the initial guess. We assign the leading features of the pulse shapes to processes underlying the optimal control and reveal the mechanism which involves an electronic transition followed by a direct two-photon process and sequential one-photon processes at later times. We show that the optimal control not only serves for maximizing the desired yield but also as a tool for the analysis and the identification of the responsible processes. [ABSTRACT FROM AUTHOR]
- Published
- 2004
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- View/download PDF
25. Photostabilization of the ultracold Rb2molecule by optimal control
- Author
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Schäfer-Bung, B, Mitric, R, and Bonacic-Koutecký, V
- Abstract
We present a theoretical study of the photostabilization of the ultracold Rb2molecule by tailored laser fields. The simulations involve the ground and two excited electronic states, taking into account spin-orbit coupling, and are based on the full quantum mechanical optimal control theory. We demonstrate starting from a highly excited bound vibrational state that almost 100% population of the ground state v= 0 vibrational level can be achieved. The obtained optimal pulse has a long temporal and very broad spectral range. Our results reveal the mechanism of the photostabilization process and allow the proposal of new strategies for the formation of ultracold molecules taking into account the necessary constraints for possible experimental realization.
- Published
- 2006
- Full Text
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26. New Strategy for Optimal Control of Femtosecond Pump−Dump Processes
- Author
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Mitric, R., Hartmann, M., Pittner, J., and Bonacic-Koutecky, V.
- Abstract
We propose a new strategy for optimal control with tailored pump−dump pulses which drive a system of moderate complexity via electronically excited states to a desired objective in the ground state with a maximal yield. It is based on the concept of the intermediate target in the excited state which selects the appropriate Franck−Condon window at a given time delay between the two pulses mandatory for reaching optimally the objective. The existence of the intermediate target ensures the connective pathway between the initial state and the objective in the ground state, necessary for the controllability of multidimensional systems involving two electronic states. We show the scope of this concept by optimizing and analyzing the pump and dump pulses for driving the isomerization process in the Na
3 F2 cluster to the second isomer by suppressing radiationless transition through the conical intersection between the first excited and the ground state. This has been realized by employing our ab initio Wigner distribution approach.- Published
- 2002
- Full Text
- View/download PDF
27. Ab Initio Adiabatic Dynamics Combined with Wigner Distribution Approach to Femtosecond Pump−Probe Negative Ion to Neutral to Positive Ion (NeNePo) Spectroscopy of Ag<INF>2</INF>Au, Ag<INF>4</INF>, and Au<INF>4</INF> Clusters
- Author
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Mitric, R., Hartmann, M., Stanca, B., Bonacic-Koutecky, V., and Fantucci, P.
- Abstract
Ultrafast ground state nuclear dynamics of small coinage metal clusters is theoretically explored in the framework of negative ion to neutral to positive ion (NeNePo) femtosecond pump−probe spectroscopy with the aim to determine the scope and perspective of this technique. This approach involves the preparation of an initial ensemble in the anionic ground state of the cluster, one-photon detachment by the pump pulse, the propagation of the system on the neutral electronic ground state, and detection via the cationic ground state by a time-delayed ionizing probe pulse. The calculations of the NeNePo-ZEKE signals under the condition of zero kinetic energy electrons are based on the combination of the Wigner distribution approach and ab initio molecular dynamics (MD) on the fly in the framework of gradient-corrected DFT for the propagation of an ensemble of classical trajectories and involves the average over the entire phase space. We have chosen examples of Ag
2 Au and Au4 to investigate time scales and the character of isomerization processes that are influenced by a local minimum corresponding to an energetically high-lying isomer with the structure related to the initial anionic structure. Capture of the nuclei within the local minimum takes place with dephased (Ag2 Au) or nondephased (Au4 ) vibrational relaxation. Structural relaxations leading to isomerization processes are in both cases of delocalized nature and take place after 1 ps. In contrast, the Ag4 cluster represents an example for which isomerization processes do not occur, since rhombic structures with slightly different bond lengths are global minima of the anionic and neutral ground states. Therefore, the relaxation dynamics is characterized by regular oscillations, which serve as fingerprints of structural properties. On the basis of the analysis of pump−probe signals and underlying dynamics, this contribution provides information about conditions under which structural properties of gas-phase clusters (global and local minima) and isomerization processes can be observed in the framework of the NeNePo-ZEKE type of spectroscopy. The latter is important in the context of applicability of this technique to the investigation of cluster reactivity.- Published
- 2001
28. 2p core-level binding energies of size-selected free silicon clusters: Chemical shifts and cluster structure.
- Author
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Vogel, M., Kasigkeit, C., Hirsch, K., Langenberg, A., Rittmann, J., Zamudio-Bayer, V., Kulesza, A., Mitric, R., Möller, T., Issendorff, B. v., and Lau, J. T.
