1,720,973 research outputs found
Electronic and optical properties of nanometer-sized chromophores in bacterial cellulose
Full text linkWe present a computational investigation on the electronic and optical properties of the principal chromophores found in bacterial
cellulose (BC). We focus on the three key structures that were isolated from aged BC: (A) 2,5Dihydroxy[
1,4]benzoquinone, (B) 5,8Dihydroxy[
1,4]naphthoquinone (C) 2,5Dihydroxyacetophenone,
while (D) p-benzoquinone was used as a reference structure. For all
the isolated molecules, we performed allelectrons
Density Functional Theory (DFT) and Time Dependent DFT (TDDFT)
calculations with a localized Gaussian basisset
and the hybrid exchangecorrelation
functionals B3LYP and PBE0. We computed and
analyzed their electronic and optical properties and compare with available experimental data
Effects of substitution and functionalization on the electronic, optical, and transport properties of polycyclic aromatic hydrocarbons
No full textThe electronic and optical properties of some represenative molecules belonging to the PAHs
family of interest for solid state applications have been studied within a (TD)DFT
scheme. We focus in particular on Pentacene, Pyrene and two Dibenzochrysenes (angular and
compact).For the isolated gas-phase molecules we performed all-electrons Density Functional
Theory (DFT) and Time Dependent DFT (TDDFT)
calculations with a localized Gaussian basis-set and the hybrid B3LYP exchange-correlation
functional [1],[2]. Electron affinities, ionization energies, fundamental energy-gaps, optical
absorption spectra, exciton binding energies, and reorganization energies
for holes and electrons have been calculated and compared with the available
experimental/theoretical data for the pure molecules and for the
corresponding substituted ones. The substitutions under study comprehend
perhalogenation as other possibilities (e.g. TIPS group or sulfur substitution) which have all an
experimental counterpart. Possible consequences
of our findings on the above mentioned electronic and optical properties with respect to
applications and fundamental research will be discussed
Optical and electronic properties of monomers of eumelanin: A DFT and TD-DFT computational study
Full text linkWe report a systematic investigation on the electronic and optical properties of four monomers which are elementary constituents of some of the protomolecules of eumelanin. Eumelanin is the most important form of melanin which is one of the most universal natural pigments in living organisms. For the isolated monomers we performed all-electrons Density Functional Theory (DFT) and Time Dependent DFT (TDDFT) calculations with a localized Gaussian basis-set. For each mo-nomer we determined a series of molecular properties, namely electron affinities, ionization energies, fundamental energy-gaps, optical absorption spectra, and exciton binding energies. We discuss moreover the possible implications of the above electronic and optical properties of the single monomers with respect to the properties of a recently proposed tetrameric protomolecule of eumelanin
Effects of TIPS-Functionalization and Perhalogenation on the Electronic, Optical, and Transport Properties of Angular and Compact Dibenzochrysene
No full textWe report a systematic comparative study on dibenzo-
[b,def]chrysene (angular) and dibenzo[def,mno] chrysene (compact)
polyaromatic hydrocarbons and their bis-triisopropylsilylethynyl
(TIPS)-functionalized and perhalogenated (F, Cl) counterparts. We used
density functional theory (DFT) and time-dependent DFT to quantify the
effects of morphology and chemical modifications on the electronic, optical,
and transport properties. In particular, we compared electron affinity, ionization
energy, fundamental gap, optical absorption, exciton binding energy, and
reorganization energies for holes and electrons. For both TIPS-functionaliza-
tion and halogen substitutions, we found larger electron affinities (nearly
tripled with perchlorination). Ionization energies are found to be reduced for
TIPS-functionalization (by ∼5%) and enhanced following halogen substitution
(up to 17%). In both compact and angular dibenzochrysenes, the above trends
reflect in a general reduction of the fundamental gap (up to 22%) following
chemical modification. The effect of perhalogenation and TIPS-functionalization is always to increase molecular reorganization energies
for both holes and electrons. Concerning the optical properties, we observe a redshift of the optical onset in all cases; for
TIPS-functionalized molecules, in particular, we additionally found a remarkable enhancement of the absorption in the visible region
Computational investigation on the effect of halogen substitution on the electronic, optical, and transport properties of guanine
No full textWe present a computational investigation on the effect of halogen substitution on the electronic, optical, and transport properties of the nucleobase guanine.
