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1.
J Phys Chem C Nanomater Interfaces ; 123(42): 25908-25914, 2019 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-31673304

RESUMO

This paper describes an experimental approach to eliminating the loss of reversibility that surface-bound spiropyrans exhibit when switched with light. Although such fatigue can be controlled in other contexts, on surfaces, the photochromic compounds are held in close proximity to each other and relatively few molecules modulate the properties of a device, leading to a loss of functionality after only a few switching cycles. The switching process was characterized by photoelectron spectroscopy and differences in tunneling currents in the spiropyran and merocyanine forms using eutectic Ga-In. Self-assembled monolayers comprising only the photochromic compounds degraded rapidly, while mixed monolayers with hexanethiol showed different behaviors depending on the relative humidity. Under dry conditions, no chemical degradation was observed and the switching process was reversible over at least 100 cycles. Under humid conditions, no degradation occurred, but the switching process became irreversible. The absence of degradation observed in mixed monolayers is ascribed to the lack of solvation, which increases the barrier to a key bond rotation past the available thermal energy. These results highlight important differences in the contexts in which photochromic compounds are utilized and demonstrate that they can be leveraged to extract device-relevant functionality from surface-bound switches by suppressing fatigue and irreversibility.

2.
J Chem Phys ; 151(18): 184903, 2019 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-31731849

RESUMO

We report an investigation of structure and photophysics of thin layers of cibalackrot, a sturdy dye derived from indigo by double annulation at the central double bond. Evaporated layers contain up to three phases, two crystalline and one amorphous. Relative amounts of all three have been determined by a combination of X-ray diffraction and FT-IR reflectance spectroscopy. Initially, excited singlet state rapidly produces a high yield of a transient intermediate whose spectral properties are compatible with charge-transfer nature. This intermediate more slowly converts to a significant yield of triplet, which, however, does not exceed 100% and may well be produced by intersystem crossing rather than singlet fission. The yields were determined by transient absorption spectroscopy and corrected for effects of partial sample alignment by a simple generally applicable procedure. Formation of excimers was also observed. In order to obtain guidance for improving molecular packing by a minor structural modification, calculations by a simplified frontier orbital method were used to find all local maxima of singlet fission rate as a function of geometry of a molecular pair. The method was tested at 48 maxima by comparison with the ab initio Frenkel-Davydov exciton model.

3.
ACS Omega ; 4(15): 16481-16492, 2019 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-31616826

RESUMO

A series of poly(tetrahydrofuran)s with molecular weights above entanglement molecular weight M e were synthesized, and one of their end-groups was functionalized with a supramolecular entity so that the corresponding polymers form a brushlike structure suitable for comparison with conventional irreversible bottlebrush polymers. To compare their relaxation mechanisms, linear rheology was employed and showed that a hierarchical relaxation, which is usually observed in bottlebrush polymers, occurs in these materials, too. The polymer chain segments close to the supramolecular backbone are highly immobilized due to strong association in the center of polymer brush and cannot relax via reptation mechanism, which is mainly responsible for linear entangled polymer relaxations. Therefore, disentanglement can take much longer through contour length fluctuations and arm retraction processes similar to covalent bottlebrush polymers and combs. The relaxed ends of polymers then act as solvent to let the remaining segments of the polymeric brush undergo Rouse-like motions (constraint release Rouse). At longer times, additional plateau appears, which can be attributed to the relaxation of the entire supramolecular bottlebrush polymer via hopping or reptative motions. With an increase of temperature, viscoelastic solid behavior turns into viscoelastic liquid due to reversible depolymerization of the supramolecular backbone of the bottlebrush polymer. The elastic modulus (G' in the order of kPa) was much less than the values found for the entanglement plateau modulus of linear poly(tetrahydrofuran) (in order of MPa). This low modulus value, which exists up to very low frequencies (high temperatures), makes them a good candidate for supersoft elastomers.

