Unlocking the potential of 2,1,3-benzoxadiazole-based luminescent liquid crystals

W. D. Freitas, M. S. C. Mazzoni, M. J. S. Matos, and B.R.L. Galvão. 2024. “Predicting molecular crystals of polynitrogen (N6) structures with cage-like geometries using ab initio evolutionary algorithm.” Chemical Physics Letters, 844, Pp. 141262. Publisher's Version Abstract

In this work, we employed Density Functional Theory calculations combined with search techniques based on evolutionary algorithms to predict and characterize crystalline structures composed of nitrogen (N6) cage-like molecules. We found stable molecular crystals and a rich phenomenology associated with their behavior under pressure, including atomic rebonding and semiconductor-metal transitions. This investigation resides in the context of high-energy-density materials, since molecular species containing only nitrogen atoms tend to dissociate into N2 molecules, releasing large amounts of energy.

Alex Milton Albergaria Campos, Amauri Leal, Sinésio Salles, and Paulo Santos Assis. 2024. “Biomass and energy connected with iron and steelmaking.” Tecnologia em Metalurgia, Materiais e Mineração, 21, Pp. 0–0.

Rafael N. Gontijo, Marcus V. O. Moutinho, Ariete Righi, Po-Wen Chiu, Pedro Venezuela, and Marcos A. Pimenta. 2024. “Resonant enhancement of the 2G Raman band in twisted bilayer graphene.” Materials Chemistry and Physics, Pp. 129279. Publisher's Version Abstract

Raman spectroscopy is an extremely useful tool to characterize graphene systems. The strongest Raman features are the first-order G band and the second-order 2D and 2D′ bands, which are the overtones of the double resonance D and D’ bands. However, the 2G band, which is the overtone of the G band, is not usually observed in the spectra of monolayer graphene and of crystalline graphite. In this work, we present an experimental and theoretical investigation of the resonance Raman spectra in twisted bilayer graphene (TBG) with different twisting angles and using several laser excitation energies in the NIR and visible ranges. We observed that the 2G band is enhanced when the incident photons are in resonance with the transition between the van Hove singularities in the density of states of the TBG. We show that the 2G band has three contributions (2G1, 2G2 and 2G3), that are not dispersive by changing the laser excitation energy. We also present theoretical calculations showing that the 2G1 and 2G2 bands are related to combinations of the in-phase (IP) and out-of-phase (OP) vibrations of the atoms in the different layers. The Raman excitation profiles (REPs) of the 2G peaks are upshifted in comparison with the REP of the G band. This behavior was confirmed theoretically using a graphene tight binding model. We conclude that the different resonance behavior comes from the fact that the G band is a first-order process whereas the 2G band is second-order processes giving rise to overall different resonance conditions.

Camila Cavalini, Cesar Rabahi, Caique S. de Brito, Eunji Lee, José R. Toledo, Felipe F. Cazetta, Raphael B. Fernandes de Oliveira, Marcelo B. Andrade, Mohamed Henini, Yuhao Zhang, Jeongyong Kim, Ingrid D. Barcelos, and Yara Galvão Gobato. 2024. “Revealing localized excitons in WSe2/β-Ga2O3.” Applied Physics Letters, 124, 14, Pp. 142104. Publisher's Version Abstract

We have investigated the optical and magneto-optical properties of monolayer (ML) WSe2 on flakes of β-Ga2O3 under high magnetic fields. Remarkably, sharp emission peaks were observed and associated with localized excitons related to point defects. A detailed study of low-temperature photoluminescence (PL) and magneto-PL under high perpendicular magnetic field up to 9 T was carried out. Several sharp emission peaks have shown valley g-factors values close to −4, which is an unusual result for localized excitons in WSe2. Furthermore, some PL peaks have shown higher g-factor values of ≈−7 and ≈−12, which were associated with the hybridization of strain localized dark excitons and defects. The reported results suggest that β-Ga2O3 is, indeed, a promising dielectric substrate for ML WSe2 and also to explore fundamental physics in view of possible applications in quantum information technology.

