Jordan Del Nero

Spectroscopic study of polyazopyrroles (a narrow band gap system)

Abstract Polyazopyrroles are systems that are derived from the dipyrroles by inserting an azo group among the pyrroles rings. This new polymer present a significant decrease in energy gap lowering from 2.5 eV to 1.0 eV. In this work we present a theoretical absorption spectrum obtained by the ZINDQ/S method using the geometries optimized from the AM1 and PM3 semiempirical methods. As there are experimental evidences that this system presents polaron defects, we also include the effect of the polaron type defects on the electronic structure. The results are in good agreement with the experimental ones.

Electronic structure of dithienopyrrole, dithienothiophene and thionaphtheneindole

Dithienopyrrole (DP), Dithienothiophene (DT) and Thionaphtheneindole (TNI) are electrochromic semiconductor polymers that possess very similar electronic structure. These materials were synthesized in the middle of the nineties with the intention to obtain an improvement in the processability of the electrochromic polymers and investigate the mechanism of charge transport in the polymeric net. In this work, we investigated the electronic, conformational and spectroscopic structure of oligomers formed by the mentioned systems. Density of states and wavefunction were calculated to study the conduction mechanism in the net of these polymers through polaron defect type. We used the semiempirical methods for calculations of electronic structure of the polymers and copolymers coupled with ZINDO/Spectroscopic method to simulate the behavior of absorption for neutral and charge systems. We adopted EHT description for the conformational defects and we investigated the electrical conduction as a function of defects concentration.

Optical spectroscopy of heterocycles based on pyrrole, furan and thiophene

Abstract Recently Joshi et al synthesised a serie of nine triheterocycles based on pirrole, furan and thiophene. All the systems were chemically polymerised and oxidised with NOPF6. The experimental results indicated the presence of polarons in three of the systems that cause appreciable electrical conductivity values. In this work we present a theoretical spectroscopy study for oligomers builded with these materials. In our calculations we utilised the semi empirical AM1 method for the geometric simulation of the oligomers. Optical absorption spectra for neutral and charged systems were done by using ZINDO/S method.

Polycarbonitrile : A semiempirical, ab initio and density functional study of molecular stability

Abstract The theoretical literature data with respect to the electronic properties of this compound is quite scarce and makes use of the planar all-trans structure as the most stable for the calculations. In this work semiempirical (AM1 and PM3), ab initio (at the Hartree-Fock level) and density functional theory (using the correlation functional of Vosko, Wilk and Nussair) were used to analyse the conformational stability of the all-trans and all-cis dimers, trimers and tetramers of polycarbonitrile. The semiempirical and ab initio calculations at the Hartree-Fock level showed in general that the all-trans structure with respect to other conformers is the most unstable structure. The inclusion of electronic correlation energy through the MP2 calculations or the VWN functional method suggest that the trans structure is the most stable. The relative energies calculated at the correlated level presented differences around 2 kcal/mol among the different conformers. While the all-cis compounds presented a planar structure for any of the three methods, the all-trans polymer showed a strong deviation of planarity with a set of local minima in its energy surface. These results suggest that further calculations on the electronic properties of this polymer can be significantly different of those actually available in the literature.

Proposal for a single-molecule field-effect transistor for phonons

We propose a practical realization of a field-effect transistor for phonons. Our device is based on a single ionic polymeric molecule and it gives modulations as large as -25% in the thermal conductance for feasible temperatures and electric field magnitudes. Such effect can be achieved by reversibly switching the acoustic torsion mode into an optical mode through the coupling of an applied electric field to the dipole moments of the monomers. This device can pave the way to the future development of phononics at the nanoscale or molecular scale.

A comparative study of ordered and disordered distribution of defects in polyazine derivatives

In this work we report the electronic structure of polyazine derivatives, in the presence of conformational defects like bipolaron. The Negative Factor Counting technique and the Inverse Iteraction Method were used to find the electronic density of states and the wavefunctions, respectively. Our results show a red shift at the Fermi energy for high concentration defect in disordered systems and in ordered systems we have localized wavefunctions. Together with the extention of the highest occupied molecular orbital (HOMO) state, this indicates the possibility to have the polymer in the metallic regime.

Effect of bipolaron type of defect on the polyacetylenepolycarbonitrile copolymer

In the present work we report a theoretical study on the effect of the presence of conformational defects like bipolaron on the electronic properties of polyacetylene-polycarbonitrile copolymers. Negative Factor Counting and inverse iteraction techniques have been used to evaluate densities of states and wave functions, respectively. Our results show a finite density of state at the Fermi energy for high concentration defect. This fact, together with the extention of the highest occupied molecular orbital (HOMO) state, indicate the possibility to have the copolymer in the metallic regime.

Study of copolymer composed by polyacetylene and polyazine

Abstract The polyacetylene was investigated by us showing the presence of conductive states in the Fermi level caused by a disordered distribution of defects of soliton type. Also we have shown that the polyazine polymer presents conductive characteristics through defects of the bipolaron type for orderly and disordered systems. The aim of this investigation is to verify whether the copolymer from polyacetylene and polyazine can be found on the metallic regime. For the calculations of this system we used semiempirical methods for the optimization of the geometry.Our results indicate that, when we take of charge from the structure, the bipolaron type of defect is formed on the copolymer.

ELECTRONIC STRUCTURE OF POLYCARBONITRILE : THE ROLE OF POLARON-TYPE DEFECTS

Abstract In this work we report the electronic structure of polycarbonitrile, a conjugate polymer generated from polyacetylene by replacing every second CH unit by a single N atom, in the presence of defects like polarons. The negative factor counting method was used in a tight-binding parameterization and geometrical data were from Austin model 1 (AM1) calculations. A comparative study of the ordered and disordered distribution of defects is presented.

Dye incorporation in polyphosphate gels: synthesis and theoretical calculations

In this work we described theoretical calculations on the electronic structure and optical properties of the dyes crystal violet and malachite green based in semiempirical methods (Parametric Method 3 and Intermediate Neglect of Differential Overlap / Spectroscopic - Configuration Interaction) and the synthesis of a new hybrid material based upon the incorporation of these dyes in an aluminum polyphosphate gel network. The samples are nearly transparent, free-standing thick films. The optical properties of the entrapped dyes are sensitive to chemical changes within the matrix caused either by gel aging or external stimulli such as exposition to acidic and basic vapors that can percolate within the matrix. Our theoretical modeling is in good agreement with the experimental results for the dyes.