4.
Biophys Chem ; 253: 106220, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31302375

RESUMO

Stabilization of G-quadruplex structures in the c-KIT promoter with the aid of ligands has become an area of great interest in potential cancer therapeutics. Understanding the binding process between ligands and G-quadruplex is essential for a discovery of selective ligands with high binding affinity to G-quadruplex. In the present work, binding mechanisms of 4-quinazolinones to c-KIT G-quadruplex were investigated theoretically by means of molecular dynamics (MD) simulations. To explore the binding affinity of ligands, binding free energy calculations were performed using the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) method. We demonstrate that the key interactions in G-quadruplex-ligand complexes are π-π stacking and hydrogen bond interactions. However, neither of these two interactions alone determines the stability of the G-quadruplex-ligand complexes; rather, it is the result of an intricate interplay between the two. To further examine the nature of the binding, a free energy decomposition analysis at residue level was carried out. The results clearly demonstrate the crucial roles of two hot spot residues (DG4 and DG8) for the binding of ligands to c-KIT G-quadruplex, and highlight the importance of the planar aromatic moiety of ligands in G-quadruplex stabilization via π-π stacking interactions. Our study can assist in the design of new derivatives of 4-quinazolinone with high binding affinity for c-KIT G-quadruplex.


Assuntos
Proteínas Proto-Oncogênicas c-kit/química , Quinazolinonas/química , Termodinâmica , Sítios de Ligação , Quadruplex G , Ligações de Hidrogênio , Ligantes , Simulação de Acoplamento Molecular , Simulação de Dinâmica Molecular , Estrutura Molecular
5.
Phys Chem Chem Phys ; 21(7): 3683-3694, 2019 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-30632554

RESUMO

The effective fragment potential (EFP) method for the efficient inclusion of solvation effects is combined with the algebraic diagrammatic construction (ADC) scheme for the second- and third-order polarisation propagator. The accuracy of these newly developed EFP-ADC(2) and EFP-ADC(3) methods is tested with respect to supermolecular ADC calculations for a selected set of small solute·solvent complexes. The EFP model for solvation introduces only marginal errors in the excitation energies and oscillator strengths of singlet as well as triplet states, which are strictly localized on the chromophore, significantly below the intrinsic errors of the parent ADC(2) and ADC(3) methods. It is only when delocalization of electron density on the solvent molecules occurs that the error in the excitation energies increases, a well-known behavior of environment models in general. Overall, EFP-ADC schemes prove to be reliable computational approaches to simulate electronic absorption spectra in solution.

6.
J Chem Phys ; 148(4): 044103, 2018 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-29390851

RESUMO

We report an implementation of non-adiabatic coupling (NAC) forces within the equation-of-motion coupled-cluster with single and double excitations (EOM-CCSD) framework via the summed-state approach. Using illustrative examples, we compare NAC forces computed with EOM-CCSD and multi-reference (MR) wave functions (for selected cases, we also consider configuration interaction singles). In addition to the magnitude of the NAC vectors, we analyze their direction, which is important for the calculations of the rate of non-adiabatic transitions. Our benchmark set comprises three doublet radical-cations (hexatriene, cyclohexadiene, and uracil), neutral uracil, and sodium-doped ammonia clusters. When the characters of the states agree among different methods, we observe good agreement between the respective NAC vectors, both in the Franck-Condon region and away. In the cases of large discrepancies between the methods, the disagreement can be attributed to the difference in the states' character, which, in some cases, is very sensitive to electron correlation, both within single-reference and multi-reference frameworks. The numeric results confirm that the accuracy of NAC vectors depends critically on the quality of the underlying wave functions. Within their domain of applicability, EOM-CC methods provide a viable alternative to MR approaches.

7.
Chemistry ; 24(1): 71-76, 2018 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-28976042

RESUMO

The synthesis and characterization of (NHC)(tricyclo[4.1.0.02,7 ]hept-1-yl)gold(I) compounds is reported. Several of these organometallic compounds could be obtained by transmetalation from the organolithium precursor to the corresponding (NHC)gold(I) chlorides. These are by far the most strained stable organogold compounds reported so far. With these new compounds we were able to efficiently and selectively accomplish the first gold-catalyzed rearrangement of organogold compounds, even better yields were obtained by the first rhodium-catalyzed rearrangement of these organogold species. (E/Z)-Mixtures of (NHC)(cyclohex-2-en-1-ylidenemethyl)gold(I) were obtained, none of the other known rearrangement products of tricycloheptanes. Additional insight into the chemical and physical properties of the strained compounds was obtained by spectroscopic and computational studies.