- Subjects
- *
BINDING energy , *SILICON , *CHEMICAL shift (Nuclear magnetic resonance) , *X-rays , *PHOTOIONIZATION , *ELECTRON distribution - Abstract
The 2p core-level electron binding energies of size-selected silicon cluster ions have been determined from soft x-ray photoionization efficiency curves. Local chemical shifts and global charging energy contributions to the 2p binding energy can be separated, because core-level and valence-band electron binding energies exhibit the same inverse radius dependence. The experimental 2p binding energy distributions show characteristic size-specific patterns that are well reproduced by the corresponding electronic density of states obtained from density functional theory modeling. These results demonstrate that 2p binding energies in silicon clusters are dominated by initial state effects, i.e., by the interaction with the local valence electron density, and can thus be used to corroborate structural assignments. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
29. Optical and Structural Properties of Copper−Oxytocin Dications in the Gas Phase
- Author
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Jérôme Lemoine, Renaud Ballivian, Florian Albrieux, Laure Joly, Michel Broyer, Roland Mitrić, Vlasta Bonačić-Koutecký, Rodolphe Antoine, Philippe Dugourd, Fabien Chirot, Claudio Greco, Joly, L, Antoine, R, Albrieux, F, Ballivian, R, Broyer, M, Chirot, F, Lemoine, J, Dugourd, P, Greco, C, Mitric, R, and Bonacic Koutecky, V
- Subjects
Molecular Structure ,Cations, Divalent ,Photodissociation ,Analytical chemistry ,chemistry.chemical_element ,Time-dependent density functional theory ,Crystallography, X-Ray ,Oxytocin ,Copper ,Surfaces, Coatings and Films ,Gas phase ,Ion ,Oxytocin, TDDFT ,chemistry ,Materials Chemistry ,Physical chemistry ,Gases ,Physical and Theoretical Chemistry - Abstract
We present a joint experimental and theoretical investigation of the structural and optical properties of copper-oxytocin dications in the gas phase. Ion mobility and UV photodissociation experiments were performed, allowing the investigation of the influence of the Cu2+ ion on the structural and optical properties of oxytocin. Density functional theory calculations were performed to find low energy structures for the bare and complexed peptide and to characterize optical spectral features. Copper complexation induces a drastic change in the structure of the oxytocin peptide. In particular, we predict a 4N chelation of the copper cation which leads to a contraction of the oxytocin ring. The gas phase lowest-energy structures are compared with the X-ray crystal structure of the oxytocin molecule bound to its receptor protein. The optical spectrum of oxytocin complexed with the copper cation displays a global enhancement of the photofragmentation yield as compared to the one recorded for the doubly protonated oxytocin. Moreover, experimental and calculated optical spectra of protonated tyrosine have also been determined, since its leading features are present in oxytocin as well. © 2009 American Chemical Society.
- Published
- 2009
30. Density functional study of structural and electronic properties of bimetallic silver–gold clusters: Comparison with pure gold and silver clusters
- Author
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Maofa Ge, Jaroslav V. Burda, Vlasta Bonačić-Koutecký, Roland Mitrić, Giuseppe Zampella, Piercarlo Fantucci, Bonacic Koutecky, V, Burda, J, Mitric, R, Ge, M, Zampella, G, and Fantucci, P
- Subjects
CHIM/03 - CHIMICA GENERALE E INORGANICA ,Chemistry ,General Physics and Astronomy ,Ionic bonding ,Electronic structure ,Homonuclear molecule ,Crystallography ,Heteronuclear molecule ,Chemical bond ,DFT, gold, silver, metal cluster, chemical bond, quantum mechanics ,Physics::Atomic and Molecular Clusters ,Molecule ,Density functional theory ,Physical and Theoretical Chemistry ,Atomic physics ,Bimetallic strip - Abstract
Bimetallic silver-gold clusters offer an excellent opportunity to study changes in metallic versus "ionic" properties involving charge transfer as a function of the size and the composition, particularly when compared to pure silver and gold clusters. We have determined structures, ionization potentials, and vertical detachment energies for neutral and charged bimetallic AgmAun [3less than or equal to(m+n)less than or equal to5] clusters. Calculated VDE values compare well with available experimental data. In the stable structures of these clusters Au atoms assume positions which favor the charge transfer from Ag atoms. Heteronuclear bonding is usually preferred to homonuclear bonding in clusters with equal numbers of hetero atoms. In fact, stable structures of neutral Ag2Au2, Ag3Au3, and Ag4Au4 clusters are characterized by the maximum number of hetero bonds and peripheral positions of Au atoms. Bimetallic tetramer as well as hexamer are planar and have common structural properties with corresponding one-component systems, while Ag4Au4 and Ag-8 have 3D forms in contrast to Au-8 which assumes planar structure. At the density functional level of theory we have shown that this is due to participation of d electrons in bonding of pure Au-n clusters while s electrons dominate bonding in pure Ag-m as well as in bimetallic clusters. In fact, Au-n clusters remain planar for larger sizes than Ag-m and AgnAun clusters. Segregation between two components in bimetallic systems is not favorable, as shown in the example of Ag5Au5 cluster. We have found that the structures of bimetallic clusters with 20 atoms Ag10Au10 and Ag12Au8 are characterized by negatively charged Au subunits embedded in Ag environment. In the latter case, the shape of Au-8 is related to a pentagonal bipyramid capped by one atom and contains three exposed negatively charged Au atoms. They might be suitable for activating reactions relevant to catalysis. According to our findings the charge transfer in bimetallic clusters is responsible for formation of negatively charged gold subunits which are expected to be reactive, a situation similar to that of gold clusters supported on metal oxides. (C) 2002 American Institute of Physics.
