Simone M. C. Gonçalves

A Comprehensive Strategy to Boost the Quantum Yield of Luminescence of Europium Complexes

Lanthanide luminescence has many important applications in anion sensing, protein recognition, nanosized phosphorescent devices, optoelectronic devices, immunoassays, etc. Luminescent europium complexes, in particular, act as light conversion molecular devices by absorbing ultraviolet (UV) light and by emitting light in the red visible spectral region. The quantum yield of luminescence is defined as the ratio of the number of photons emitted over the number of UV photons absorbed. The higher the quantum yield of luminescence, the higher the sensitivity of the application. Here we advance a conjecture that allows the design of europium complexes with higher values of quantum yields by simply increasing the diversity of good ligands coordinated to the lanthanide ion. Indeed, for the studied cases, the percent boost obtained on the quantum yield proved to be strong: of up to 81%, accompanied by faster radiative rate constants, since the emission becomes less forbidden.

General synthesis of alkyl phenyl selenides from organic halides mediated by zinc in aqueous medium

Abstract Organic halides of different structural types react with diphenyl diselenide and zinc dust in aqueous medium to give alkyl phenyl selenides. Benzylic and allylic bromides, α-bromoesters, acids and ketones and some primary alkyl iodides produce high yields even under acidic conditions. Less reactive halides need basic medium. The reaction proceeds equally well in the presence of various unprotected functional groups. Control experiments support a S H 2 mechanism via alkyl radicals.

Indium(I) bromide-mediated bromocyanomethylation of carbonyl compounds

Abstract Bromocyanomethylation of a variety of carbonyl compounds to produce the corresponding 2-bromo-3-hydroxynitriles has been achieved in moderate to good yields by the action of dibromoacetonitrile and indium(I) bromide. Moderate diastereoselectivity was observed. Exclusive mono-coupling at the carbonyl group was found with 1,2-diketones and α-haloketones.

SELECTIVE PREPARATION OF α,α-DICHLOROKETONES WITH COPPER(II) CHLORIDE

ABSTRACT Aryl and enolizable alkyl ketones react with copper(II) chloride in dimethylformamide to produce the corresponding α,α-dichloroketone in high yields. Remarkable qualities of the process are high selectivity towards these substrates, undetected polychlorinated by-products, easy work-up, commercially available reagents and HCl as the only waste stream.

Indium(I) bromide-mediated dichlorocyanomethylation of carbonyl compounds. The preparation of 2,2-dichloro-3-hydroxynitriles

Abstract Carbonyl compounds were efficiently transformed into their corresponding 2,2-dichloro-3-hydroxynitrile derivatives by the action of trichloroacetonitrile and indium(I) bromide.

Chemical Partition of the Radiative Decay Rate of Luminescence of Europium Complexes.

The spontaneous emission coefficient, Arad, a global molecular property, is one of the most important quantities related to the luminescence of complexes of lanthanide ions. In this work, by suitable algebraic transformations of the matrices involved, we introduce a partition that allows us to compute, for the first time, the individual effects of each ligand on Arad, a property of the molecule as a whole. Such a chemical partition thus opens possibilities for the comprehension of the role of each of the ligands and their interactions on the luminescence of europium coordination compounds. As an example, we applied the chemical partition to the case of repeating non-ionic ligand ternary complexes of europium(III) with DBM, TTA, and BTFA, showing that it allowed us to correctly order, in an a priori manner, the non-obvious pair combinations of non-ionic ligands that led to mixed-ligand compounds with larger values of Arad.

Enantiomeric excess detection with (S)-3-Phenyl-2-(selenophenyl)propan-1-ol derivatizing agent via mix and shake 77Se NMR

Neste artigo demonstramos que o composto (S)-3-fenil-2-(selenofenil)propan-1-ol pode ser empregado com sucesso como agente de derivatizacao quiral na determinacao de excesso enantiomerico de substratos acidos carboxilicos quirais via RMN de 77Se. Os derivados diastereomericos sao obtidos atraves da mistura do agente de derivatizacao quiral com um substrato acido nao racemico no proprio tubo de RMN e o excesso enantiomerico e determinado com apenas um espectro. Os melhores resultados foram os obtidos com o emprego do (S)-3-fenil-2-(selenofenil)propan-1-ol, que apresentou boas anisocronias para os sinais de selenio, variando entre Δδ = 22 Hz a Δδ = 211 Hz, mesmo com ate 5 ligacoes separando o estereocentro do atomo de selenio.

Synthesis of Chalcogenides using Indium Intermediates in Aqueous Media

Abstract Selenides and vinylic selenides were synthesized from their corresponding organic halides and alkynes in aqueous media using indium metal.

Substantial luminescence enhancement in ternary europium complexes by coordination of different ionic ligands

We demonstrate in a general and comprehensive manner that a substantial enhancement of luminescence in europium complexes can be achieved by increasing ionic ligand diversity. For the complexes studied, the measured boosts in the quantum efficiency of luminescence obtained using this strategy ranged from a minimum of 100% to a maximum of 543%. We formalize this concept by means of mathematical inequalities which describe the fact that either the quantum efficiency η, or the radiative decay rate Arad, of a mixed ligand complex will be larger than the average of the same property for the respective same-ligand complexes. We further introduce the concept of structure hardening by ligands, by linking it quantitatively for the first time with the value of the non-radiative decay rate Anrad, and interpret it in terms of the lowest vibrational frequency of the complex. In light of all these concepts and results, we conclude that luminescence can be boosted in europium complexes by increasing ligand diversity, which, in turn, should be ideally obtained with the help of hardener ligands. This general and comprehensive strategy aims at increasing Arad while simultaneously decreasing Anrad.

Faster Synthesis of Beta-Diketonate Ternary Europium Complexes: Elapsed Times & Reaction Yields.

β-diketonates are customary bidentate ligands in highly luminescent ternary europium complexes, such as Eu(β-diketonate)3(L)2, where L stands for a nonionic ligand. Usually, the syntheses of these complexes start by adding, to an europium salt such as EuCl3(H2O)6, three equivalents of β-diketonate ligands to form the complexes Eu(β-diketonate)3(H2O)2. The nonionic ligands are subsequently added to form the target complexes Eu(β-diketonate)3(L)2. However, the Eu(β-diketonate)3(H2O)2 intermediates are frequently both difficult and slow to purify by recrystallization, a step which usually takes a long time, varying from days to several weeks, depending on the chosen β-diketonate. In this article, we advance a novel synthetic technique which does not use Eu(β-diketonate)3(H2O)2 as an intermediate. Instead, we start by adding 4 equivalents of a monodentate nonionic ligand L straight to EuCl3(H2O)6 to form a new intermediate: EuCl3(L)4(H2O)n, with n being either 3 or 4. The advantage is that these intermediates can now be easily, quickly, and efficiently purified. The β-diketonates are then carefully added to this intermediate to form the target complexes Eu(β-diketonate)3(L)2. For the cases studied, the 20-day average elapsed time reduced to 10 days for the faster synthesis, together with an improvement in the overall yield from 42% to 69%.