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1.
J Comput Chem ; 40(29): 2530-2538, 2019 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-31294857

RESUMO

Seven free base porphyrins employed in dye-sensitized photoelectrosynthetic cells are investigated with the aim of benchmarking the ability of different density functional theory (DFT) and time-dependent DFT approaches in reproducing their structure, vertical, and E0-0 excitation energies and the energy levels alignment (red-ox properties) at the interface with the TiO2 . We find that both vertical and E0-0 excitation energies are accurately reproduced by range-separated functionals, among which the ωB97X-D delivers the lowest absolute deviations from experiments. When the dye/TiO2 interface is modeled, the physical interfacial energetics is only obtained when the B3LYP functional is employed; on the other hand, M06-2X (54% of exchange) and the two long-range corrected approaches tested (CAM-B3LYP and ωB97X-D) excessively destabilize the semiconductor conduction band levels with respect to the dye's lowest unoccupied molecular orbitals (LUMOs), predicting no pathway for electron injection. © 2019 Wiley Periodicals, Inc.

2.
J Phys Chem B ; 123(26): 5514-5523, 2019 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-31192599

RESUMO

We report on the electronic absorption spectra, conformational behavior, and intra- and intermolecular hydrogen bonds of 2,3-(dibenzimidazol-2-yl)-quinoxaline (DBIQ). The experimentally found strong solvent dependence of the absorption spectra of DBIQ solutions cannot be assigned to electronic excitations of the equilibrium ground-state DBIQ structure. Extended consideration including the nonequilibrium structures within the framework of ab initio molecular dynamics (MD) revealed the importance of torsion molecular motions not covered by the static case. The strong impact of solute-solvent hydrogen bonding on stabilization of these nonequilibrium structures and on conformational composition of DBIQ was demonstrated. A presence of twisted nonplanar geometries along the whole MD trajectory was shown to drastically influence not only energies but also characters of electronic excitations, resulting in a change of local π-π* character in a solution of 1,2-dichloroethane to charge-transfer character in polar dimethylsulfoxide.

3.
Dalton Trans ; 48(29): 10915-10926, 2019 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-31149683

RESUMO

Ligand field enhancing N-heterocyclic carbene (NHC) ligands were recently shown to prevent photo-induced spin crossover in Fe(ii) complexes due to their intricate effects on the electronic excited state structure. Due to their pico- to nanosecond lifetimes, these complexes are now good candidates for photo-sensitizing applications. Herein we report the synthesis and photophysical characterization of a new family of homoleptic Fe(ii) complexes with C^N^C ligands involving diazines as the central N-heteroaromatic ligand. For these four carbene bond complexes, ultrafast transient absorption spectroscopy revealed a significant improvement of the excited-state lifetime. A record 32 ps lifetime was measured for a complex bearing a ligand combining a π-deficient pyrazine nucleus and a benzimidazolylidene as NHC. When compared to other azine-based ligands investigated, we argue that the lifetimes are modulated by a small excited state barrier expressing the ability of the ligand to reach the Fe-N distance needed for internal conversion to the ground state.

4.
Inorg Chem ; 58(8): 5069-5081, 2019 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-30950264

RESUMO

The control of photophysical properties of iron complexes and especially of their excited states decay is a great challenge in the search for sustainable alternatives to noble metals in photochemical applications. Herein we report the synthesis and investigations of the photophysics of mer and fac iron complexes bearing bidentate pyridyl-NHC ligands, coordinating the iron with three ligand-field-enhancing carbene bonds. Ultrafast transient absorption spectroscopy reveals two distinct excited state populations for both mer and fac forms, ascribed to the populations of the T1 and the T2 states, respectively, which decay to the ground state via parallel pathways. We find 3-4 ps and 15-20 ps excited-state lifetimes, with respective amplitudes depending on the isomer. The longer lifetime exceeds the one reported for iron complexes with tridentate ligands analogues involving four iron-carbene bonds. By combining experimental and computational results, a mechanism based on the differential trapping of the triplet states in spin-crossover regions is proposed for the first time to explain the impact of the fac/ mer isomerism on the overall excited-state lifetimes. Our results clearly highlight the impact of bidentate pyridyl-NHC ligands on the photophysics of iron complexes, especially the paramount role of fac/ mer isomerism in modulating the overall decay process, which can be potentially exploited in the design of new Fe(II)-based photoactive compounds.