Marília I. F. Barbosa Javier Ellena Alzir A. Batista André V. Alves, Rafael G. Silveira and Rodrigo S. Corrêa. 2024. “cis and trans isomers of Ru(III)-based complexes with lapachol: X-ray diffractions and DFT theoretical insights.” Molecular Crystals and Liquid Crystals, 768, 5, Pp. 168-179. Publisher's Version

Gabriel H. A. Jorge, Filipe A. Couto, Juliana M. P. Almeida, Victor A. S. Marques, Marcelo B. Andrade, and Cleber R. Mendonça. 2024. “Active Optical Tuning of Azopolymeric Whispering Gallery Mode Microresonators for Filter Applications.” Photonics, 11, 2. Publisher's Version Abstract

Light confinement provided by whispering gallery mode (WGM) microresonators is especially useful for integrated photonic circuits. In particular, the tunability of such devices has gained increased attention for active filtering and lasering applications. Traditional lithographic approaches for fabricating such devices, especially Si-based ones, often restrict the device’s tuning due to the material’s inherent properties. Two-photon polymerization (2PP) has emerged as an alternative fabrication technique of sub-diffraction resolution 3D structures, in which compounds can be incorporated to further expand their applications, such as enabling active devices. Here, we exploited the advantageous characteristics of polymer-based devices and produced, via 2PP, acrylic-based WGM hollow microcylinders incorporated with the azoaromatic chromophore Disperse Red 13 (DR13). Within telecommunication range, we demonstrated the tuning of the microresonator’s modes by external irradiation within the dye’s absorption peak (at 514 nm), actively inducing a blueshift at a rate of 1.2 nm/(Wcm−2). Its thermo-optical properties were also investigated through direct heating, and the compatibility of both natural phenomena was also confirmed by finite element simulations. Such results further expand the applicability of polymeric microresonators in optical and photonic devices since optically active filtering was exhibited.

Ana L.S Moura, Pedro H. Machado, and R.S. Corrêa. 2024. “2,5-diphenyloxazole and 4-pyrrolidinopyridine as conformers to picric acid: Structural characterization coupled with Multivariate Statistical Analysis.” Journal of Molecular Structure, Pp. 137670. Publisher's Version Abstract

In this study, 4-pyrrolidinopyridine (PPY) and 2,5-diphenyloxazole (DPO) were employed as N-heterocyclic derivatives to synthesize novel picrate salts. These salts were subsequently subjected to characterization using infrared spectroscopy, ultraviolet spectroscopy, and single-crystal X-ray diffraction. Comparison of these structures with entries in the Cambridge Structural Database (CSD) and the application of two multivariate statistical analyses, namely Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA), facilitated the differentiation of salts and co-crystals based on the structural behaviors of the picrate molecule. Additionally, Hirshfield Surface Analysis and 2D fingerprint plots were employed to investigate intermolecular contacts. The fluorescence emission spectra revealed that compound 2 has the potential to serve as a probe for turn-off detection of picric acid (PA).

A Gómez, E Chavarriaga, D Coral, VDN Bezzon, Y Pham, SC Yu, and O Morán. 2024. “Assessment of electronic states and local structure of Mn-atoms in nanometric-sized La0. 7Ca0. 3Mn1- x Ni x O3 manganites by means of X-ray-absorption fine structure measurements.” Applied Physics A, 130, 1, Pp. 54.

Mirela R. Valentim, Matheus J. S. Matos, and Mario S. C. Mazzoni. 2023. “B2N2O2: A wide-bandgap two-dimensional semiconductor featuring a zigzag nitrogen array of bonds.” Applied Physics Letters, 123, 9, Pp. 093103. Publisher's Version Abstract

In this work, we apply a combination of theoretical techniques to characterize a two-dimensional material with formula B2N2O2, featuring a zigzag array of nitrogen atoms. We predict its energetic, thermal, and dynamic stability and determine its electronic properties, including band structure and mobility evaluation for a phonon-mediated mechanism. We show that the compound is a wideband-gap semiconductor, with parabolic band edges and with large electron and hole mobilities within the deformation potential approach. We ascribe this result to the existence of electronic channels defined by the zigzag array of nitrogen bonds, which define the edges of both conduction and valence bands. We also propose a mechanism to synthesize the compound based on oxygen functionalization and application of pressure. Finally, we show that the results can be generalized to represent a family of 2D compounds.

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Unlocking the potential of 2,1,3-benzoxadiazole-based luminescent liquid crystals

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