Jarem Raul Garcia

Synthesis and Characterization of a New Semiconductor Oligomer Having Quinoline and Fluorene Units

A new oligomer having fluorenylene and quinolinylene groups was straightforwardly synthesized by Suzuki reaction and proven to be readily soluble in common organic solvents. The chemical structure of the copolymer was confirmed and characterized by 1H nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and gel permeation chromatography (GPC) measurements. In solution, the oligomer presented two absorption maxima at 314 and 245 nm, along with a high fluorescence quantum yield (82%), characterized by an emission maximum at 419 nm. The band gap of the material was estimated to be around 2.60 eV by cyclic voltammetry, however the optical band gap for the thin film observed by UV-Vis spectroscopy was 3.10 eV. The divergence was attributed to charge transfer interactions due to the presence of donor and acceptor units in the copolymer.

Electrochemical characterization of Langmuir–Blodgett films from the ruthenium complex mer-[RuCl3(dppb)(4-Mepy)]

Abstract Ruthenium complexes containing diphenylphosphine ligands serve as good catalysts in hydrogenation reactions, and may be used as precursors for other Ru complexes. Their properties may also be exploited in Langmuir–Blodgett (LB) films, which is the focus of the present paper. We report on electrochemical properties of LB films from the pure ruthenium (III) complex, mer -[RuCl 3 (dppb)(4-Mepy)] (dppb=PPh 2 (CH 2 ) 4 PPh 2 ; 4-Mepy=4-methylpyridine) (Ru–Pic), and from mixtures of stearic acid (SA) and Ru–Pic. Y-type LB films from these materials were deposited on indium tin oxide (ITO) substrates and analyzed using cyclic voltammetry. The overall shape of the voltammogram was the same for LB films of pure Ru–Pic and mixed with SA, with the redox peaks being ascribed to the Ru III/II conversion. However, in the mixed film, the potentials for the cathodic and anodic peaks were shifted toward more anodic and cathodic potentials, respectively, and this is attributed to the presence of SA within the coordination sphere of Ru, consistent with Fourier-transform infrared spectroscopy (FTIR) measurements. Even though Ru–Pic films at the air/water interface are not true monolayers, LB films from pure Ru–Pic display higher electroactivity than the mixed films, owing to the absence of the insulating stearic acid matrix and to the greater roughness of the pure films.

Electrochemical synthesis of the copolymer poly(2-methoxy-5-bromo-p-phenylenevinylene)/(2,5-dicyano-p-phenylenevinylene) (MB-PPV/DCN-PPV): tuning properties

The present work describes an electrochemical method to produce the copolymer poly(2-methoxy-5-bromo-p-phenylenevinylene)/(2,5-dicyano-p-phenylenevinylene) (cop-MB-PPV/DCN-PPV). This copolymer was proposed due to its D-A characteristic produced by the presence of the electron-donating methoxy moiety and the electron-withdrawing dicyano moiety. The copolymer was electrochemically synthetized by cathodic reduction of the convenient starting materials dissolved in a DMF/LiClO4 using a mercury pool acting as working electrode. The copolymer was characterized by infrared (IR), UV-Vis and fluorescence (FL) spectroscopy and cyclic voltammetry (CV). All the results were compared to the MB-PPV homopolymer. The analysis of electrochemical measurements and IR indicated that the cop-MB-PPV/DCN-PPV was obtained through the formation of blocks containing DCN-PPV units linked by blocks containing MB-PPV units. The electronic structure, performed by CV, UV-Vis and FL showed that the conduction band is more stabilized in the copolymer than in homopolymer. Furthermore, the FL spectra indicated that the light emission of the cop-MB-PPV/DCN-PPV in chloroform solution occurs by means of excimer formation.

Synthesis and Characterization of PPV Monomer for Subsequent Electropolymerization

Organic synthesis of the monomer of poly(p-phenylenevinylene) was performed starting by the 2,5-dimethylphenol compound. An iodine atom was added to one end of the aromatic ring and then the iodine atom was substituted by a cyano group. Opposite to the cyano group was added a chain of six carbon atoms and the end of the carbon chain has an added bromine atom. The characterizations of the obtained compounds were made by FTIR, GC-MS, 1H, and 13C NMR and showed that almost all of the proposed monomers were obtained in their totality.

Montmorillonite Silver Nanoparticles for Applications in Polymeric Materials

This work presents the preparation of silver nanoparticles (AgNPs) with montmorillonite to produce a nanomaterial with bactericidal properties. The modified montmorillonite was characterized through the techniques of Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray diffraction (XRD). The FTIR and Raman spectrum’s showed specific bands of involving stretching silver. In the XRD analyses was observed the occurrence of the following crystallographic planes (111), (200) e (220) silver related. The nanocomposites of polyethylene with AgNPs did not show loss in mechanical properties, this fact was important and indicate that the nanomaterial can be inserted in this polymer matrix with considerable technological interest.

SÍNTESE E CARACTERIZAÇÃO DE NANOPARTÍCULAS DE PRATA NO POLIELETRÓLITO CLORETO DE 3-N-PROPILPIRIDÍNIO SILSESQUIOXANO PARA APLICAÇÃO EM MATERIAIS TÊXTEIS DOI: 10.5212/Publ.Exatas.v.18i1.0005

No presente trabalho foi realizada a sintese e a caracterizacao das nanoparticulas de prata (AgNps), utilizando-se o polieletrolito cloreto de 3-n-propilpiridinio silsesquioxano (SiPy+Cl-) como nanoreator e a aplicacao dessas nanoparticulas para incorporacao em materiais texteis. As sinteses das AgNps foram realizadas pelo metodo de precipitacao, utilizando-se o AgNO3 como precursor, o polieletrolito (SiPy+Cl-) como estabilizante e o NaBH4 como agente redutor. A sintese foi realizada em quatro proporcoes (1%, 2%, 5% e 10% m/V de prata em relacao ao polieletrolito) e a formacao, estabilidade e tamanho das nanoparticulas foram analisadas por espectroscopia de UV-Vis e Potencial Zeta. Observou-se que na presenca do SiPy+Cl-, a banda plasmonica das AgNps, na regiao de 350- 450 nm, apresentou-se deslocada para maiores comprimentos de onda, o que pode estar associado a interacao do SiPy+Cl- com as AgNps ou a diferenca de tamanho das nanoparticulas estabilizadas em relacao as AgNps livres. As nanoparticulas obtidas nas proporcoes 5% e 10% m/V apresentaram-se mais estaveis, com tamanhos medios de aproximadamente 25 a 45 nm. A partir dos espectros de infravermelho com transformada de Fourier (FTIR), pode-se constatar um decrescimo na intensidade das bandas em 1634 e 1484 cm-1 referente as vibracoes do anel piridinio apos a incorporacao das AgNps, evidenciando interacoes entre eles. O tamanho medio dos cristalitos, calculado pela equacao de Scherer, foi de 42 nm e 48 nm para as amostras com 10% e 5% de prata, respectivamente. A atividade antimicrobiana das AgNps impregnadas em tecidos de algodao foi avaliada e apresentou resultados promissores na inibicao do crescimento bacteriano e fungico.