5.
Inorg Chem ; 57(16): 10431-10441, 2018 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-30063338

RESUMO

The synthesis and the steady-state absorption spectrum of a new pyridine-imidazolylidene Fe(II) complex (Fe-NHC) are presented. A detailed mechanism of the triplet metal-to-ligand charge-transfer states decay is provided on the basis of minimum energy path (MEP) calculations used to connect the lowest-lying singlet, triplet, and quintet state minima. The competition between the different decay pathways involved in the photoresponse is assessed by analyzing the shapes of the obtained potential energy surfaces. A qualitative difference between facial ( fac) and meridional ( mer) isomers' potential energy surface (PES) topologies is evidenced for the first time in iron-based complexes. Indeed, the mer complex shows a steeper triplet path toward the corresponding 3MC minimum, which lies at a lower energy as compared to the fac isomer, thus pointing to a faster triplet decay of the former. Furthermore, while a major role of the metal-centered quintet state population from the triplet 3MC region is excluded, we identify the enlargement of iron-nitrogen bonds as the main normal modes driving the excited-state decay.

6.
Front Chem ; 6: 86, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29666792

RESUMO

Bio-macromolecules as DNA, lipid membranes and (poly)peptides are essential compounds at the core of biological systems. The development of techniques and methodologies for their characterization is therefore necessary and of utmost interest, even though difficulties can be experienced due to their intrinsic complex nature. Among these methods, spectroscopies, relying on optical properties are especially important to determine their macromolecular structures and behaviors, as well as the possible interactions and reactivity with external dyes-often drugs or pollutants-that can (photo)sensitize the bio-macromolecule leading to eventual chemical modifications, thus damages. In this review, we will focus on the theoretical simulation of electronic spectroscopies of bio-macromolecules, considering their secondary structure and including their interaction with different kind of (photo)sensitizers. Namely, absorption, emission and electronic circular dichroism (CD) spectra are calculated and compared with the available experimental data. Non-linear properties will be also taken into account by two-photon absorption, a highly promising technique (i) to enhance absorption in the red and infra-red windows and (ii) to enhance spatial resolution. Methodologically, the implications of using implicit and explicit solvent, coupled to quantum and thermal samplings of the phase space, will be addressed. Especially, hybrid quantum mechanics/molecular mechanics (QM/MM) methods are explored for a comparison with solely QM methods, in order to address the necessity to consider an accurate description of environmental effects on spectroscopic properties of biological systems.

7.
J Chem Theory Comput ; 14(5): 2570-2585, 2018 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-29614854

RESUMO

Accurate characterization of the high-lying excited state manifolds of organic molecules is of fundamental importance for the interpretation of the rich response detected in time-resolved nonlinear electronic spectroscopies. Here, we have characterized the singlet excited state manifold of benzophenone (BP), a versatile organic photoinitiator and a well-known DNA photosensitizer. Benchmarks of various multiconfigurational/multireference (RASSCF/PT2) and time-dependent density functional theory (TD-DFT) approaches allowed assignments of experimental linear absorption signals of BP in the ultraviolet (UV) region, with unprecedented characterization of ground state absorptions in the far UV. Experimental transient absorption spectra obtained by UV-vis pump-probe spectroscopy at very short time delays are shown to be directly comparable to theoretical estimates of excited state absorptions (from the low-lying nOπ* and ππ* singlet states) in the Franck-Condon region. Multireference computations provided reliable interpretation of the PP spectra, with TD-DFT results yielding a fair agreement as long as electronic transitions featuring double excitations contributions are not involved. These results lay the groundwork for further computational studies and interpretation of experimental nonlinear electronic spectra of benzophenone in more complex systems, such as BP/DNA adducts.

