Oscar Baldovino-Pantaleón

Third-order nonlinear optical properties of colloidal Au nanorods systems: saturable and reverse-saturable absorption

In this work, we present a study of the nonlinear absorption properties from different gold nanorod (NR) systems in aqueous suspension. The NRs were obtained with the bottom-up protocol by the seed-mediated growth method (SMG), using Ag(+) ions at different concentrations, and CTAB as surfactant. By using this method, aspect ratios between 2 and 5 were obtained. The transverse surface plasmons (TSP) are located between 514 - 535 nm, while the longitudinal surface plasmons (LSP) are between 639 - 921 nm, for the different samples studied. The Z-scan technique was implemented for open (OA) and closed (CA) aperture at 532 and 1064 nm, with laser pulses of 26 ps, for vertical and horizontal polarizations, with respect to the incidence plane (horizontal). At 532 nm all samples showed saturable absorption (SA), while for samples with LSP near 1064 nm, such effect was observed only at low-energy pulse experimental conditions. In the high-energy pulse regime, an apparent reverse-saturable absorption (RSA) was observed for both wavelengths. However for 532 nm, it was possible to determine that this effect results from structural changes in the samples, which are manifested through the behavior of nonlinear absorption and refraction curves. These results were used to determine the irradiances to which NRs can be modified by photodegradation.

Gasohol Quality Control for Real Time Applications by Means of a Multimode Interference Fiber Sensor

In this work we demonstrate efficient quality control of a variety of gasoline and ethanol (gasohol) blends using a multimode interference (MMI) fiber sensor. The operational principle relies on the fact that the addition of ethanol to the gasohol blend reduces the refractive index (RI) of the gasoline. Since MMI sensors are capable of detecting small RI changes, the ethanol content of the gasohol blend is easily determined by tracking the MMI peak wavelength response. Gasohol blends with ethanol contents ranging from 0% to 50% has been clearly identified using this device, which provides a linear response with a maximum sensitivity of 0.270 nm/% EtOH. The sensor can also distinguish when water incorporated in the blend has exceeded the maximum volume tolerated by the gasohol blend, which is responsible for phase separation of the ethanol and gasoline and could cause serious engine failures. Since the MMI sensor is straightforward to fabricate and does not require any special coating it is a cost effective solution for real time and in-situ monitoring of the quality of gasohol blends.

Unusual nucleophilic versus electrophilic aromatic substitution on nitroanilines

Abstract The reaction of the regioisomeric nitroanilines with KI and HNO 3 /bentonite system using microwave energy in solvent-free conditions is reported. In accordance with the obtained results, an unusual competence between nucleophilic aromatic substitution versus electrophilic aromatic substitution was detected. With the para isomer two products were obtained, one for each reaction type; however, with the meta -nitroaniline, only the nucleophilic substitution product was detected, and finally with the ortho isomer in addition to the nucleophilic and electrophilic substitution products, we detected the formation of 2,4-diiodonitrobenzene. In order to explain the achieved products, we propose that the last product is formed in two steps: firstly by a nucleophilic aromatic substitution, and secondly by an electrophilic aromatic substitution.

A second monoclinic polymorph of {2,6-bis[(2,4,5-trifluoro­phen­yl)imino­meth­yl]pyridine-κ3N,N′,N′′}dichloridonickel(II)

The asymmetric unit of the title compound, [NiCl2(C19H9F6N3)], contains one half-molecule residing on a crystallographic twofold rotation axis. The title compound crystallizes in space group C2/c while the previously reported polymorph was reported in P21/c [Baldovino-Pantaleón et al. (2006 ▶). Adv. Synth. Catal. 348, 236–242]. The Ni2+ ion exhibits a pentacoordinate distorted trigonal–bipyramidal NiCl2N3 geometry, with two Cl atoms in the equatorial plane. In the crystal, molecules are linked by intermolecular C—F⋯π [F⋯centroid = 2.9676 (14) Å] interactions.

Novel synthesis of new 1,2,4‐trithioles by reductive coupling of benzoyldithioacetic acid derivatives mediated by Sml2

1,2,4-trithioles 2a–e are readily obtained in good yields by dimerization of benzoyldithioacetic acid derivatives using samarium diiodide as a promotor under very mild conditions. The structures of compounds 2a–e were determined by IR, 1H, and 13C NMR spectroscopies using heteronuclear multiple bond correlation, heteronuclear multiple quantum correlation, and nuclear Overhauser enhancement spectroscopy experiments, mass spectrometry, and, in the case of 2a, the structure was confirmed by single-crystal X-ray diffraction studies.

Nonlinear Optical Properties of Au Colloidal Nanorod Systems

Colloidal Au nanorods systems obtained by SMG were studied. Their third order nonlinear response was studied using the z-scan technique at 532 nm and 1064 nm with 26 ps pulses for high and low irradiances.

Linear and Nonlinear Optical Properties of Au Colloidal Nanorod Systems

Colloidal Au nanorods systems obtained by SMG were studied. An average negligible birefringence was measured in the 450-950nm region. Their third order nonlinear response was studied using the z-scan technique at 532nm with 26ps pulses.