RESUMO
The noncovalent dyad of tetraphenylporphine and C60 fullerene (H2TPP···C60) and the tetraphenylporphine dimer (H2TPP···H2TPP) were studied by density functional theory (DFT), using functionals that incorporate empirical dispersion correction (DFT-D), functionals that use a long-range correction (LC) scheme, a hybrid functional (B3LYP) and a highly parametrized empirical exchange-correlation functional (M05-2X). The results were compared to X-ray structures and interaction energies reported in previous experimental and theoretical studies. It was found that B3LYP and CAM-B3LYP functionals fail to reproduce the X-ray structures and binding energies of the TPP···C60 system. DFT-D functionals overestimated the π···π energy interactions for both systems, however, the optimized structures agree well with those observed experimentally. The LC-BLYP functional predicts geometries similar to X-ray structures; nevertheless, due to the lack of correction in the dispersion energy, the predicted energies for both model systems are low. On the other hand, the M05-2X functional exhibited the best performance. Both the structures and binding energies calculated with M05-2X are consistent with experimental and theoretical evidence reported by other authors, as well as with our experimental results obtained by means of atomic force microscopy on H2TPP thin films grown on the HOPG/C60 substrate by physical vapor deposition.
RESUMO
Dendrimers bearing pyrene donor groups have been obtained and act as efficient light-harvesting antennae capable of transferring light energy through space from their periphery to their core. The light-harvesting ability increases with each generation due to an increase in the number of peripheral pyrenes. In order to evaluate the photovoltaic properties of the compounds, thermal evaporated thin films were produced and the voltage response in the presence of visible light was obtained. The energy transfer efficiency was found to be almost quantitative for the first and second generations. The dendrimers have the potential to become integral components of molecular photonic devices.
Assuntos
Dendrímeros/síntese química , Porfirinas/química , Pirenos/química , Dendrímeros/química , Eletroquímica , Transferência de Energia , Complexos de Proteínas Captadores de Luz , Estrutura MolecularRESUMO
We performed density functional theory (DFT) calculations of noncovalently bonded 1:1 complex of meso-tetraphenylporphine H2TPP with fullerene C60. The functionals used were PW91, PBE and BLYP of general gradient approximation (GGA), as well as PWC and VWN of local density approximation (LDA) as implemented in the DMol3 module of Materials Studio package from Accelrys. The computed geometries were compared to the experimental X-ray diffraction data obtained elsewhere for rhombohedral and monoclinic H2TPP + C60 crystalline complexes. If the correlation coefficient between the calculated and experimental data is applied, the covalent bond lengths and angles within H2TPP unit are best reproduced by BLYP functional, whereas PWC and VWN are least precise. On the other hand, PWC and VWN are the best functionals in reproducing the separations between H2TPP and C60 found from X-ray diffraction analysis: the LDA-calculated N(H2TPP) ... C(C60) distances are of about 2.9-3.0 angstroms, whereas the corresponding experimental values are of ca. 3.0-3.1 angstroms. Next are PW91 and PBE functionals, giving N(H2TPP) ... C(C60) distances of ca. 3.5-3.6 angstroms. BLYP produced the separations of around 4.0-4.1 angstroms, which are inconsistent with both X-ray data and the results produced other functionals. We also analyzed functional-dependent variations in formation energies, electrostatic potential, HOMO, LUMO and charge transfer. We concluded that of DFT functionals incorporated into DMol3 module and tested in this study, PWC and VWN are the most adequate ones, and BLYP is the least recommended one for the studies of noncovalent interactions of porphyrins with carbon nanoclusters.
Assuntos
Fulerenos/química , Porfirinas/química , Fenômenos Químicos , Modelos Moleculares , Difração de Raios XRESUMO
We report on the preparation of fullerene C60 thin films chemically cross-linked with octane-1,8-dithiol, which are capable of binding gold nanoparticles. The formation of a polymer was directly proved by means of laser desorption/ionization time-of-flight mass spectra, in which we observed the cleavage of fullerene-dithiol polymer at different bonds. Fourier-transform infrared, Raman and UV-visible spectra of the functionalized films exhibited notorious changes due to the formation of new covalent bonds between C60 molecules and bifunctional thiol. We further demonstrated that the dithiol-functionalized fullerene can be employed as a support for stable and homogeneous deposition of gold nanoparticles. Their average size is about 5 nm according to high-resolution transmission electron microscopy observations, and up to 20 nm, as found from scanning tunneling microscopy images. The proposed binding mechanism is through a strong coordination attachment between Au nanoclusters and sulfur donor atoms of the functionalized fullerene, as supported by density functional theory calculations.