8.
Photochem Photobiol Sci ; 17(3): 323-331, 2018 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-29383356

RESUMO

Benzophenone (BP) despite its relatively simple molecular structure is a paradigmatic sensitizer, featuring both photocatalytic and photobiological effects due to its rather complex photophysical properties. In this contribution we report an original theoretical approach to model realistic, ultra-fast spectroscopy data, which requires describing intra- and intermolecular energy and structural relaxation. In particular we explicitly simulate time-resolved pump-probe spectra using a combination of state-of-the art hybrid quantum mechanics/molecular mechanics dynamics to treat relaxation and vibrational effects. The comparison with experimental transient absorption data demonstrates the efficiency and accuracy of our approach. Furthermore the explicit inclusion of the solvent, water for simulation and methanol for experiment, allows us, despite the inherent different behavior of the two, to underline the role played by the H-bonding relaxation in the first hundreds of femtoseconds after optical excitation. Finally we predict for the first time the two-dimensional electronic spectrum (2DES) of BP taking into account the vibrational effects and hence modelling partially symmetric and asymmetric ultrafast broadening.

9.
J Chem Phys ; 147(2): 024108, 2017 Jul 14.
Artigo em Inglês | MEDLINE | ID: mdl-28711042

RESUMO

We report a theoretical study on the analysis of the relaxed one-particle difference density matrix characterizing the passage from the ground to the excited state of a molecular system, as obtained from time-dependent density functional theory. In particular, this work aims at using the physics contained in the so-called Z-vector, which differentiates between unrelaxed and relaxed difference density matrices to analyze excited states' nature. For this purpose, we introduce novel quantum-mechanical quantities, based on the detachment/attachment methodology, for analysing the Z-vector transformation for different molecules and density functional theory functionals. A derivation pathway of these novel descriptors is reported, involving a numerical integration to be performed in the Euclidean space on the density functions. This topological analysis is then applied to two sets of chromophores, and the correlation between the level of theory and the behavior of our descriptors is properly rationalized. In particular, the effect of range-separation on the relaxation amplitude is discussed. The relaxation term is finally shown to be system-specific (for a given level of theory) and independent of the number of electrons (i.e., the relaxation amplitude is not simply the result of a collective phenomenon).

10.
J Mol Model ; 23(6): 173, 2017 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-28466425

RESUMO

We propose a new self-consistent field (SCF) algorithm based on an iterative, partially stochastic "Divide & Conquer"-type approach. This new SCF algorithm is a simple variant of the usual SCF procedure and can be easily implemented in parallel. A detailed description of the algorithm is reported. We illustrate this new method on one-dimensional hydrogen chains and three-dimensional hydrogen clusters. Graphical Abstract Stochastic partition of the molecular orbitals.

11.
Phys Chem Chem Phys ; 18(40): 28069-28081, 2016 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-27711638

RESUMO

The first combined theoretical and photovoltaic characterization of both homoleptic and heteroleptic Fe(ii)-carbene sensitized photoanodes in working dye sensitized solar cells (DSSCs) has been performed. Three new heteroleptic Fe(ii)-NHC dye sensitizers have been synthesized, characterized and tested. Despite an improved interfacial charge separation in comparison to the homoleptic compounds, the heteroleptic complexes did not show boosted photovoltaic performances. The ab initio quantitative analysis of the interfacial electron and hole transfers and the measured photovoltaic data clearly evidenced fast recombination reactions for heteroleptics, even associated with un unfavorable directional electron flow, and hence slower injection rates, in the case of homoleptics. Notably, quantum mechanics calculations revealed that deprotonation of the not anchored carboxylic function in the homoleptic complex can effectively accelerate the electron injection rate and completely suppress the electron recombination to the oxidized dye. This result suggests that introduction of strong electron-donating substituents on the not-anchored carbene ligand in heteroleptic complexes, in such a way of mimicking the electronic effects of the carboxylate functionality, should yield markedly improved interfacial charge generation properties. The present results, providing for the first time a detailed understanding of the interfacial electron transfers and photovoltaic characterization in Fe(ii)-carbene sensitized solar cells, open the way to a rational molecular engineering of efficient iron-based dyes for photoelectrochemical applications.

