Karina Silva da Dias, Ranylson Marcello Leal Savedra, Carlos Eduardo Tavares de Magalhães, and Melissa Fabíola Siqueira. 2020. “Solvent influence on molecular interactions in the bulk of fluorene copolymer films.” RSC Adv., 10, Pp. 20772-20777. Publisher's VersionAbstract
The effect of intermolecular interactions between the chains of the amorphous PFO–MEH-PPV films built from toluene and tetrahydrofuran (THF) were studied by atomistic molecular dynamics simulations, applying a successive solvent removal procedure. In the good solvent toluene, the incidence of topological entanglements is more significant. While in the poor solvent, coplanar interactions between neighbouring segments of the chains were also found, which is characteristics of cohesional entanglements. Structure factor curves of the films showed three peaks associated with the microstructure of the film, as previously reported by WAX diffractogram measurements. Moreover, the good solvent promotes more flexibility in dihedral angles, and the chains become nearer to each other.
Tiago E. A. Frizon, André A. Vieira, Fabricia N. da Silva, Sumbal Saba, Giliandro Farias, Bernardo de Souza, Eduardo Zapp, Michell N. Lôpo, Hugo C. de Braga, Felipe Grillo, Sergio F. Curcio, Thiago Cazati, and Jamal Rafique. 2020. “Synthesis of 2,1,3-Benzoxadiazole Derivatives as New Fluorophores—Combined Experimental, Optical, Electro, and Theoretical Study.” Frontiers in Chemistry, 8, Pp. 360. Publisher's VersionAbstract
Herein, we report the synthesis and characterization of fluorophores containing a 2,1,3-benzoxadiazole unit associated with a π-conjugated system (D-π-A-π-D). These new fluorophores in solution exhibited an absorption maximum at around  419 nm (visible region), as expected for electronic transitions of the π-π* type (ε  2.7 × 107 L mol−1 cm−1), and strong solvent-dependent fluorescence emission (ΦFL  0.5) located in the bluish-green region. The Stokes' shift of these compounds is ca. 3,779 cm−1, which was attributed to an intramolecular charge transfer (ICT) state. In CHCl3 solution, the compounds exhibited longer and shorter lifetimes, which was attributed to the emission of monomeric and aggregated molecules, respectively. Density functional theory was used to model the electronic structure of the compounds 9a–d in their excited and ground electronic states. The simulated emission spectra are consistent with the experimental results, with different solvents leading to a shift in the emission peak and the attribution of a π-π* state with the characteristics of a charge transfer excitation. The thermal properties were analyzed by thermogravimetric analysis, and a high maximum degradation rate occurred at around 300°C. Electrochemical studies were also performed in order to determine the band gaps of the molecules. The electrochemical band gaps (2.48–2.70 eV) showed strong correlations with the optical band gaps (2.64–2.67 eV).
Elida Betania Ariza Paez, Sergio Curcio, Natália Neme, Matheus Matos, Rodrigo S. Correa, Fabio Junio Pereira, Flaviane Francisco Hilário, Thiago Cazati, and Jason Guy Taylor. 2020. “Synthesis, Photophysical and Electrochemical Properties of Novel and Highly Fluorescent Difluoroboron Flavanone β-Diketonate Complexes.” New J. Chem., Pp. -. Publisher's VersionAbstract
Difluoroboron β-diketonates complexes are highly luminescent with extensive properties such as their fluorescence both in solution and in solid state and their high molar extinction coefficients. Due to their rich optical properties, these compounds have been studied for their applications in organic electronics such as in self-assembly and applications in biosensors, bio-imaging and optoelectronic devices. The easy and fast synthesis of difluoroboron β-diketonate (BF2dbm) complexes makes their applications even more attractive. Although many different types of difluoroboron β-diketonates complexes have been studied, the cyclic flavanone analogues of these compounds have never been reported in the literature. Therefore, the present work aims to synthesize difluouroboron flavanone β-diketonate complexes, study their photophysical and electrochemical properties and assess their suitability for applications in optoelectronic devices. The synthesis was based on a Baker–Venkataraman reaction which initially provided substituted diketones, which were subsequently reacted with aldehydes to afford the proposed flavanones. The complexation was achieved by reacting flavanones and BF3. Et2O and in total 9 novel compounds were obtained. A representative difluoroboron flavanone complex was subjected to single crystal X-ray diffraction to unequivocally confirm the chemical structure. A stability study indicated only partial degradation of these compounds over a few days in a protic solvent at elevated temperatures. Photophysical studies revealed that the substituent groups and the solvent media significantly influence the electrochemical and photophysical properties of the final compounds, especially the molar absorption coefficient, fluorescence quantum yields, and the band gap. Moreover, the compounds exhibited a single excited-state lifetime in all studied solvent. Computational studies were employed to evaluate ground and excited states properties and carry out DFT and TDDFT level analysis. These studies clarify the role of each state in the experimental absorption spectra as well as the effect of the solvent.
Débora N. [de Freitas], Bruno H.S. Mendonça, Mateus H. Köhler, Marcia C. Barbosa, Matheus J. S. Matos, Ronaldo J. C. Batista, and Alan B. [de Oliveira]. 2020. “Water Diffusion in Carbon Nanotubes Under Directional Electric Fields: Coupling Between Mobility and Hydrogen Bonding.” Chemical Physics, Pp. 110849. Publisher's VersionAbstract
Molecular Dynamics simulations of water confined in carbon nanotubes subjected to external electric fields show that water mobility strongly depends on the confining geometry, the intensity and directionality of the electric field. While fields forming angles of 0° and 45° slow down the water dynamics by increasing organization, perpendicular fields can enhance water diffusion by decreasing hydrogen bond formation. For 1.2 diameter long nanotubes, the parallel field destroys the ice-like water structure increasing mobility. These results indicate that the structure and dynamics of confined water are extremely sensitive to external fields and can be used to facilitate filtration processes.
Marcelo Fernandes Cipreste, Wagner [da Nova Mussel], Juliana [Batista da Silva], Maria [Betânia Freitas de Marques], Ronaldo Junio [Campos Batista], Pedro Lana Gastelois, Waldemar [Augusto Almeida de Macedo], and Edésia Martins [Barros de Sousa]. 2020. “A new theranostic system for bone disorders: Functionalized folate-MDP hydroxyapatite nanoparticles with radiolabeled copper-64.” Materials Chemistry and Physics, Pp. 123265. Publisher's VersionAbstract

Hydroxyapatite nanoparticles have been investigated as biological agents for the treatment and diagnosis of bone diseases due to their properties, providing high affinity to bone tissues and also due to the possibility to chemically modify the surfaces of these nanoparticles to provide active targeting to bone tumors or other bone disorders. In this work, synthetic hydroxyapatite nanoparticles and their surface modifications with folic and medronic acid were studied. Copper-64 was produced by neutron irradiation in a TRIGA MARK I nuclear reactor, and the functionalized nanoparticles radiolabeled with this radioisotope. The multi-technique characterization includes FTIR, PXRD, TGA, DSC, CHN, Zeta potential, XPS, SEM, TEM, and Gamma spectroscopy. Furthermore, the evaluation of the chemical interaction stability was through leaching tested for efficiency. The results indicate that folic and medronic acids can be covalently bonded to HA surface, producing a new material not yet described in the literature, been stably attached to hydroxyapatite nanoparticle surfaces, able to provide active targeting for bone disorders. The complexation of copper-64 provides high radiochemistry purity, although the specific activity must be improved.