8.
Photochem Photobiol ; 93(1): 37-50, 2017 01.
Artigo em Inglês | MEDLINE | ID: mdl-27925218

RESUMO

Ultraviolet radiation causes two of the most abundant mutagenic and cytotoxic DNA lesions: cyclobutane pyrimidine dimers and 6-4 photoproducts. (6-4) Photolyases are light-activated enzymes that selectively bind to DNA and trigger repair of mutagenic 6-4 photoproducts via photoinduced electron transfer from flavin adenine dinucleotide anion (FADH- ) to the lesion triggering repair. This review provides an overview of the sequential steps of the repair process, that is light absorption and resonance energy transfer, photoinduced electron transfer and electron-induced splitting mechanisms, with an emphasis on the role of theory and computation. In addition, theoretical calculations and physical properties that can be used to classify specific mechanism are discussed in an effort to trace the fundamental aspects of each individual step and assist the interpretation of experimental data. The current challenges and suggested future directions are outlined for each step, concluding with a view on the future.


Assuntos
Reparo do DNA/efeitos da radiação , DNA/efeitos da radiação , Desoxirribodipirimidina Fotoliase/metabolismo , Dímeros de Pirimidina/metabolismo , Raios Ultravioleta , DNA/metabolismo , Desoxirribodipirimidina Fotoliase/química , Elétrons , Transferência de Energia , Flavina-Adenina Dinucleotídeo/química , Prótons , Dímeros de Pirimidina/química
9.
Angew Chem Int Ed Engl ; 55(17): 5175-8, 2016 Apr 18.
Artigo em Inglês | MEDLINE | ID: mdl-26996356

RESUMO

Quantum mechanics/molecular mechanics calculations are employed to assign previously recorded experimental spectroscopic signatures of the intermediates occurring during the photo-induced repair of (6-4) photolesions by photolyases to specific molecular structures. Based on this close comparison of experiment and theory it is demonstrated that the acting repair mechanism involves proton transfer from the protonated His365 to the N3' nitrogen of the lesion, which proceeds simultaneously with intramolecular OH transfer along an oxetane-like transition state.


Assuntos
Reparo do DNA , Desoxirribodipirimidina Fotoliase/metabolismo , Dímeros de Pirimidina/metabolismo , Animais , DNA/química , DNA/metabolismo , Humanos , Prótons , Dímeros de Pirimidina/química , Raios Ultravioleta
10.
J Phys Chem B ; 119(41): 13052-62, 2015 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-26402581

RESUMO

Far-red fluorescent proteins (FPs) enable deep-tissue in vivo imaging. Combining FPs with large and small Stokes shifts enables single-excitation/dual-emission multicolor applications. Using a quantum mechanics/molecular mechanics (QM/MM) scheme, we carried out a series of simulations to identify the origin of an extended Stokes shift (0.2 eV) observed in mPlum, one of the most far-red-shifted FPs. We demonstrated that the red shift of emission is largely due to the excited-state relaxation of the chromophore itself. Rigid protein environment suppresses the relaxation; however, if the hydrogen-bond network around the chromophore is sufficiently flexible, it can rearrange upon electronic excitation, allowing the chromophore to relax. The reorganization of the hydrogen-bond network is driven by changes in bonding and charge distributions of the chromophore in the excited state. The ILE65 and GLU16 residues play the most important role. The MD simulations reveal two ground-state populations with the direct (Chro-ILE65···GLU16) and water-mediated (Chro-ILE65···Wat321···GLU16) hydrogen-bond patterns. In the excited state, both populations relax to a single emitting state with the water-mediated (Chro-ILE65···Wat321···GLU16) hydrogen-bond pattern, which provides a better match for the excited-state charge distribution (the acylimine's oxygen has a larger negative charge in S1 than in S0). The extended Stokes shift arises due to the conversion of the direct hydrogen-bond pattern to the water-mediated one accompanied by large structural relaxation of the electronically excited chromophore. This conclusion is supported by calculations for the GLU16LEU mutant, which has only one hydrogen-bond pattern. Consequently, no interconversion is possible, and the computed Stokes shift is small, in agreement with the experiment. Our theoretical findings provide support to a recent study of the Stokes shifts in mPlum and its mutants.