12.
Phys Chem Chem Phys ; 18(18): 12550-6, 2016 05 14.
Artigo em Inglês | MEDLINE | ID: mdl-27086578

RESUMO

Herein we report the synthesis and time-resolved spectroscopic characterization of a homoleptic Fe(ii) complex exhibiting a record (3)MLCT lifetime of 26 ps promoted by benzimidazolylidene-based ligands. Time dependent density functional molecular modeling of the triplet excited state manifold clearly reveals that, at equilibrium geometries, the lowest (3)MC state lies higher in energy than the lowest (3)MLCT one. This unprecedented energetic reversal in a series of iron complexes, with the stabilization of the charge-transfer state, opens up new perspectives towards iron-made excitonic and photonic devices, hampering the deactivation of the excitation via metal centered channels.

13.
J Phys Chem B ; 120(12): 3113-21, 2016 Mar 31.
Artigo em Inglês | MEDLINE | ID: mdl-26943487

RESUMO

We report on the comparison between the computational and experimental determination of electronic circular dichroism spectra of different guanine quadruplexes obtained from human telomeric sequences. In particular the difference between parallel, antiparallel, and hybrid structures is evidenced, as well as the induction of transitions between the polymorphs depending on the solution environment. Extensive molecular dynamics simulations (MD) are used to probe the conformational space of the different quadruplexes, and subsequently state-of-the-art hybrid quantum mechanics/molecular mechanics (QM/MM) techniques coupled with excitonic semiempirical Hamiltonian are used to simulate the macromolecular induced circular dichroism. The coupling of spectroscopy and molecular simulation allows an efficient one-to-one mapping between structures and optical properties, offering a way to disentangle the rich, yet complicated, quantity of information embedded in circular dichroism spectra. We show that our methodology is robust and efficient and allows us to take into account subtle conformational changes. As such, it could be used as an efficient tool to investigate structural modification upon DNA/drug interactions.


Assuntos
DNA/química , Quadruplex G , Simulação de Dinâmica Molecular , Dicroísmo Circular , Humanos , Conformação de Ácido Nucleico , Teoria Quântica
14.
J Phys Chem Lett ; 6(4): 576-80, 2015 Feb 19.
Artigo em Inglês | MEDLINE | ID: mdl-26262469

RESUMO

Benzophenone, the parent of the diarylketone family, is a versatile compound commonly used as a UV blocker. It may also trigger triplet-based DNA photosensitization. Therefore, benzophenone is involved in DNA photodamage induction. In the absence of experimentally resolved structure, the mechanism of DNA damage production remains elusive. Employing a hybrid quantum mechanics/molecular mechanics approach, here we address the spin transfer mechanism between this drug and proximal thymine, that is, the DNA nucleobase most prone to suffer triplet damages.


Assuntos
Benzofenonas/química , DNA/química , Fármacos Fotossensibilizantes/química , Simulação de Dinâmica Molecular , Teoria Quântica
15.
Front Chem ; 3: 67, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26734600

RESUMO

We report the characterization of the interaction between B-DNA and three terpyridin iron II complexes. Relatively long time-scale molecular dynamics (MD) is used in order to characterize the stable interaction modes. By means of molecular modeling and UV-vis spectroscopy, we prove that they may lead to stable interactions with the DNA duplex. Furthermore, the presence of larger π-conjugated moieties also leads to the appearance of intercalation binding mode. Non-covalent stabilizing interactions between the iron complexes and the DNA are also characterized and evidenced by the analysis of the gradient of the electronic density. Finally, the structural deformations induced on the DNA in the different binding modes are also evidenced. The synthesis and chemical characterization of the three complexes is reported, as well as their absorption spectra in presence of DNA duplexes to prove the interaction with DNA. Finally, their effects on human cell cultures have also been evidenced to further enlighten their biological effects.

