Luz María Rodríguez-Valdez

Theoretical study of electronic properties of organic photovoltaic materials

It has been proved that fullerene derivatives, in which an oligophenylenevinylene (OPV) group is attached to C60, present an interesting photophysical phenomenon and can be incorporated into photovoltaic cells. In these systems, the OPV acts as electron donor upon excitation, and then fullerene absorbs photoexcited electrons. These new organic semiconductor materials offer the prospect of lower manufacturing costs and they present several advantages: easy fabrication, large area, flexible and light weight devices when compared with inorganic counter parts. In the present theoretical study, oligomeric chains of p‐phenylenevinylene (n‐PPV, n = 3–8 units) and C60‐OPV hybrids have been studied by density functional theory (DFT). Electronic properties such as electronic absorption and emission spectra were calculated in order to determinate how the increment of spectroscopic units affects their electronic behavior. These properties were carried out with time dependent‐density functional theory (TD‐DFT) and ZINDO semiempirical method. The theoretical calculations of the structural properties of n‐PPV and fullerene‐OPV hybrids were obtained using PBE1PBE/6‐31G and ONIOM two‐layered version, respectively. All calculations were done with Gaussian 03W program package.

Experimental and quantum chemical studies of a novel synthetic prenylated chalcone

BackgroundChalcones are ubiquitous natural compounds with a wide variety of reported biological activities, including antitumoral, antiviral and antimicrobial effects. Furthermore, chalcones are being studied for its potential use in organic electroluminescent devices; therefore the description of their spectroscopic properties is important to elucidate the structure of these molecules. One of the main techniques available for structure elucidation is the use of Nuclear Magnetic Resonance Spectroscopy (NMR). Accordingly, the prediction of the NMR spectra in this kind of molecules is necessary to gather information about the influence of substituents on their spectra.ResultsA novel substituted chalcone has been synthetized. In order to identify the functional groups present in the new synthesized compound and confirm its chemical structure, experimental and theoretical 1H-NMR and 13C-NMR spectra were analyzed. The theoretical molecular structure and NMR spectra were calculated at both the Hartree-Fock and Density Functional (meta: TPSS; hybrid: B3LYP and PBE1PBE; hybrid meta GGA: M05-2X and M06-2X) levels of theory in combination with a 6-311++G(d,p) basis set. The structural parameters showed that the best method for geometry optimization was DFT:M06-2X/6-311++G(d,p), whereas the calculated bond angles and bond distances match experimental values of similar chalcone derivatives. The NMR calculations were carried out using the Gauge-Independent Atomic Orbital (GIAO) formalism in a DFT:M06-2X/6-311++G(d,p) optimized geometry.ConclusionConsidering all HF and DFT methods with GIAO calculations, TPSS and PBE1PBE were the most accurate methods used for calculation of 1H-NMR and 13C-NMR chemical shifts, which was almost similar to the B3LYP functional, followed in order by HF, M05-2X and M06-2X methods. All calculations were done using the Gaussian 09 software package. Theoretical calculations can be used to predict and confirm the structure of substituted chalcones with good correlation with the experimental data.

Surface plasmon resonances in Drude metal cylinders: radius dependence and quality factor

We have studied the dispersion relation of surface plasmon modes in metal cylinders using the Drude model by numerically solving complex eigenfrequencies as a function of the radius. We also studied the quality factor Q of the modes and found that it decays as the radius is increased, and for a small radius there is a maximum value equal to independent of the mode order (where is the Ritchie’s surface plasmon frequency and γ is the damping constant).

Synthesis of exo-Imidazolidin-2-one Dienes, Their Isomerization, and Selectivity in Diels–Alder Cycloadditions

An efficient and alternative synthesis of exo-imidazolidin-2-one dienes is described. A condensation reaction was carried out with bis-imino derivatives, diacetyl, and triphosgene, affording symmetrically N, N-disubstituted dienes. The use of alkyl methyl α-diketones led to the formation of nonsymmetrical dienes, which underwent isomerization to provide more stable inner-outer-ring dienes under Lewis acid conditions. Evaluation was made of the reactivity as well as regio- and stereoselectivity of these dienes in Diels-Alder reactions. They proved to be highly reactive and selective. DFT calculations of the transition states accounted for their behavior.

Theoretical and experimental analysis of porphyrin derivatives with suitable anchoring groups for DSSC applications

In this contribution, different porphyrin derivatives were experimentally synthesized and theoretically analyzed using several electronic structure methods to study the geometrical and electronic properties of A4, trans-A2B2and A3B porphyrins bearing several functional groups (–OH, –COOH, -3,5-di-tBu, –OCH2CH2CH2COOEt and –OMe) suitable to be employed as dyes in Dye Sensitized Solar Cells (DSSC). A4 (R = -H, -OMe, -OH, -3,5-di-tert-butyl, –OCH2CH2CH2COOEt) and A3B (R1=R2=R3=–H; R4=–OH and R4=-3,5-di-tBu) porphyrins were synthesized and characterized by UV-vis and 1H NMR spectroscopies for comparison. The geometrical parameters were analyzed in the ground state and gas phase using the semiempirical method PM6 and the DFT functionals M06-2X and B3LYP, in combination with the 6-31G(d), DZVP and TZVP basis set. For calculations of the electronic and excited state properties, CAM-B3LYP, M06-2X and HSE06, using SMD as solvation model, were applied. This study revealed that HSE06/DZVP protocol is the best method...