- Published
- 2002
31. BLUF Hydrogen network dynamics and UV/Vis spectra: A combined molecular dynamics and quantum chemical study
- Author
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Jan P. Götze, Roland Mitrić, Peter Saalfrank, Claudio Greco, Vlasta Bonačić-Koutecký, Gotze, J, Greco, C, Mitric, R, Bonacic Koutecky, V, and Saalfrank, P
- Subjects
Time Factors ,Flavoproteins ,Hydrogen bond ,Chemistry ,Protonation ,Hydrogen Bonding ,General Chemistry ,Flavin group ,Rhodobacter sphaeroides ,Chromophore ,Photochemistry ,Photochemical Processes ,Spectral line ,Photoexcitation ,Molecular Docking Simulation ,Computational Mathematics ,Molecular dynamics ,Chemical physics ,Flavins ,Quantum Theory ,Density functional theory ,Spectrophotometry, Ultraviolet ,BLUF, Molecular Dynamics - Abstract
Blue light sensing using flavin (BLUF) protein photoreceptor domains change their hydrogen bond network after photoexcitation. To explore this phenomenon, BLUF domains from R. sphaeroides were simulated using Amber99 molecular dynamics (MD). Five starting configurations were considered, to study different BLUF proteins (AppA/BlrB), Trp conformations ("Win"/"W out"), structure determination (X-ray/NMR), and finally, His protonation states. We found dependencies of the hydrogen bonds on almost all parameters. Our data show an especially strong correlation of the Trp position and hydrogen bonds involving Gln63. The latter is in some contradiction to earlier results (Obanayama et al., Photochem. Photobiol. 2008, 84 10031010). Possible origins and implications are discussed. Our calculations support conjectures that Gln63 is more flexible with Trp104 in Win position. Using snapshots from MD and time-dependent density functional theory, UV/vis spectra for the chromophore were determined, which account for molecular motion of the protein under ambient conditions. In accord with experiment, it is found that the UV/vis spectra of BLUF bound flavin are red-shifted and thermally broadened for all calculated π → π* transitions, relative to gas phase flavin at T = 0 K. However, differences in the spectra between the various BLUF configurations cannot be resolved with the present approach. © 2012 Wiley Periodicals, Inc.
- Published
- 2012
32. A DFT study of EPR parameters in Cu(II) complexes of the octarepeat region of the prion protein
- Author
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Piercarlo Fantucci, Vlasta Bonačić-Koutecký, Maurizio Bruschi, Luca De Gioia, Roland Mitrić, Bruschi, M, DE GIOIA, L, Mitric, R, Bonacic Koutecký, V, and Fantucci, P
- Subjects
Models, Molecular ,Repetitive Sequences, Amino Acid ,Hyperfine Coupling Constant ,Prions ,Chemistry ,Stereochemistry ,Hydrogen bond ,Electron Spin Resonance Spectroscopy ,General Physics and Astronomy ,Cu-complexe ,Square pyramidal molecular geometry ,Spectral line ,Ion ,law.invention ,Crystallography ,Ab initio quantum chemistry methods ,law ,Prion ,Molecule ,Density functional theory ,EPR ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Copper ,Density Functional Theory - Abstract
The present paper shows how theoretically determined electron paramagnetic resonance (EPR) parameters can help in assigning the most favorable structure of Cu(ii) complexes in octarepeat (OR) regions (PHGGGWGQ) of the prion protein (PrP). This could contribute to a better understanding of the molecular structure of the Cu(OR) complexes, as some features of such species in solution are still unclear. The present theoretical investigation on [Cu(ii)(HGGG)] and [Cu(ii)(HGGGW)] complexes was carried out to confirm the stability of relevant isomers, and in particular, to evaluate the hyperfine coupling constants (hcc) with (63)Cu, (14)N and (17)O nuclei, as well as the g values. The hcc (and to a lesser extent the g components) are useful probes for checking whether the computed EPR parameters for specific isomers fit the experimental data, thus permitting the association of the observed spectra with a specific complex structure. The results obtained suggest that the Cu(ii) ion in the [Cu(HGGG)] isomers prefers a square pyramidal coordination with three nitrogen atoms of the peptide and one carbonyl oxygen atom