Showing papers by "Demetrio A. da Silva Filho published in 2017"
TL;DR: In this paper, a series of fluorenone-centered compounds of increasing size were analyzed by means of density functional theory (DFT) calculations and experimental characterizations, and it was shown that while the absorption energy band is intrinsically related to a π-π* transition between orbitals strongly localized on the fluorenon core, its position and intensity are affected by the tendency of these compounds to associate/aggregate in their ground state even in solution.
Abstract: Fluorenone-based compounds usually emit light in the yellow-red region. While different origins have been assigned to these colors, only a few studies make a direct correlation between the characteristic emission and the lowest absorption energy band (LEB). Intriguingly, striking similarities can be observed in the position, shape, and intensity of the LEB for such compounds with different molecular sizes. This work is focused on these aspects of absorption and emission spectra, by means of density functional theory (DFT) calculations and experimental characterizations of a series of fluorenone-centered compounds of increasing size. Our results show that while the absorption LEB is intrinsically related to a π–π* transition between orbitals strongly localized on the fluorenone core, its position and intensity are affected by the tendency of these compounds to associate/aggregate in their ground state even in solution. The intermolecular CO···HC (aromatic) hydrogen bonds (H-bonds) redshift the absorption m...
32 citations
TL;DR: The authors' simulations suggest that the Franck–Condon approximation may not be suitable to appropriately characterize the vibronic progression of these molecules, whereas the NE approach provides a contribution that vary from negligible to meaningful depending on which molecule and energy region is under analysis.
Abstract: We systematically investigate, at density functional theory level, the electronic properties of a set of ten carotenoid molecules with different conjugation length. Ground state geometries were fully optimized using both B3LYP and its long-range corrected version, i.e., the CAM-B3LYP functional. The time-dependent DFT approach (TD-DFT) was also performed for the calculation of the excited states of the optimized geometries and the results were compared to the experimental ones, when available. Our findings indicate a dependence of the transition vertical energies, oscillator strengths, and transition dipole moments on the extension of conjugation, as expected. We also investigate the impact of the intra-molecular vibrations on the absorption spectrum by means of the Franck-Condon (FC) and nuclear ensemble (NE) approach to spectra simulation. Our simulations suggest that the Franck-Condon approximation may not be suitable to appropriately characterize the vibronic progression of these molecules, whereas the NE approach provides a contribution that vary from negligible to meaningful depending on which molecule and energy region is under analysis.
16 citations
TL;DR: The results suggest that correcting the long-range term on exchange term of the Coulomb operator, by means of a tuning procedure, is a good option to accurately describe properties of the phthalocyanine molecule.
Abstract: By means of Density functional theory and time-dependent density functional theory calculations, we present a comprehensive investigation on the influence of different functional schemes on electronic and optical properties of the phthalocyanine molecule. By carrying out our own tuning on the OT-LC-BLYP/6-31G(d,p) functional, we show that such a procedure is fundamental to accurately match experimental results. We compare our results to several others available in the literature, including the B3LYP/6-31+G(d,p) set, which is commonly portrayed as the best combination in order to obtain a good description of the band gap. The results obtained here present not only significant improvement of the optical properties from the conventional BLYP, but we can also objectively report an improvement of our tuned functional when compared to the current benchmark of the literature as far as optical properties are concerned. Particularly, by means of this approach, it was possible to achieve a good agreement between the theoretical and experimental optical gap as well as of the positioning of the main peaks in the absorption spectrum. Our results thus suggest that correcting the long-range term on exchange term of the Coulomb operator, by means of a tuning procedure, is a good option to accurately describe properties of the phthalocyanine molecule.
13 citations
TL;DR: The results show that the insertion of ethynyl spacers between the central aromatic core and the flexible peripheral chains results in lower reorganization energies and enhanced intermolecular order within the stacks with a preferred cofacial 60° staggered conformation, which would result in high charge-carrier mobilities in good agreement with the experimental data.
Abstract: We have performed a multiscale approach to study the influence of peripheral substitution in the semiconducting properties of discotic liquid-crystalline triindoles. Charge carrier mobility as high as 1.4 cm2 V−1 s−1 was experimentally reported for triindoles substituted with alkynyl chains on the periphery (Gomez-Lor et al. Angew. Chem., Int. Ed., 2011, 50, 7399–7402). In this work, our goal is to get a deeper understanding of both the molecular electronic structure and microscopic factors affecting the charge transport properties in triindoles as a function of the spacer group connecting the central cores with the external alkyl chains (i.e., alkyne or phenyl spacers groups). To this end, we first perform Quantum Mechanical (QM) calculations to assess how the peripheral substitution affects the electronic structure and the internal reorganization energy. Secondly, boxes of stacked molecules were built and relaxed through molecular dynamics to obtain realistic structures. Conformational analysis and calculations of transfer integrals for closed neighbours were performed. Our results show that the insertion of ethynyl spacers between the central aromatic core and the flexible peripheral chains results in lower reorganization energies and enhanced intermolecular order within the stacks with a preferred cofacial 60° staggered conformation, which would result in high charge-carrier mobilities in good agreement with the experimental data. This work allows a deeper understanding of charge carrier mobility in columnar phases, linking the structural order at the molecular level to the property of interest, i.e. the charge carrier mobility. We hope that this understanding will improve the design of systems at the supramolecular level aiming at obtaining a more defined conducting channel, higher mobility and smaller fluctuations within the column.
8 citations
TL;DR: In this paper, a study of electron mobility in a PCBM system is performed by means of analytical considerations and Kinetic Monte Carlo simulations, and the relative importance of these environmental effects is analyzed in details, furthermore the predicted mobilities are compared with experimental results and similar simulations performed in C60.