16.
Chemistry ; 20(40): 12901-9, 2014 Sep 26.
Artigo em Inglês | MEDLINE | ID: mdl-25145959

RESUMO

The environmental effects on the structural and photophysical properties of [Ru(L)2 (dppz)](2+) complexes (L=bpy=2,2'-bipyridine, phen=1,10-phenanthroline, tap=1,4,5,8-tetraazaphenanthrene; dppz=dipyrido[3,3-a:2',3'-c]phenazine), used as DNA intercalators, have been studied by means of DFT, time-dependent DFT, and quantum mechanics/molecular mechanics calculations. The electronic characteristics of the low-lying triplet excited states in water, acetonitrile, and DNA have been investigated to decipher the influence of the environment on the luminescent behavior of this class of molecules. The lowest triplet intra-ligand (IL) excited state calculated at λ≈800 nm for the three complexes and localized on the dppz ligand is not very sensitive to the environment and is available for electron transfer from a guanine nucleobase. Whereas the lowest triplet metal-to-ligand charge-transfer ((3)MLCT) states remain localized on the ancillary ligand (tap) in [Ru(tap)2 (dppz)](2+), regardless of the environment, their character is drastically modified in the other complexes [Ru(phen)2 (dppz)](2+) and [Ru(bpy)2 (dppz)](2+) upon going from acetonitrile (MLCTdppz/phen or MLCTdppz/bpy) to water (MLCTdppz) and DNA (MLCTphen and MLCTbpy). The change in the character of the low-lying (3) MLCT states accompanying nuclear relaxation in the excited state controls the emissive properties of the complexes in water, acetonitrile, and DNA. The light-switching effect has been rationalized on the basis of environment-induced control of the electronic density distributed in the lowest triplet excited states.


Assuntos
2,2'-Dipiridil/química , DNA/química , Substâncias Intercalantes/química , Compostos Organometálicos/química , Fenantrenos/química , Fenantrolinas/química , Fenazinas/química , Rutênio/química , 2,2'-Dipiridil/farmacologia , Substâncias Intercalantes/farmacologia , Luminescência , Modelos Moleculares , Compostos Organometálicos/farmacologia , Fenantrenos/farmacologia , Fenantrolinas/farmacologia , Fenazinas/farmacologia , Rutênio/farmacologia
17.
J Comput Chem ; 35(15): 1131-9, 2014 Jun 05.
Artigo em Inglês | MEDLINE | ID: mdl-24752947

RESUMO

Experimental X-ray absorption spectra are extensively used to determine electronic structure of small molecules but remain difficult to exploit for proteins due to the large number of peaks within their spectra. For such complex systems, theoretical tools like quantum mechanics/molecular mechanics methodology can greatly ease the assignment of the spectra. This study presents a systematic methodology to evaluate core-ionization energies (E(ion)) in proteins with the help of the asymptotic projection approach (Glushkov and Tsaune, Z. Vichislit. Matem. Mat. Fiz. 1985, 25, 298; Glushkov, Chem. Phys. Lett. 1997, 273, 122; Glushkov, Chem. Phys. Lett. 1998, 287, 189; Glushkov, J. Math. Chem. 2002, 31, 91; Glushkov, Opt. Spectrosc. 2002, 93, 15). An in-depth inspection of E(ion) of systems of increasing complexity is considered, going from amino acids to polyglycine and to glycine in human serum albumin (HSA). Computational analysis can help to better understand experimental data and to discriminate environmental effects by tracing them back to individual and collective electrostatic contributions. In the present work, it was found that E(ion) of alpha carbon of glycine residues in HSA ranges from 285 to 295 eV depending on their surroundings.