Assuntos
Proteínas de Fluorescência Verde/química , Ligações de Hidrogênio , Simulação de Dinâmica Molecular , Teoria Quântica
11.
Macromol Rapid Commun ; 36(1): 31-7, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25451983

RESUMO

The synthesis of highly efficient two-photon uncaging groups and their potential use in functional conjugated polymers for post-polymerization modification are reported. Careful structural design of the employed nitrophenethyl caging groups allows to efficiently induce bond scission by a two-photon process through a combination of exceptionally high two-photon absorption cross-sections and high reaction quantum yields. Furthermore, π-conjugated polyfluorenes are functionalized with these photocleavable side groups and it is possible to alter their emission properties and solubility behavior by simple light irradiation. Cleavage of side groups leads to a turn-on of the fluorescence while solubility of the π-conjugated materials is drastically reduced.


Assuntos
Fluorenos/química , Corantes Fluorescentes/química , Nitrofenóis/química , Nitrobenzenos/química , Fotólise , Polimerização , Polímeros/química , Solubilidade
12.
Annu Rev Phys Chem ; 65: 275-92, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24364918

RESUMO

DNA photolyases are light-activated enzymes that repair DNA damage induced by ultraviolet (UV) radiation. UV radiation causes two of the most abundant mutagenic and cytotoxic DNA lesions: cyclobutane pyrimidine dimers and 6-4 photolesions. Photolyases selectively bind to DNA and initiate the splitting of mutagenic pyrimidine dimers via photoinduced electron transfer from a flavin adenine dinucleotide anion (FADH(-)) to the lesion triggering its repair. This review discusses the consecutive steps of the repair process, from both experimental and theoretical points of view. It covers the following issues: the process of how photolyases accommodate the lesion into their binding pockets, excitation energy transfer between two involved catalytic cofactors, photoinduced electron transfer to the lesion, the splitting of the pyrimidine dimer radical anion, and the fate of the unstable radical species created after the splitting of the thymine dimer. In particular, mechanisms of the splitting and restoration of the original bases are described in detail, and the most probable repair pathways are outlined.


Assuntos
Reparo do DNA , DNA/metabolismo , Desoxirribodipirimidina Fotoliase/metabolismo , Animais , Sítios de Ligação , DNA/química , DNA/genética , Desoxirribodipirimidina Fotoliase/química , Humanos , Luz , Modelos Moleculares
13.
Phys Chem Chem Phys ; 15(46): 19957-69, 2013 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-24145385

RESUMO

(6-4)-Photolyases are fascinating enzymes which repair (6-4)-DNA photolesions utilizing light themselves. It is well known that upon initial photo-excitation of an antenna pigment an electron is transferred from an adjacent FADH(-) cofactor to the photolesion initiating repair, i.e. restoration of the original undamaged DNA bases. Concerning the molecular details of this amazing repair mechanism, the early steps of energy transfer and catalytic electron generation are well understood, the terminal repair mechanism, however, is still a matter of ongoing debate. In this perspective article, recent results of quantum chemical investigations are presented, and their meaning for the repair mechanism under natural conditions is outlined. Consequences of natural light conditions, temperature and thermal equilibration are highlighted when issues like the initial protonation state of the relevant histidines and the lesion, or the direction of electron transfer are discussed.


Assuntos
Reparo do DNA , Desoxirribodipirimidina Fotoliase/química , Teoria Quântica , Animais , Biocatálise , DNA/química , DNA/metabolismo , Desoxirribodipirimidina Fotoliase/metabolismo , Drosophila/enzimologia , Transporte de Elétrons , Elétrons , Flavina-Adenina Dinucleotídeo/química , Raios Ultravioleta
14.
J Phys Chem B ; 117(35): 10071-9, 2013 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-23915283

RESUMO

The (6-4) photolyases are blue-light-activated enzymes that selectively bind to DNA and initiate splitting of mutagenic thymine (6-4) thymine photoproducts (T(6-4)T-PP) via photoinduced electron transfer from flavin adenine dinucleotide anion (FADH(-)) to the lesion triggering repair. In the present work, the repair mechanism after the initial electron transfer and the effect of the protein/DNA environment are investigated theoretically by means of hybrid quantum mechanical/molecular mechanical (QM/MM) simulations using X-ray structure of the enzyme-DNA complex. By comparison of three previously proposed repair mechanisms, we found that the lowest activation free energy is required for the pathway in which the key step governing the repair photocycle is electron transfer coupled with the proton transfer from the protonated histidine, His365, to the N3' nitrogen of the pyrimidone thymine. The transfer simultaneously occurs with concerted intramolecular OH transfer without formation of an oxetane or isolated water molecule intermediate. In contrast to previously suggested mechanisms, this newly identified pathway requires neither a subsequent two-photon process nor electronic excitation of the photolesion.


