Interações de complexos metálicos com nanotubos de carbono: um estudo teórico

Abstract

In this work, quantum mechanical methods were applied to investigate the structural and nonlinear optical (NLO) properties of porphyrin (P) and tetraphenylporphyrin (TFP) molecules, as well as hybrid systems formed by different porphyrin derivatives (ZnP, H2P, ZnP-pp and H2P-pp) adsorbed on the surface of a single-walled carbon nanotube (SWNT) a(5,5). The molecular geometries were calculated using Density Functional Theory (DFT) and the first hyperpolarizability was calculated at the Hartree-Fock (HF) level. Firstly, the structural aspects of sixty four porphyrin and tetraphenylporphyrin molecules complexed with Zn (II) (ZnP and ZnTFP) or in the protonated form (H2P and H2TFP), modified by substituents bound directly to the macrociclotetrapirrólico ring were evaluated. The smallest distortions of the porphyrin and tetraphenylporphyrin ring were found when the bridge group was the ethynyl radical (et) conecting the electron donor and acceptor groups, NH2 and NO2, respectively. The average first hyperpolarizability for these molecules was calculated and β values were larger for porphyrins and tetraphenylporphyrin containing push-pull ligands type, especially those that contain in their structures the ethynyl linker. The second part of this work involved the study of structure, stability and NLO property of a series of porphyrin-nanotube complex (ZnP-SWNT, H2P-SWNT, ZnP-pp-SWNT and H2P -pp-SWNT). The results indicated that the stability of the complexes is directly related to the presence of Zn(II) ion, in addition, the push-pull groups also contribute to the overall stability. By taking the average stabilization energy throughout the series of isomers, the following stability order was established: ZnP-pp-SWNT>ZnPSWNT~H2P-pp-SWNT>H2P-SWNT. The carbon nanotubes functionalization with porphyrins enhance the ONL response. The β values increase significantly when the SWNT is functionalized with the H2P-pp and ZnP-pp molecules if compared to the free porphyrins. The results obtained in this work indicate that hybrid nanocomposites, such as those represented by H2P-pp-SWNT and ZnP-pp-SWNT, might be an important alternative to the proposition of interesting new materials with ONL responses.