Wagner M. Faustino

Design of ligands to obtain lanthanide ion complexes displaying high quantum efficiencies of luminescence using the sparkle model

Abstract In this paper we exemplify how to use our sparkle model for the calculation of lanthanide complexes (SMLC-AM1-INDO/S-CI) together with Fermis golden rule with the multipolar and exchange mechanisms to describe the ligand–lanthanide ion energy transfer for the purpose of designing ligands to obtain complexes displaying high quantum efficiencies of luminescence. Accordingly, we propose aromatic imides as efficient antennas and energy transfer ligands when coordinated to Eu3+ ion. More specifically we designed Eu(btfai)3bipy (btfai=benzoyltrifluoroacetylimide anion and bipy=bipyridine) and Eu(bzaci)3bipy (bzaci=benzoylacetylimide anion) which we then compare with their β-diketone analogues Eu(btfa)3bipy (btfa=benzoyltrifluoroacetonate) and Eu(bzac)3bipy (bzac=benzoylacetonate), which have been previously synthesized and whose quantum efficiencies we have also previously measured. Our theoretical results indicate that indeed the quantum efficiencies of Eu(btfai)3bipy and Eu(bzaci)3bipy are electronically equivalent to their highly luminescent β-diketone analogues with the advantage of one less hydrogen directly bonded to the central atom of the β-dicarbonylic anionic species. Indeed the possibility of vibronic coupling through that bond vibrational mode, which may be partially quenching the luminescence from the 5D0 level of the Eu3+ ion in the β-diketone analogues case, is thus eliminated.

TiO2@Silica nanoparticles in a random laser: Strong relationship of silica shell thickness on scattering medium properties and random laser performance

A TiO2@Silica nanoparticle has been introduced in a random laser. TiO2 particles with an average diameter of 0.41 μm were coated with silica shells of different thicknesses. Strong dependency of silica shell thickness on the medium scattering strength was found. A mathematical relationship between the scattering mean free path, random laser threshold, and random laser efficiency was developed. Higher efficiency, lower laser threshold, narrower bandwidth, and longest photobleaching lifetime were obtained in the random laser that had increased silica shell thickness. Optical colloidal stability and light coupling enhancement with scattering particles, provided by silica shell, should lead to improved laser performance.

In vitro and in vivo documentation of quantum dots labeled Trypanosoma cruzi–Rhodnius prolixus interaction using confocal microscopy

Semiconductor quantum dots (QDs) are highly fluorescent nanocrystals markers that allow long photobleaching and do not destroy the parasites. In this paper, we used fluorescent core shell quantum dots to perform studies of live parasite-vector interaction processes without any observable effect on the vitality of parasites. These nanocrystals were synthesized in aqueous medium and physiological pH, which is very important for monitoring live cells activities, and conjugated with molecules such as lectins to label specific carbohydrates involved on the parasite-vector interaction. These QDs were successfully used for the study of in vitro and in vivo interaction of Trypanosoma cruzi and the triatomine Rhodnius prolixus. These QDs allowed us to acquire real time confocal images sequences of live T. cruzi–R. prolixus interactions for an extended period, causing no damage to the cells. By zooming to the region of interest, we have been able to acquire confocal images at the three to four frames per second rate. Our results show that QDs are physiological fluorescent markers capable to label living parasites and insect vector cells. QDs can be functionalized with lectins to specifically mark surface carbohydrates on perimicrovillar membrane of R. prolixus to follow, visualize, and understand interaction between vectors and its parasites in real-time.

Lanthanide Dithiocarbamate Complexes: Efficient Catalysts for the Cyanosilylation of Aldehydes

A new class of lanthanide dithiocarbamate complexes was used to promote the cyanosilylation of aldehydes at high yields at room temperature. This represents the first application of lanthanide dithiocarbamate acting as Lewis acid.

Comment on trivalent europium lifetimes in the presence of intramolecular energy transfer processes

This work emphasizes the importance of conceptually distinguishing between lifetimes in the absence (natural lifetimes) and in the presence of intramolecular energy transfer processes in lanthanide coordination compounds. It is focused on trivalent europium compounds with mixed ligands, and a case study is made on results recently reported in the literature.