We performed all-electrons Density Functional Theory and Time-Dependent Density Functional Theory calculations with a localized Gaussian basis-set and the hybrid exchangecorrelation
functional B3LYP. Results obtained with the above level of theory are in good agreement with the available experimental data for the unsubstituted molecule. We
report and discuss the effect of functional substitution on several physico-chemical properties such as: electron affinities, ionization energies, fundamental energy-gap, optical
absorption, exciton binding energy and molecular reorganization energies for holes and electrons
Computational investigation of the effects of perfluorination on the charge-transport properties of polyaromatic hydrocarbons
No full textWe present a systematic computational study of the effects of perfluorination on the charge-transport properties of three homologous classes of polyaromatic hydrocarbons of interest for molecular electronics: acenes, pyrenes, and circumacenes. By means of Density Functional Theory calculations we first obtained the key molecular properties for transport of both holes and electrons. We then used these parameters in the framework of Marcus theory to compare charge-transfer rates in the high temperatures regime for both unsubstituted and perfluorinated molecules. We additionally estimated the relative charge-mobility of each unsubstituted (perfluorinated) molecule with respect to unsubstituted (perfluorinated) pentacene. We found in all cases that perfluorination reduces the charge-transfer rate in absolute terms. This is largely due to the higher values of the molecular reorganization energies predicted for perfluorinated compounds. Interestingly, however, the charge-transfer rates for both holes and electrons of perfluorinated species are remarkably similar, especially for the larger species. In addition, in the case of the larger circumacenes the charge-mobility values relative to pentacene values are found to increase upon perfluorination
Electronic and optical properties of chromophores from bacterial cellulose
No full textWe report a systematic computational investigation on the electronic and optical properties of the principal chromophores found in bacterial cellulose (BC). In particular, we focus on the three chromophoric leading structures that were isolated from aged BC (1) 2,5-dihydroxy-[1,4]benzoquinone (2) 5,8-dihydroxy-[1,4]naphthoquinone and (3) 2,5-dihydroxyacetophenone. For the isolated molecules we performed all-electrons density functional theory (DFT) and time dependent DFT calculations with a localized Gaussian basis set and the hybrid exchange correlation functional B3LYP. We quantified key molecular properties relevant as electron affinities, ionization energies, quasi-particle energy gaps, optical absorption spectra, and exciton binding energies. We address moreover the impact of the solvent on the optical properties of the above systems using starting configurations obtained after classical molecular dynamics simulations in water. Our results could be of importance to comprehend the mechanisms underlying the processes of degradation of BC, which are of fundamental relevance for cultural heritage applications
Neutral-cluster implantation in polymers by computer experiments
No full textIn this work, we perform atomistic model potential molecular dynamics simulations by means of state-of-the art force-fields to study the implantation of a single Au nanocluster on a polydimethylsiloxane substrate. All the simulations have been performed on realistic substrate models containing up to ∼4.6 × 106 of atoms having depths up to ∼90 nm and lateral dimensions up to ∼25 nm. We consider both entangled-melt and cross-linked polydimethylsiloxane amorphous structures. We show that even a single cluster impact on the polydimethylsiloxane substrate remarkably changes the polymer local temperature and pressure. Moreover, we observe the presence of craters created on the polymer surface having lateral dimensions comparable to the cluster radius and depths strongly dependent on the implantation energy. Present simulations suggest that the substrate morphology is largely affected by the cluster impact and that most-likely such modifications favour the penetration of the next impinging clusters
Eumelanin Adsorption on Silicon: Optical Properties of Si(001)-Adsorbed Eumelanin Tetrameric Protomolecules
Full text linkWe predict the optical properties (in particular optical absorbance and reflectance anisotropy spectra (RAS)) of the silicon(001) surface organically functionalized by the adsorption of chosen tetrameric eumelanin protomolecules. These Si(001):tetramer systems can be considered as models of hybrid (porous) silicon-eumelanin interfaces, a system with potential applications in photovoltaics. In spite of a weak effect of tetramer adsorption on Si(001) overall absorption spectra, first-principles results based on plane wave density functional theory allowed us to identify specific regions, in the interesting IR and visible range, where the adsorbed molecules yield large enhancements in surface absorbance, and the appearance of new RAS features
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