Sondando estados fundamentais e eletronicamente excitados de compostos indólicos com potencial ação herbicida

Abstract

In this work, a study was conducted on a series of indole derivatives that presented herbicide action. The density functional theory (DFT) and its TD-DFT formalism were used to investigate the fundamental and excited states, respectively. Employing functional M06-2X and CAM-B3LYP with the aug-cc-pVTZ basis set. With the calculations being performed in gaseous, aqueous phase and dimethyl sulfoxide. In principle, it was observed that solvation decreases excitation energies for almost all compounds, in addition to indole derivatives having lower excitation energies than the indole molecule. For example, the first excited singlet state of the compound 6-chloro8-nitro-2,3,4,9-tetrahydro-1H-carbazole (15a) was found at 3.45 eV while the corresponding state of the Indole was located at 5.0 eV, both determined at the TDDFT/M06-2X/aug-cc-pVTZ level in water. In addition, compounds 15a, 5-chloro-2,3- dimethyl-7-nitro-1H-indole (15b), 6-chloro-2,3,4,9- tetrahydro-1H-carbazole (3b) and 2,3-dimethyl-1H-indole-7-carboxylate ethyl (20b) showed more states likely to be accessed (GOS > or ≅ 0.1 in TD-DFT/M06-2X/aug-cc-pVTZ in water). The occurrence of several excited states accessible at low energies may be indicative of the interaction of chlorophyll with solar radiation, such a factor may harm the photosynthetic process of the plant. The analysis of frontier orbitals suggested the increase in electronic relocation (originated by structural modifications) as being responsible for the decrease of excitation energies.