in the basal plane. Also the Cu(ii) ion in the [Cu(HGGGW)] complex is penta-coordinated. The penta-coordination does not actually involve the tryptophan residue but an additional water molecule, forced to occupy the axial coordination position by a rather extended hydrogen-bond network, promoted by the tryptophan residue. The comparison between the calculated and experimental values of EPR parameters allows one to suggest the assignment of the coordination mode of the Cu(ii) ion in the considered peptide ligands. The computed values of the g components seem to be little affected by a particular coordination mode. In particular, the g( parallel) component is always underestimated by about 0.1 with respect to the experiment. The calculated values of the hcc, in contrast, are in acceptable agreement with the experimental values, in spite of the fact that the large size of the species under consideration forced us to accept a certain level of approximation in the computational procedure. Nevertheless, the present study must be considered as one of the first examples of truly ab initio calculations of EPR parameters for systems as large as the Cu(OR)-type complexes.
- Published
- 2008
33. Full Electron Delocalization across the Cluster in 1,12-bisBMes 2 - p -carborane Radical Anion.
- Author
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Wu L, Zhang X, Moos M, Krummenacher I, Dietz M, Jayaraman A, Bertermann R, Ye Q, Finze M, Wenzel M, Mitric R, Lambert C, Braunschweig H, and Ji L
- Abstract
Conjugation between three-dimensional (3D) carboranes and the attached substituents is commonly believed to be very weak. In this paper, we report that reducing 1,12-bis(BMes
2 )- p -carborane ( B2 p Cab ) with one electron gives a radical anion with a centrosymmetric semiquinoidal structure. This radical anion shows extensive electron delocalization between the two boron centers over the p -carborane bridge due to the overlap of carborane lowest unoccupied molecular orbital (LUMO) and the BMes2 LUMO. Unlike dianions of other C2 B10 H12 carboranes, which rearrange to a nido -form, two-electron reduction of B2 p Cab leads to a rearrangement into a basket-shaped intermediate.- Published
- 2024
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34. Onset of spin entanglement in doped carbon nanotubes studied by EPR.
- Author
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Sperlich A, Eckstein KH, Oberndorfer F, Sturdza BK, Auth M, Dyakonov V, Mitric R, and Hertel T
- Abstract
Nanoscale semiconductors with isolated spin impurities have been touted as promising materials for their potential use at the intersection of quantum, spin, and information technologies. Electron paramagnetic resonance (EPR) studies of spins in semiconducting carbon nanotubes have overwhelmingly focused on spins more strongly localized by sp3-type lattice defects. However, the creation of such impurities is irreversible and requires specific reactions to generate them. Shallow charge impurities, on the other hand, are more readily and widely produced by simple redox chemistry, but have not yet been investigated for their spin properties. Here, we use EPR to study p-doped (6,5) semiconducting single-wall carbon nanotubes (s-SWNTs) and elucidate the role of impurity-impurity interactions in conjunction with exchange and correlation effects for the spin behavior of this material. A quantitative comparison of the EPR signals with phenomenological modeling combined with configuration interaction electronic structure calculations of impurity pairs shows that orbital overlap, combined with exchange and correlation effects, causes the EPR signal to disappear due to spin entanglement for doping levels corresponding to impurity spacings of 14 nm (at 30 K). This transition is predicted to shift to higher doping levels with increasing temperature and to lower levels with increasing screening, providing an opportunity for improved spin control in doped s-SWNTs., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)
- Published
- 2024
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35. Prediction of fluorescence quantum yields using the extended thawed Gaussian approximation.
