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Development and implementation of theoretical methodologies for the study of luminescent systems

2026-07-30T00:00:00Z

Title: Development and implementation of theoretical methodologies for the study of luminescent systems Authors: Silva, Gustavo de Santana Abstract: Accurate prediction of excited state energies is extremely important for studies in various fields. In lanthanide complexes, calculations for determining excited states are generally performed using ab initio methods, TDDFT, or the semi-empirical INDO/S-CIS method. The first two cases are limited to systems containing a few dozen atoms. Although capable of handling large molecules, the semi-empirical quantum INDO/S-CIS method exhibits high errors when excitation window adjustment is not performed. Thus, we propose two parameterizations of CIS methods based on the INDO and NDDO approximations, named INDO/S-CIS2 and NDDO/S-CIS, for calculating the singlet and triplet excited state energies of systems containing lanthanide ions. To validate the methods, we compared the results obtained against TDDFT methodologies, based on a benchmark study, and INDO/S-CIS. Both developed methods presented errors smaller than or equivalent to those of the TDDFT methodologies. The error ranges for INDO/S-CIS2 and NDDO/SCIS were 10.43 ± 9.53 and 9.52 ± 7.13, respectively, for the singlet energy, in a set of 41 structures. For the triplet energy, in a set of 87 structures, the error ranges were 9.46 ± 6.88 and 7.68 ± 5.65, respectively. Furthermore, we also present the second version of the LUMPAC software with the incorporation of new methods and resources. Methods for calculating Judd-Ofelt intensity parameters from the excitation spectrum were implemented, as well as a methodology for calculating energy transfer rates for Tb3+ compounds. A novel module for visualizing molecular orbitals was also introduced, facilitating the characterization of excited states centered on the ligands involved in the energy transfer process and the interpretation of the theoretical absorption spectrum. The molecule viewer was optimized. The corresponding Jablonski diagram is generated automatically. In addition, code improvements have been made.

Avaliação de biocarvões na miniaturização da MSPD para determinação de resíduos de pesticidas em alimentos para bebês

2026-07-30T00:00:00Z

Title: Avaliação de biocarvões na miniaturização da MSPD para determinação de resíduos de pesticidas em alimentos para bebês Authors: Nascimento, Roseane dos Santos Abstract: Commercially available foods based on fruits, vegetables, meat and cereals are offered to babies from the age of six months chemical such as pesticides are used in crop cultivation to boost production meeting market demand and controlling pests that hinder plant and fruit growth. Residues of these compounds can remain in the final product and potentially affect a baby’s health; consequently, analytical methods are developed to detect contaminants in various samples. The use of miniaturized methods emerged as a way to reduce solvent volume and the amounts of adsorbents, as well as to eliminate steps compared to conventional method. Thus, this study aimed to develop a miniaturized MSPD method using pipette tips to extract the pesticides abamectin, acephate, acetamiprid, azoxystrobin, bifenthrin, clothianidin, difenoconazole, dimethoate, epoxiconazole, flutriafol, imidacloprid, lufenuron, malathion, methomyl, permethrin, pyraclostrobin, teflubenzuron, thiacloprid, thiamethoxam and thiophanate – methyl from pasty baby foods, in conjunction with liquid chromatography and DAD/UV-Vis detection. Commercial adsorbents C18, sílica gel, PSA, florisil, neutral alumina and the synthetic adsorbent TEOS were tested, as were solventes including methanol, acetonitrile, and mixtures with dichloromethane and ethyl acetate, evaluated at various volumes and ratios. The optimal extraction conditions involved using 40 mg of sample (fortified at 1 µg mL 1 ), 60 mg of sílica gel and 1000 µL of MeOH:ethyl acetate (50:50 v,v), yielding recoveries between 70 – 108 %. Subsequently, the parameters of the sample preparation method using corn cob biochar the adsorbent material that proved most efficient for analyte extraction under the same conditions previously established for sílica, but employing MeOH for analyte elution recovery rates ranged from 62 % to 112 %. Finally, the two methods developed in this study were validated by evaluating the parameters of linearity, sensitivity, selectivity, limit of detection, limit of quantification, accuracy, and precision. Subsequently, the methods were applied to samples of different brands and compositions marketed in Sergipe, but the pesticides under study were not found.