Assuntos
Reparo do DNA , Desoxirribodipirimidina Fotoliase/metabolismo , Modelos Moleculares , Dímeros de Pirimidina/metabolismo , Teoria Quântica , Animais , Biocatálise , DNA/química , DNA/metabolismo , Desoxirribodipirimidina Fotoliase/química , Drosophila melanogaster/enzimologia , Transporte de Elétrons , Elétrons , Luz , Prótons , Dímeros de Pirimidina/química
15.
Chemphyschem ; 14(12): 2817-24, 2013 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-23821498

RESUMO

Several strategies have evolved to repair one of the abundant UV radiation-induced damages caused to DNA, namely the mutagenic pyrimidine (6-4) pyrimidone photolesions. DNA (6-4)-photolyases are enzymes repairing these lesions by a photoinitiated electron transfer. An important aspect of a possible repair mechanism is its generality and transferability to different (6-4) lesions. Therefore, previously suggested mechanisms for the repair of the T(6-4)T lesion are here transferred to the T(6-4)C and C(6-4)T lesions and investigated theoretically using quantum chemical methods. Despite the different functional groups of the pyrimidine bases involved, a general valid molecular mechanism was identified, in which the initial step is an electron transfer coupled to a proton transfer from the protonated HIS365 to the N3(') nitrogen of the 3(') pyrimidine, followed by an intramolecular OH/NH2 transfer in one concerted step, which does not require an oxetane/azetidine or isolated water/ammonia intermediate.


Assuntos
Citosina/química , DNA/química , Desoxirribodipirimidina Fotoliase/metabolismo , Teoria Quântica , Timina/química , Raios Ultravioleta , DNA/metabolismo , Dano ao DNA , Reparo do DNA , Desoxirribodipirimidina Fotoliase/química , Transporte de Elétrons , Modelos Moleculares , Dímeros de Pirimidina/química , Termodinâmica
16.
J Phys Chem Lett ; 4(6): 943-9, 2013 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-26291360

RESUMO

Intermolecular coulombic decay (ICD) is an efficient mechanism of low-energy electron generation in condensed phases and is discussed as their potential source in living cells, tissues, and materials. The first example of ICD as an operating mechanism in real biological systems, that is, in the DNA repair enzymes photolyases, is presented. Photolyase function involves light-induced electron detachment from a reduced flavin adenine dinucleotide (FADH(-)), followed by its transfer to the DNA-lesion triggering repair of covalently bound nucleobase dimers. Modern quantum chemical methods are employed to demonstrate that the transferred electron is efficiently generated via a resonant ICD process between the antenna pigment and the FADH(-) cofactors.

17.
J Chem Phys ; 137(22): 22A531, 2012 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-23249068

RESUMO

The multi-state and multi-mode vibronic interactions between the five lowest electronic states of the title compound are investigated theoretically by an ab initio quantum dynamical approach. The well-established linear vibronic coupling scheme is adopted, augmented by quadratic coupling terms for the totally symmetric modes. The pertinent system parameters are obtained from outer valence Greens function and equation-of-motion coupled-cluster ab initio calculations. Large-scale quantum dynamical simulations are performed employing a powerful wavepacket propagation scheme. The band shapes and line structures (as far as available) of the experimental photoelectron spectra are well reproduced. Time-dependent electronic populations reveal ultrafast internal conversion processes and allow for important insight into the fluorescence properties of the radical cation. The relation to other fluoro derivatives of the benzene radical cation is discussed.