- Author
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Wenzel M and Mitric R
- Abstract
Spontaneous emission and internal conversion rates are calculated within harmonic approximations and compared to the results obtained within the semi-classical extended thawed Gaussian approximation (ETGA). This is the first application of the ETGA in the calculation of internal conversion and emission rates for real molecular systems, namely, formaldehyde, fluorobenzene, azulene, and a dicyano-squaraine dye. The viability of the models as black-box tools for prediction of spontaneous emission and internal conversion rates is assessed. All calculations were done using a consistent protocol in order to investigate how different methods perform without previous experimental knowledge using density functional theory (DFT) and time-dependent DFT (TD-DFT) with B3LYP, PBE0, ωB97XD, and CAM-B3LYP functionals. Contrasting the results with experimental data shows that there are further improvements required before theoretical predictions of emission and internal conversion rates can be used as reliable indicators for the photo-luminescence properties of molecules. We find that the ETGA performs rather similar to the vertical harmonical model. Including anharmonicities in the calculation of internal conversion rates has a moderate effect on the quantitative results in the studied systems. The emission rates are fairly stable with respect to computational parameters, but the internal conversion rate reveals itself to be highly dependent on the choice of the spectral line shape function, particularly the width of the Lorentzian function, associated with homogeneous broadening., (© 2023 Author(s). Published under an exclusive license by AIP Publishing.)
- Published
- 2023
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36. Chiroptical Properties of Planar Benzobisthiazole-Bridged Squaraine Dimers.
- Author
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Freytag E, Kreimendahl L, Holzapfel M, Petersen J, Lackinger H, Stolte M, Würthner F, Mitric R, and Lambert C
- Abstract
Five chiral squaraine dimers were synthesized by fusing chiral indolenine semisquaraines with three different benzobisthiazole bridges. The thereby created squaraine dimers show a strong splitting of the lowest energy absorption bands caused by exciton coupling. The intensities of the two exciton transitions and the energetic splitting depend on the angle of the two squaraine moieties within the chromophore dimer. The electric circular dichroism spectra of the dimers show intense Cotton effects whose sign depends on the used squaraine chromophores. Sizable anisotropies g
abs of up to 2.6 × 10-3 could be obtained. TD-DFT calculations were used to partition the rotational strength into the three Rosenfeld terms where the electric-magnetic coupling turned out to be the dominant contribution while the exciton chirality term is much smaller. This is because the chromophore dimers are essentially planar but the angle between the electric transition dipole moment of one squaraine and the magnetic transition dipole moment of the other squaraine strongly deviates from 90°, which makes the dot product between the two moment vectors and, thus, the rotational strength substantial.- Published
- 2023
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37. Ultrafast Ring Closure Reaction of Gaseous cis -Stilbene from S 1 (ππ*).
- Author
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Karashima S, Miao X, Kanayama A, Yamamoto YI, Nishitani J, Kavka N, Mitric R, and Suzuki T
- Abstract
cis -Stilbene ( cis -St) is a well-known benchmark system for cis - trans photoisomerization. cis -St also produces 4a,4b-dihydrophenanthrene (DHP) in solution with a quantum yield of less than 0.19. The ring closure reaction, however, has never been identified for gaseous cis -St, and a recent computational simulation predicted the quantum yield of DHP to be only 0.04. In the present study, we identified an ultrafast ring closure reaction of gaseous cis -St for the first time using extreme ultraviolet time-resolved photoelectron spectroscopy. Surface hopping trajectory calculations at the SA3-XMS-CASPT2(2,2) level of theory reproduce the features of the observed time-resolved photoelectron spectra and predict the cis -St:DHP: trans -St branching ratio to be 0.55:0.41:0.04, in contrast with previous estimates. The results indicate that photoexcited cis -St favors ring closure over cis - trans isomerization under the isolated condition.
- Published
- 2023
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38. Internal conversion rates from the extended thawed Gaussian approximation: Theory and validation.
- Author
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Wenzel M and Mitric R
- Subjects
- Vibration, Quantum Theory
- Abstract
The theoretical prediction of the rates of nonradiative processes in molecules is fundamental in assessing their emissive properties. In this context, global harmonic models have been widely used to simulate vibronic spectra as well as internal conversion rates and to predict photoluminescence quantum yields. However, these simplified models suffer from the limitations that are inherent to the harmonic approximation and can have a severe effect on the calculated internal conversion rates. Therefore, the development of more accurate semiclassical methods is highly desirable. Here, we introduce a procedure for the calculation of nonradiative rates in the framework of the time-dependent semi-classical Extended Thawed Gaussian Approximation (ETGA). We systematically investigate the performance of the ETGA method by comparing it to the adiabatic and vertical harmonic methods, which belong to the class of widely used global harmonic models. Its performance is tested in potentials that cannot be treated adequately by global harmonic models, beginning with Morse potentials of varying anharmonicity followed by a double well potential. The calculated radiative and nonradiative internal conversion rates are compared to reference values based on exact quantum dynamics. We find that the ETGA has the capability to predict internal conversion rates in anharmonic systems with an appreciable energy gap, whereas the global harmonic models prove to be insufficient.
- Published
- 2023
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39. Stacking Is Favored over Hydrogen Bonding in Azaphenanthrene Dimers.
