Estudos computacionais de derivados de naftoquinona empregados como sondas espectroscópicas: cálculos relativísticos, parâmetros cinéticos e termodinâmicos

Abstract

In the world, many diseases, such as cancer, require a rapid diagnosis. Currently, it is well known that the fluorescent spectroscopy is one of the most promising methodologies to this end. In this perspective, naphthoquinone derivatives (ANQ) have demonstrated applications as fluorescent probes. Those compounds exhibit excited-state intramolecular proton transfer (ESIPT), which is the main mechanism responsible in their use as fluorescent probes. In this work, the ESIPT process for ANQ was performed at the TD-DFT/CAM-B3LYP/DGTZVP and DFT/B3LYP/DGTZVP level for the electronic and geometric studies, respectively. These parameters were selected for the PCA analysis. The solvent effect was evaluated, and the ESIPT process of ANQ was favorable in nonpolar and polar solvents. Furthermore, the thermodynamics properties showed that the ESIPT is favorable with a proton transfer equilibrium constant of ~105. Naphthoquinone and their halogenated derivatives have fluorescent properties and the presence of such substituents promote changes in the spectroscopic properties of the compounds. Relativistic effects such as spin–orbit coupling, the Hamiltonian relativistic and the basis set including relativistic corrections are essential for the accurate calculation of spectroscopic properties. For the selection of which of these factors, it was employed the factorial design of the 3 3 type, known as a Box–Benhken design, in the halogenated derivatives naphthoquinone (F, Cl, Br and I). For the results, it was observed that the derivatives compounds containing Cl, Br and I do not have the ESIPT process. The compound containing F showed the process, it having 4.69 eV for absorption energy, −1.58 eV for the proton transfer energy and 1.87 eV for the emission energy. Finally, the PCA techniques have been employed for analysis the similarity between 36 naphthoquinone (ANQ) derivatives according to the energies involving in ESIPT process. Our findings point out that substituents with higher electron density promote wavelength red-shifting. In fact, the substituent effects provide an understanding about behavior of the ESIPT process in ANQ derivatives, and how kinetic and thermodynamic parameters can be influenced.