8 citations
TL;DR: A hybrid methodology of combining Uncoupled Monte Carlo Simulations (UMC) and Density functional Theory (DFT) methodologies to obtain a good compromise between computational feasibility and accuracy is proposed and it is concluded that such methodology might be an important tool towards the description of systems with higher complexity.
Abstract: Pentacene is an organic semiconductor that draws special attention from the scientific community due to the high mobility of its charge carriers. As electron-hole interactions are important aspects in the regard of such property, a computationally inexpensive method to predict the coupling between these quasi-particles is highly desired. In this work, we propose a hybrid methodology of combining Uncoupled Monte Carlo Simulations (UMC) and Density functional Theory (DFT) methodologies to obtain a good compromise between computational feasibility and accuracy. As a first step in considering a Pentacene crystal, we describe its unit cell: the Pentacene Dimer. Because many conformations can be encountered for the dimer and considering the complexity of the system, we make use of UMC in order to find the most probable structures and relative orientations for the Pentacene-Pentacene complex. Following, we carry out electronic structure calculations in the scope of DFT with the goal of describing the electron-hole coupling on the most probable configurations obtained by UMC. The comparison of our results with previously reported data on the literature suggests that the methodology is well suited for describing transfer integrals of organic semiconductors. The observed accuracy together with the smaller computational cost required by our approach allows us to conclude that such methodology might be an important tool towards the description of systems with higher complexity.
4 citations
TL;DR: The measurements indicate that, indeed, the material system of Myrcia sylvatica essential oil may be successfully employed for the design of organic photovoltaic devices.
Abstract: We present an extensive study of the optical properties of Myrcia sylvatica essential oil with the goal of investigating the suitability of its material system for uses in organic photovoltaics. The methods of extraction, experimental analysis, and theoretical modeling are described in detail. The precise composition of the oil in our samples is determined via gas chromatography, mass spectrometry, and X-ray scattering techniques. The measurements indicate that, indeed, the material system of Myrcia sylvatica essential oil may be successfully employed for the design of organic photovoltaic devices. The optical absorption of the molecules that compose the oil are calculated using time-dependent density functional theory and used to explain the measured UV-Vis spectra of the oil. We show that it is sufficient to consider the α-bisabolol/cadalene pair, two of the main constituents of the oil, to obtain the main features of the UV-Vis spectra. This finding is of importance for future works that aim to use Myrcia sylvatica essential oil as a photovoltaic material.
3 citations
TL;DR: Investigating optical and electronic structure changes in the phthalocyanine profiles in the presence of different metals is of fundamental importance for evaluating the appropriateness of the resulting system as far as these uses are concerned.
Abstract: Phthalocyanines represent a crucial class of organic compounds with high technological appeal. By doping the center of these systems with metals, one obtains the so-called metal-phthalocyanines, whose property of being an effective electron donor allows for potentially interesting uses in organic electronics. In this sense, investigating optical and electronic structure changes in the phthalocyanine profiles in the presence of different metals is of fundamental importance for evaluating the appropriateness of the resulting system as far as these uses are concerned. In the present work, we carry out this kind of effort for phthalocyanines doped with different metals, namely, copper, nickel, and magnesium. Density functional theory was applied to obtain the absorption spectra, and electronic and structural properties of the complexes. Our results suggest that depending on the dopant, a different level of change is achieved. Moreover, electrostatic potential energy mapping shows how the charge distribution can be affected by solar radiation. Our contribution is crucial in describing the best possible candidates for use in different organic photovoltaic applications. Graphical Abstract Representation of meta-phthalocyanine systems. All calculations of this work are based on varying metal position along z axis, considering the z-axis has its zero point matching with the center of phthalocyanine cavityconsidering.
2 citations
TL;DR: It is shown that the most important feature of a DFT calculation is the appropriate selection of long-range corrected functionals, which allows for the accurate description of the first absorption band of these molecules.
Abstract: Acene-thiophenes compounds have been used successfully as active materials in thin-film transistors and photodetectors. This work aims at obtaining an adequate theoretical framework to accurately characterize the optical and electronic properties of two such compounds: NaT2 and NaT3. This is done by comparing the results of simulations with experimental absorption spectra. Basis size effects are investigated as well as the role of intramolecular vibrations in the simulated spectra. It is shown that the most important feature of a DFT calculation is the appropriate selection of long-range corrected functionals, which allows for the accurate description of the first absorption band of these molecules.
1 citations
TL;DR: It is obtained that simulations in the framework of PCM do not provide a fair description of the real system and may pave the way for better descriptions of some optoelectronic properties of interest in polymer/solvent systems.
Abstract: The optical properties of polymer/solvent systems composed by the polymers P3HT and PolyeraActivInk N2200 under the present of chloroform as solvent are experimentally and theoretically investigated using UV-Vis spectroscopy, molecular dynamics (MD), and density functional theory (DFT) calculations. The study is focused on obtaining the theoretical methodologies that properly describes the experimentally obtained absorption spectra of polymer-solvent complexes. In order to investigate the solvent influence, two different approaches are taken into account: the solvation shell method (SSM) and the polarizable continuum model (PCM). Our findings shown that SSM simulations, which combine MD and DFT calculations, are in good agreement with the experimental data. Moreover, it is obtained that simulations in the framework of PCM do not provide a fair description of the real system. Importantly, these results may pave the way for better descriptions of some optoelectronic properties of interest in polymer/solvent systems. Graphical Abstract ᅟ.