- Author
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Miao X, Preitschopf T, Sturm F, Fischer I, Lemmens AK, Limbacher M, and Mitric R
- Abstract
N-Doped polycyclic aromatic hydrocarbons have recently emerged as potential organic electronic materials. The function of such materials is determined not only by the intrinsic electronic properties of individual molecules but also by their supramolecular interactions in the solid state. Therefore, a proper characterization of the interactions between the individual units is of interest to materials science since they ultimately govern properties such as excitons and charge transfer. Here, we report a joint experimental and computational study of two azaphenanthrene dimers to determine the structure and the nature of supramolecular interactions in the aggregates. IR/UV double-resonance experiments were carried out using far- and mid-infrared free-electron laser radiation. The experimental spectra are compared with quantum chemical calculations for the lowest-energy π-stacked and hydrogen-bonded structures. The data reveal a preference of the π-stacked structure for the benzo[f]quinoline and the phenanthridine dimer.
- Published
- 2022
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40. Transforming Dyes into Fluorophores: Exciton-Induced Emission with Chain-like Oligo-BODIPY Superstructures.
- Author
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Patalag LJ, Hoche J, Mitric R, Werz DB, and Feringa BL
- Abstract
Herein we present a systematic study demonstrating to which extent exciton formation can amplify fluorescence based on a series of ethylene-bridged oligo-BODIPYs. A set of non- and weakly fluorescent BODIPY motifs was selected and transformed into discrete, chain-like oligomers by linkage via a flexible ethylene tether. The prepared superstructures constitute excitonically active entities with non-conjugated, Coulomb-coupled oscillators. The non-radiative deactivation channels of Internal Conversion (IC), also combined with an upstream reductive Photoelectron Transfer (rPET) and Intersystem Crossing (ISC) were addressed at the monomeric state and the evolution of fluorescence and (non-)radiative decay rates studied along the oligomeric series. We demonstrate that a "masked" fluorescence can be fully reactivated irrespective of the imposed conformational rigidity. This work challenges the paradigm that a collective fluorescence enhancement is limited to sterically induced motional restrictions., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)
- Published
- 2022
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41. Excimer formation dynamics in the isolated tetracene dimer.
- Author
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Hoche J, Flock M, Miao X, Philipp LN, Wenzel M, Fischer I, and Mitric R
- Abstract
The understanding of excimer formation and its interplay with the singlet-correlated triplet pair state
1 (TT) is of high significance for the development of efficient organic electronics. Here, we study the photoinduced dynamics of the tetracene dimer in the gas phase by time-resolved photoionisation and photoion imaging experiments as well as nonadiabatic dynamics simulations in order to obtain mechanistic insight into the excimer formation dynamics. The experiments are performed using a picosecond laser system for excitation into the S2 state and reveal a biexponential time dependence. The time constants, obtained as a function of excess energy, lie in the range between ≈10 ps and 100 ps and are assigned to the relaxation of the excimer on the S1 surface and to its deactivation to the ground state. Simulations of the quantum-classical photodynamics are carried out in the frame of the semi-empirical CISD and TD-lc-DFTB methods. Both theoretical approaches reveal a dominating relaxation pathway that is characterised by the formation of a perfectly stacked excimer. TD-lc-DFTB simulations have also uncovered a second relaxation channel into a less stable dimer conformation in the S1 state. Both methods have consistently shown that the electronic and geometric relaxation to the excimer state is completed in less than 10 ps. The inclusion of doubly excited states in the CISD dynamics and their diabatisation further allowed to observe a transient population of the1 (TT) state, which, however, gets depopulated on a timescale of 8 ps, leading finally to the trapping in the excimer minimum., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)- Published
- 2021
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42. Solvent Induced Helix Folding of Defined Indolenine Squaraine Oligomers.
- Author
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Turkin A, Holzapfel M, Agarwal M, Fischermeier D, Mitric R, Schweins R, Gröhn F, and Lambert C
- Abstract
A protecting group strategy was employed to synthesise a series of indolenine squaraine dye oligomers up to the nonamer. The longer oligomers show a distinct solvent dependence of the absorption spectra, that is, either a strong blue shift or a strong red shift of the lowest energy bands in the near infrared spectral region. This behaviour is explained by exciton coupling theory as being due to H- or J-type coupling of transition moments. The H-type coupling is a consequence of a helix folding in solvents with a small Hansen dispersity index. DOSY NMR, small angle neutron scattering (SANS), quantum chemical and force field calculations agree upon a helix structure with an unusually large pitch and open voids that are filled with solvent molecules, thereby forming a kind of clathrate. The thermodynamic parameters of the folding process were determined by temperature dependent optical absorption spectra., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)
- Published
- 2021
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43. Ultrafast Resonance Energy Transfer in Ethylene-Bridged BODIPY Heterooligomers: From Frenkel to Förster Coupling Limit.