Assuntos
Proteínas/química , Espectroscopia por Absorção de Raios X/métodos , Aminoácidos/química , Simulação por Computador , Íons , Modelos Químicos , Modelos Moleculares , Compostos Orgânicos , Conformação Proteica
18.
J Mol Model ; 20(3): 2082, 2014 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-24562852

RESUMO

The synthesis of a new Ru(II) complex is reported. Its absorption spectrum when interacting with DNA in water was calculated at the hybrid quantum mechanics molecular mechanics level of theory and compared with experimental data. The vertical transitions were computed using time-dependent density functional theory in the linear response approximation. The complex and its environment were treated at the quantum mechanical and molecular mechanical levels, respectively. The effects of the environment were investigated in detail and conveniently classified into electrostatic and polarization effects. The latter were modeled using the computationally inexpensive "electronic response of the surroundings" method. It was found that the main features of the experimental spectrum are nicely reproduced by the theoretical calculations. Moreover, analysis of the most intense transitions utilizing the natural transition orbital formalism revealed important insights into their nature and their potential role in the irreversible oxidation of DNA, a phenomenon that could be relevant in the field of cancer therapy.


Assuntos
Complexos de Coordenação/química , DNA de Forma B/química , Simulação de Dinâmica Molecular , Compostos Organometálicos/química , Rutênio/química , Espectrofotometria/métodos , Complexos de Coordenação/síntese química , Complexos de Coordenação/metabolismo , DNA de Forma B/metabolismo , Substâncias Intercalantes/química , Substâncias Intercalantes/metabolismo , Modelos Químicos , Estrutura Molecular , Conformação de Ácido Nucleico , Compostos Organometálicos/síntese química , Compostos Organometálicos/metabolismo , Teoria Quântica , Eletricidade Estática , Água/química
19.
J Comput Chem ; 35(4): 313-23, 2014 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-24403018

RESUMO

We further develop an idea to generate a compact multireference space without first solving the configuration interaction problem previously proposed for the ground state (GS) (Glushkov, Chem. Phys. Lett. 1995, 244, 1). In the present contribution, our attention is focused on low-lying excited states (ESs) with the same symmetry as the GS which can be adequately described in terms of an high-spin open-shell formalism. Two references Møller-Plesset (MP) like perturbation theory for ESs is developed. It is based on: (1) a main reference configuration constructed from the parent molecular orbitals adjusted to a given ES and (2) secondary double excitation configuration built on the GS like orbitals determined by the Hartree-Fock equations subject to some orthogonality constraints. It is shown how to modify the MP zeroth-order Hamiltonian so that the reference configurations and corresponding excitations are eigenfunctions of it and are compatible with orthogonality conditions for the GS and ES. Intruder states appearance is also discussed. The proposed scheme is applied to the GS, ES, and excitation energies of small molecules to illustrate and calibrate our calculations.

20.
J Chem Theory Comput ; 10(9): 3896-905, 2014 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-26588533

RESUMO

We hereby report studies devoted to a topological descriptor of photoinduced electronic charge density variation. Our novel index, symbolized as ϕS, consists in the detachment and attachment densities overlap, where the detachment density physically depicts the electron density removed from the ground state of a molecule during the transition while the attachment density consists in the rearranged density in the excited state. Our method provides a simple and efficient way to quantitatively evaluate how easy the charge-separation is made upon the chromophore's light absorption. Furthermore, this model can be applied for instance to address a comment on new push-pull dyes charge-transfer ability in order to assess their potentiality as candidates for light absorption-based devices. Moreover, the ϕS assessment allows us to perform some methodological diagnostic tests concerning the use of long-range corrected exchange-correlation functional in a time-dependent density functional theory (TDDFT) framework. This paper relates the ϕS descriptor's mathematical foundations from various perspectives (detachment/attachment densities or natural transition orbitals), together with its application to several types of chromophores. Connections and divergences with a formerly proposed index are finally evidenced.

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