Random Lasing at Localization Transition in a Colloidal Suspension (TiO2@Silica)

Anderson localization of light and random lasing in this critical regime is an open research frontier, which besides being a basic research topic could also lead to important applications. This article investigates the random laser action at the localization transition in a strongly disordered scattering medium composed of a colloidal suspension of core–shell nanoparticles (TiO2@Silica) in ethanol solution of Rhodamine 6G. The classical superfluorescence band of the random laser was measured separately by collecting the emission at the back of the samples, showing a linear dependence with pumping fluence without gain depletion. However, frontal collection showed saturation of the absorption and emission. Narrow peaks of approximately equal intensity are observed on top of the classical superfluorescence band, indicating suppression of the interaction between the peaks modes. The linewidth of these peaks is lower than that of the passive modes of the scattering medium. A method called fraction of absorbed pumping allowed us to infer that this peak’s mode (localized modes) is confined to a shallow region near the input-pumping border.

Eu(III) dithiocarbamate complex and N-p-tolylsulfonylphenylalanine as a novel chiral catalyst for the asymmetric synthesis of cyanohydrins

The use of a new chiral lanthanide complex derived from a europium dithiocarbamate complex and a N-tosylated amino acid for the asymmetric synthesis of cyanohydrins is described. In some cases, high enantioselectivities were observed.

Low Temperature Synthesis of Luminescent RE2O3:Eu3+ Nanomaterials Using Trimellitic Acid Precursors

[RE(TLA)·(H2O)n:Eu3+] (RE3+: Y, Gd and Lu; TLA: trimellitic acid) precursor complexes were synthesized by an one step aqueous co-precipitation method. After annealing for 1 h, RE2O3:Eu3+ nanophosphors were formed through the benzenetricarboxylate low temperature thermolysis method (500-1000 oC). The compounds were characterized by using different techniques [elemental analysis (CHN), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG/DTG), X-ray powder diffraction (XPD) and scanning electron microscope (SEM)]. The XPD data indicated that the Y2O3:Eu3+ materials have crystallite size range from 11 to 62 nm. The SEM and transmission electron microscopy (TEM) images show that the annealed materials keep morphological similarities with the precursor complexes. The photoluminescence properties were studied based on the excitation and emission spectra, and luminescence decay lifetimes of the 5D0 emitting level of the Eu3+ ion. The experimental intensity parameters (Ωλ), lifetimes (τ), as well as radiative (Arad) and non-radiative (Anrad) decay rates were calculated and discussed. The RE2O3:Eu3+ phosphors (RE: Y3+ and Lu3+) annealed at 500 to 1000 oC have emission quantum efficiency (intrinsic quantum yield) values from 60 to 82%, indicating that this material can be potentially used for optical markers applications.

Simple silanization routes of CdSe and CdTe nanocrystals for biological applications

Semiconductor colloidal quantum dots have been, for the past two decades, incorporated in a wide range of applications from catalysis and optical sensors to biolabels. For this reason, simple, cheap and reproducible routes of synthesis are the main goal of many research groups around the world. They seek the production of a very stable and extremely quantum efficient nanocrystal that can afford rough changes in the external environment. Silica capping is becoming a very common tool in the quest for a stable quantum dot, because of its strong and stable structure, this material provides a great insulator to the nanocrystal from the outside. The nanocrystal surface is not chemically favorable to the deposition of the bare silica shell, what demands a bifunctional molecule that provides the linkage between the core and the shell. In this work we present a comparison between several silanization methods of thiol capped CdSe and CdTe quantum dots, showing some simplifications of the routes and an application of the quantum dots produced as fluorescent cell markers in acquisition of confocal microscopy images.

Energy transfer processes in Tb(III)-dibenzoylmethanate complexes with phosphine oxide ligands

The Tb3+-β-diketonate complexes [Tb(DBM)3L], [Tb(DBM)2(NO3)L2] and [Tb(DBM)(NO3)2(HMPA)2] (DBM = dibenzoylmethanate; L: TPPO = triphenylphosphine oxide or HMPA = hexamethylphosphine oxide) were prepared and characterized by elemental analysis (CHN), complexometric titration with EDTA and Fourier transform infrared (FTIR) spectroscopy, and the photoluminescence properties evaluated. The triplet state energies of the coordinated DBM ligands were determined using time-resolved phosphorescence spectra of analogous Gd3+ complexes. The results show that the energies increase along with the number of coordinated nitrate anions replacing the DBM ligand in the complexes. The luminescence spectra and emission lifetime measurements revealed that the ligand-to-metal energy transfer efficiency follows the same tendency. Unlike the tris-DBM complexes, bis- and mono-DBM presented high luminescence, and may act as promising candidates for preparation of the emitting layer of light converting molecular devices (LCMDs).