18.
J Chem Phys ; 137(13): 134302, 2012 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-23039594

RESUMO

Full dimensional multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) calculations of the dynamics of the three difluorobenzene cationic isomers in five lowest-lying doublet electronic states using the ab initio multistate multimode vibronic coupling Hamiltonian (MMVCH) model are carried out using the Heidelberg MCTDH package. The same dynamical problems, but treated with the MCTDH scheme and using a reduced dimensional ab initio MMVCH model, have been previously reported [S. Faraji, H.-D. Meyer, and H. Köppel, "Multistate vibronic interactions in difluorobenzene radical cations. II Quantum dynamical simulations," J. Chem. Phys. 129, 074311 (2008)]. For easy comparison with the reduced dimensional results, 11D or 10D ML-MCTDH calculations are also performed. Extensive ML-MCTDH test calculations are performed to find appropriate ML-MCTDH wavefunction structures (ML-trees), and the convergence of the ML-MCTDH calculations are carefully checked to ensure accurate results. Based on the appropriate ML-trees, the photoelectron (PE) spectrum and the mass analyzed threshold ionization (MATI) spectrum are simulated, analyzed, and compared with corresponding experimental spectra. Because of its efficient simulation capability for large systems, ML-MCTDH calculations save a considerable amount of central processing unit (CPU)-time, even when a reduced dimensional MMVCH is used, i.e., the same reduced model as in the corresponding MCTDH calculations. Simulations of the experimental PE spectra by full dimensional ML-MCTDH calculations reproduced main peaks, which originate from different electronic states. The agreement is improved as compared to the reduced dimensionality calculations. Unfortunately, the experimental PE spectra are not very well resolved. Therefore, we compare our calculations additionally with highly resolved MATI spectra, which, however, are only available for the X̃ state. Based on a series of ML-MCTDH simulations with longer propagation time for X̃, a number of vibrational modes, including fundamentals, their combinations, and overtones are simulated and assigned by comparing with the experimental assignments and the ab initio frequencies. Excellent correlation between the experimental and full dimensional ML-MCTDH results show that ML-MCTDH is accurate and very efficient and that the ab initio MMVCH model is very suitable for ML-MCTDH calculations.


Assuntos
Fluorbenzenos/química , Simulação de Dinâmica Molecular , Teoria Quântica , Cátions/química , Radicais Livres/química , Estereoisomerismo , Fatores de Tempo
19.
J Chem Phys ; 129(7): 074310, 2008 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-19044770

RESUMO

The multimode multistate vibronic interactions between the five lowest electronic states of all three isomers of the difluorobenzene radical cation are investigated theoretically, based on ab initio electronic structure data, and employing a well-established vibronic coupling model. The approach rests on the linear vibronic coupling scheme, augmented by quadratic coupling terms for the totally symmetric modes. The underlying ionization potentials and coupling constants are obtained from ab initio coupled-cluster calculations. Low-energy conical intersections and strong vibronic couplings are found to prevail within the sets of X-A and B-C-D cationic states, while the interactions between these two sets of states are found to be weaker and depend on the isomer. The inclusion of the aforementioned quadratic couplings is found to be essential to correctly reproduce the lowest-energy conical intersections between the two different sets of electronic states. Differences between the three isomers regarding these quantities are pointed out. The results will be used as basis for multidimensional wave-packet dynamical simulations for these coupled potential energy surfaces to be presented in the following paper (Paper II).


Assuntos
Simulação por Computador , Elétrons , Fluorbenzenos/química , Modelos Químicos , Teoria Quântica , Vibração , Algoritmos , Cátions/química , Radicais Livres/química , Eletricidade Estática
20.
J Chem Phys ; 129(7): 074311, 2008 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-19044771

RESUMO

The multistate vibronic dynamics in the X-D electronic states of all three difluorobenzene radical cations are investigated theoretically by an ab initio quantum dynamical approach. The vibronic coupling scheme and the ab initio values of the system parameters are adopted from Paper I [S. Faraji and H. Koppel, J. Chem. Phys. 129, 074310 (2008)]. Extensive calculations by wave-packet propagation have been performed with the aid of the multiconfiguration time-dependent Hartree method. Five coupled electronic potential energy surfaces and 10 (11 in the case of the orthoisomer) vibrational degrees of freedom have been included in these calculations. The nonadiabatic interactions lead to the restructuring of the photoelectron spectral envelopes. Ultrafast internal conversion processes within the electronic manifolds in question demonstrate the strength of the nonadiabatic coupling effects and complement the analogous findings for the electronic spectra. The internal conversion dynamics is characterized by a stepwise transfer of the electronic population to the lowest electronic state on a time scale of femtoseconds to picoseconds. A difference between the three isomers is found to be related to the weaker interaction between the sets of X-A and B-C-D states (with high-energy conical intersections) in the meta isomer, as compared to the other isomers. The implications of these findings for the qualitative understanding of the fluorescence dynamics of fluorinated benzene radical cations are discussed.


Assuntos
Simulação por Computador , Elétrons , Fluorbenzenos/química , Modelos Químicos , Teoria Quântica , Vibração , Algoritmos , Cátions/química , Radicais Livres/química
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