Estudo teórico da estrutura molecular e propriedades espectroscópicas de complexos polipiridínicos de Ru(II)

Abstract

The study of the photophysical properties of polipyridyl Ru(II) complexes is of great interest in a series of aplications, such as cancer therapy. [Ru(bpy)2(L)]2+ (with L = bpy: 2,2-bipyridine; phen: 1,10-phenantroline; hat 1,4,5,8,9,12-hexaazotriphenilene; dppz: dipyride[3,2-a:2,3-c]phenazine; bpz: 2,2-bipyrazyne; e tap: 1,4,5,8-tetraazaphenantrene) complexes were studied in order to elucidate the role of the ligand and the solvent in their photopysical properties. Calculations within the Density Functional Theory formalism were carried out so as to estimate the electronic properties of the complexes. It has been shown that, in the ground state, the complexes with stronger -donor ligands exhibit a lower Ru-L bonding strength than the ones with stronger -acceptor ligands. The Time Dependent Density Functional Theory was employed to investigate the spectroscopic properties of the complexes. The results have shown that all the complexes have absorption bands in the UV-Vis region with a Metalto-Ligand Charge Transfer (MLCT) band in wavelengths above 300 nm and LigandCentered (LC) bands below that wavelength. A red-shift of the MLCT band was observed for the stronger -acceptor ligands. The solvent effects on these electronic transitions were also evaluated. For the [Ru(bpy)3]2+ complex the first three singlet excited states and the lowest energy triplet state were obtained. The main structural changes of these excited states are related with the elongation of the bonds involving the metallic center and the bipyridine ligands, which indicates a weakening of the bonds in the excited state.