Browsing by Author "Zapp, Eduardo"

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    Strongly luminescent and liquid-crystalline π-conjugated 2-methyl[1,2,3]benzotriazoles with a linear donor-acceptor-donor structure.
    (2020) Silva, Elias Regis da; Hinojosa, Abad Roger Castillo; Eccher, Juliana; Tonet, Michele Duarte; Brondani, Daniela; Zapp, Eduardo; Curcio, Sergio Fernando; Postacchini, Bruna Bueno; Cazati, Thiago; Vieira, André Alexandre
    Symmetrical 2-methyl[1,2,3]benzotriazole (BZT) derivatives with elongated peripheral units connected via acetylenic triple bonds present calamitic thermotropic mesomorphism with nematic and smectic phases. They show intense photoluminescence with near-unity quantum yields in solution. The peripheral groups significantly influence the excited-state lifetime. Fluorescence quenching is observed in the presence of C60, testifying of charge transfer to the fullerene acceptor. The varying sterical demand of the different substituents considerably influences the efficiency of the charge transfer induced fluorescence quenching. HOMO, LUMO and band gap energies ranged from −5.15 to −5.97 eV (ionization potential), −2.47 to −2.96 eV (electron affinity) and 2.68 to 3.08 eV (optical band gap).
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    Synthesis of 2,1,3-Benzoxadiazole derivatives as new fluorophores-combined experimental, optical, electro, and theoretical study.
    (2020) Frizon, Tiago Elias Allievi; Vieira, André Alexandre; Silva, Fabrícia Nunes da; Saba, Sumbal; Farias, Giliandro; Souza, Bernardo de; Zapp, Eduardo; Lôpo, Michell N.; Braga, Hugo de Campos; Grillo, Felipe Fardin; Curcio, Sergio Fernando; Cazati, Thiago; Rafique, Jamal
    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).