Estudo computacional da estrutura eletrônica de [Cu(Salophen)] e [Ni(Salophen)] com potencial aplicação em sistemas foto-absorvedores

Abstract

This work presents an investigation of the electronic structure of Salophen compounds [Cu(Salophen)] and [Ni(Salophen)] using the DFT (Density functional theory) theory level. The compounds derived from Metal-Salophen, are potential light-absorbing systems. In this sense, this work aimed the theoretical study of the above-mentioned complexes and their applications in solar energy converters, such as Dye-sensitized solar cells. The internal coordinates of [Cu (Salophen)] complex was obtained from the structural refinement obtained using X-ray diffraction. Calculus involving Internal coordinates optimization were carried out, which were verified by monitoring the vibrational modes, which did not show any imaginary frequency. The calculation level used was (CAM-B3LYP and PBE0) and maintaining the same basis set functions (6-311 ++ G (d, p)). For the calculations of vertical excitation energy, the M06-2X was used in addition to the aforementioned functional. The CAM-B3LYP and M06-2X functional agreed on most of the results of TD-DFT calculations. However, the functional PBE0 presented satisfactory results, since it followed the trend of the other functional, which have more refined implementation. Finally, the nature of each excited state was explored at the CAM-B3LYP / 6-311 + G (d, p) level through the NTO (Natural Orbital Transition) method, which generates the electron densities of the particle / hole pair. The electronic structure calculations of the [Ni (Salophen)] complex and its free ligand (Salophen) were performed concomitant, due to the lack of internal coordinates obtained by crystal refinement using X-ray diffraction. The PBE0 / 6-311 ++ G (d, p) performance was maintained in all investigations steps of this system, in view of the satisfactory performance of the PBE0 functional in comparison with others with higher computational cost (CAM-B3LYP and M06-2X). A decrease in the electron absorption energy required to access the first excited state of the system was observed, thus, taking the compound to absorb light energy in a range of the electromagnetic spectrum, more shifted to the visible light. The analysis of the nature of the excited states showed a greater contribution of the intraligant bonds and a simple contribution of the metallic center, which contributes more in the diminution of the ways of freedom of the Salophen, by the effect of stiffening caused by the coordination.