Investigação teórica de complexos luminescentes de eu3+: elucidação dos mecanismos de transferência de energia e desenvolvimento de um protocolo computacional para predição do rendimento quântico

2026-07-27T00:00:00Z

Title: Investigação teórica de complexos luminescentes de eu3+: elucidação dos mecanismos de transferência de energia e desenvolvimento de um protocolo computacional para predição do rendimento quântico Authors: Rodrigues, Jocelia Silva Machado Abstract: This work aimed to theoretically investigate the luminescent propertiesof Eu3+complexes containing β-diketonate ligands, focusing on understandingtheenergytransfer and backtransfer mechanisms responsible for the luminescent efficiencyofthese systems. Using semi-empirical methodologies, four complexes withpotential technological applications were studied: [Eu(tta)3(5,5’-dmbpy)] and [Eu(btfa)3(5,5’-dmbpy)], applied in the construction of OLED devices, and [Eu(tta)3(δ-val)(H2O)] and[Eu(btfa)3(δ-val)(H2O)], investigated as luminescent markers for gunshot residue.The theoretical investigation of these systems was necessary to understand, at themicroscopic scale, the photophysical processes that govern the luminescentperformance of the complexes, allowing them to be correlated withtheoptical properties observed experimentally. The theoretical results obtained agreedwell withthe experimental data provided by collaborators, demonstrating that thecalculatedproperties consistently describe the luminescent behavior of the studiedcompoundsand explain their efficiency in different technological applications. Inadditiontophotophysical studies, this thesis also involved the development of anewcomputational protocol for predicting the quantum yield in Eu 3+ complexes. Themodel was parameterized and validated using experimental quantumyield dataavailableinthe literature for a library composed of 17 Eu 3+ complexes. The results demonstratedhigh accuracy in reproducing the experimental quantum yields, presentingameanabsolute error of around 10%, a value significantly lower than those observedfortheanalytical models traditionally employed in the literature, whose mean errorsrangedbetween approximately 20% and 55%. Thus, this work contributes to theelucidationof the photophysical mechanisms of Eu 3+ complexes and presentsanewcomputational methodology for the precise prediction of quantumyield.

Crescimento e caracterização de monocristais das famílias RCuGa3 (R = Ce, Pr, Nd, Gd) e RNiIn4 (R = La, Ce, Pr, Nd) por meio do método de fluxo metálico: estudos estruturais, magnéticos e do campo elétrico cristalino

2025-08-27T00:00:00Z

Title: Crescimento e caracterização de monocristais das famílias RCuGa3 (R = Ce, Pr, Nd, Gd) e RNiIn4 (R = La, Ce, Pr, Nd) por meio do método de fluxo metálico: estudos estruturais, magnéticos e do campo elétrico cristalino Authors: Possidonio, Daykson Neves Abstract: This work presents a systematic experimental study on the synthesis, structural characterization, and investigation of the magnetic properties of single crystals belonging to two families of rare-earth-based intermetallic compounds, RCuGa3 (R = Ce, Pr, Nd, Gd) and RNiIn4 (R = La, Ce, Pr, Nd). The single crystals were grown using the high-flux method, employing gallium (Ga) and indium (In) as solvents for the RCuGa3 and RNiIn4 series, respectively, enabling the growth of samples with high crystalline quality. Structural characterization was performed by X-ray diffraction (XRD), with crystallographic parameters refined using the Rietveld method implemented in the DBWS software, revealing that the RCuGa3 compounds crystallize in a tetragonal structure with space group I4/mmm, whereas the RNiIn4 compounds adopt an orthorhombic YNiAl4-type structure belonging to the Cmcm space group. Complementary scanning electron microscopy (SEM) analyses, particularly for PrNiIn4, confirmed the chemical homogeneity and high structural quality of the crystals, in good agreement with the XRD results. The magnetic properties were investigated through temperature-dependent magnetic susceptibility measurements for both families, and through specific heat (Cp) measurements for the RNiIn4 series, revealing antiferromagnetic behavior at low temperatures, with magnetic transitions characterized by N´eel temperatures (TN ) ranging from 2.2 K to 9.3 K, namely TN ≈ 3 K (Ce), 4.4 K (Pr), 2.2 K (Nd), and 9.3 K (Gd) for the RCuGa3 series, and 2.8 K < TN < 4.2 K for the RNiIn4 series. The analysis of the inverse magnetic susceptibility in the paramagnetic regime, based on the Curie-Weiss model, allowed the determination of the Curie-Weiss temperature (θCW), the experimental effective magnetic moment (µexp), and the magnetic frustration factor (f), revealing a pronounced magnetic anisotropy in the RNiIn4 series, expressed by ratios χeasy/χhard > 1, which is attributed to the significant influence of crystalline electric field (CEF) effects. Similar CEF-related effects were also identified in the RCuGa3 series, particularly for the Ce- and Pr-based compounds, influencing both the values of TN and the deviations observed from the scaling behavior predicted by the De Gennes rule. The specific heat measurements corroborated the magnetically determined transition temperatures and further reinforced the central role of CEF effects in defining the magnetic ground state of these systems, providing, overall, a comprehensive comparative analysis of the correlations between crystal structure, electronic interactions, and magnetic properties in rare-earth intermetallic compounds.