- Author
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Patalag LJ, Hoche J, Holzapfel M, Schmiedel A, Mitric R, Lambert C, and Werz DB
- Abstract
A series of distinct BODIPY heterooligomers (dyads, triads, and tetrads) comprising a variable number of typical green BODIPY monomers and a terminal red-emitting styryl-equipped species acting as an energy sink was prepared and subjected to computational and photophysical investigations in solvent media. An ethylene tether between the single monomeric units provides a unique foldameric system, setting the stage for a systematic study of excitation energy transfer processes (EET) on the basis of nonconjugated oscillators. The influence of stabilizing β-ethyl substituents on conformational space and the disorder of site energies and electronic couplings was addressed. In this way both the strong (Frenkel) and the weak (Förster) coupling limit could be accessed within a single system: the Frenkel limit within the strongly coupled homooligomeric green donor subunit and the Förster limit at the terminal heterosubstituted ethylene bridge. Femtosecond transient-absorption spectroscopy combined with mixed quantum-classical dynamic simulations demonstrate the limitations of the Förster resonance energy transfer (FRET) theory and provide a consistent framework to elucidate the trend of increasing relaxation lifetimes at higher homologues, revealing one of the fastest excitation energy transfer processes detected to date with a corresponding lifetime of 39 fs.
- Published
- 2021
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44. Ultrafast Energy Transfer Dynamics in a Squaraine Heterotriad.
- Author
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Lambert C, Hoche J, Schreck MH, Holzapfel M, Schmiedel A, Selby J, Turkin A, and Mitric R
- Abstract
A squaraine heterotriad consisting of three different covalently linked squaraine chromophores was synthesized, and its absorption spectra were interpreted in terms of Kasha's exciton coupling theory. Using the exciton couplings derived from model dyads (ca. 700 cm
-1 ) as the input, we were able to predict the exciton state energies of the heterotriad. Transient absorption spectroscopy with femtosecond time resolution showed that excitation of the highest exciton state populates a state mainly localized at one terminal squaraine chromophore, and energy transfer to the lowest exciton state localized at the other terminal squaraine occurs within 30 fs. Field-induced surface hopping dynamics simulations support the assumption of ultrafast energy transfer. Moreover, they show the close relationship between internal conversion and energy transfer in the intermediate to weak coupling regime. The latter is a consequence of excitation localization caused by molecular vibrations.- Published
- 2021
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45. The Optical Spectrum of Au 2 .
- Author
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Förstel M, Pollow KM, Saroukh K, Najib EA, Mitric R, and Dopfer O
- Abstract
The electronic structure of the Au
2 + cation is essential for understanding its catalytic activity. We present the optical spectrum of mass-selected Au2 + measured via photodissociation spectroscopy. Two vibrationally resolved band systems are observed in the 290-450 nm range (at ca. 440 and ca. 325 nm), which both exhibit rather irregular structure indicative of strong vibronic and spin-orbit coupling. The experimental spectra are compared to high-level quantum-chemical calculations at the CASSCF-MRCI level including spin-orbit coupling. The results demonstrate that the understanding of the electronic structure of this simple, seemingly H2 + -like diatomic molecular ion strictly requires multireference and relativistic treatment including spin-orbit effects. The calculations reveal that multiple electronic states contribute to each respective band system. It is shown that popular DFT methods completely fail to describe the complex vibronic pattern of this fundamental diatomic cation., (© 2020 The Authors. Published by Wiley-VCH GmbH.)- Published
- 2020
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46. Correlating Nanoscale Optical Coherence Length and Microscale Topography in Organic Materials by Coherent Two-Dimensional Microspectroscopy.
- Author
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Li D, Titov E, Roedel M, Kolb V, Goetz S, Mitric R, Pflaum J, and Brixner T
- Abstract
Many nanotechnology materials rely on a hierarchical structure ranging from the nanometer scale to the micrometer scale. Their interplay determines the nanoscale optical coherence length, which plays a key role in energy transport and radiative decay and, thus, the optoelectronic applications. However, it is challenging to detect optical coherence length in multiscale structures with existing methods. Techniques such as atomic force microscopy and transmission electron microscopy are not sensitive to optical coherence length. Linear absorption and fluorescence spectroscopy methods, on the other hand, were generally limited by inhomogeneous broadening, which often obstructs the determination of nanoscale coherence length. Here, we carry out coherent two-dimensional microspectroscopy to obtain a map of the local optical coherence length within a hierarchically structured molecular film. Interestingly, the nanoscale coherence length is found to correlate with microscale topography, suggesting a perspective for controlling structural coherence on molecular length scales by appropriate microscopic growth conditions.
- Published
- 2020
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47. Do Xylylenes Isomerize in Pyrolysis?
- Author
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Hirsch F, Pachner K, Fischer I, Issler K, Petersen J, Mitric R, Bakels S, and Rijs AM
- Abstract
We report infrared spectra of xylylene isomers in the gas phase, using free electron laser (FEL) radiation. All xylylenes were generated by flash pyrolysis. The IR spectra were obtained by monitoring the ion dip signal, using a IR/UV double resonance scheme. A gas phase IR spectrum of para-xylylene was recorded, whereas ortho- and meta-xylylene were found to partially rearrange to benzocyclobutene and styrene. Computations of the UV oscillator strength for all molecules were carried out and provde an explanation for the observation of the isomerization products., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)
- Published
- 2020
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48. The origin of the solvent dependence of fluorescence quantum yields in dipolar merocyanine dyes.
- Author
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Hoche J, Schulz A, Dietrich LM, Humeniuk A, Stolte M, Schmidt D, Brixner T, Würthner F, and Mitric R
- Abstract
Fluorophores with high quantum yields are desired for a variety of applications. Optimization of promising chromophores requires an understanding of the non-radiative decay channels that compete with the emission of photons. We synthesized a new derivative of the famous laser dye 4-dicyanomethylen-2-methyl-6- p -dimethylaminostyryl-4 H -pyran ( DCM ), i.e. , merocyanine 4-(dicyanomethylene)-2- tert -butyl-6-[3-(3-butyl-benzothiazol-2-ylidene)1-propenyl]-4 H -pyran ( DCBT ). We measured fluorescence lifetimes and quantum yields in a variety of solvents and found a trend opposite to the energy gap law. This motivated a theoretical investigation into the possible non-radiative decay channels. We propose that a barrier to a conical intersection exists that is very sensitive to the solvent polarity. The conical intersection is characterized by a twisted geometry which allows a subsequent photoisomerization. Transient absorption measurements confirmed the formation of a photoisomer in unpolar solvents, while the measurements of fluorescence quantum yields at low temperature demonstrated the existence of an activation energy barrier., (This journal is © The Royal Society of Chemistry 2019.)
- Published
- 2019
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49. Dynamic exciton localisation in a pyrene-BODIPY-pyrene dye conjugate.
- Author
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Auerhammer N, Schulz A, Schmiedel A, Holzapfel M, Hoche J, Röhr MIS, Mitric R, and Lambert C
- Abstract
The photophysics of a molecular triad consisting of a BODIPY dye and two pyrene chromophores attached in 2-position are investigated by steady state and fs-time resolved transient absorption spectroscopy as well as by field induced surface hopping (FISH) simulations. While the steady state measurements indicate moderate chromophore interactions within the triad, the time resolved measurements show upon pyrene excitation a delocalised excited state which localises onto the BODIPY chromophore with a time constant of 0.12 ps. This could either be interpreted as an internal conversion process within the excitonically coupled chromophores or as an energy transfer from the pyrenes to the BODIPY dye. The analysis of FISH-trajectories reveals an oscillatory behaviour where the excitation hops between the pyrene units and the BODIPY dye several times until finally they become localised on the BODIPY chromophore within 100 fs. This is accompanied by an ultrafast nonradiative relaxation within the excitonic manifold mediated by the nonadiabatic coupling. Averaging over an ensemble of trajectories allowed us to simulate the electronic state population dynamics and determine the time constants for the nonradiative transitions that mediate the ultrafast energy transfer and exciton localisation on BODIPY.
- Published
- 2019
- Full Text
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50. Diborene: Generation and Photoelectron Spectroscopy of an Inorganic Biradical.
- Author
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Schleier D, Humeniuk A, Reusch E, Holzmeier F, Nunez-Reyes D, Alcaraz C, Garcia GA, Loison JC, Fischer I, and Mitric R
- Abstract
Diborenes, R-BB-R', are of current interest in inorganic chemistry because they offer the opportunity to tune the properties of a biradical by modifying the substituents of the diborene parent, HBBH. Here we synthesize the elusive diborene by H atom abstraction from diborane, B
2 H6 , using fluorine atoms and report a vibrationally resolved photoelectron spectrum of the HBBH biradical. The spectrum is interpreted by comparison with high-level ab initio computations, taking into account the Renner-Teller splitting in the X+ 2 Π ionic ground state, which show an excellent agreement with the experimental spectrum. An adiabatic ionization energy of 9.080 ± 0.015 eV was determined, and a vibrational progression in the boron-boron stretching vibration of 0.14 eV is visible. This is due to the reduction of bond order upon ionization, accompanied by an increase of the computed boron-boron bond length, RBB , from 1.514 to 1.606 Å.- Published
- 2018
- Full Text
- View/download PDF
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