Complexos luminescentes baseados em Tb3+ com alto rendimento quântico

Abstract

In this work, two ligands N,N'-bis(2-hidroxibenzil)-N,N'-bis(piridina-2-ilmetil) etilenodiamina (H2bbpen) and N,N'-bis(2-hidroxilbenzil)-N,N'-bis(piridin-2-ilmetil)1,2- propanodiamina (H2bbppn) were used to prepare luminecent mononuclear complexes: [Tb(bbpen)(NO3)] and [Tb(bbppn)(NO3)]. Ligand H2bbppn differs from H2bbpen by an additional methyl group. Although these ligands are similar, the resulting complexes presented different luminescent properties. In order to evaluate the sensitization efficiency of these ligands at the antenna effect, photoluminescence was studied at room temperature and 11 K, measures of emission, excitation, decay time and quantum yield were performed for both complexes. Results of quantum-mechanical calculations performed for the proligands H2bbpen and H2bbppn showed that both ligands are suitable to work as “antenna” for Tb3+ complexes. [Tb(bbppn)(NO3)] complex showed higher 5D4 (Tb3+) decay time when compared with [Tb(bbpen)(NO3)]. The quantum yield results were (21±2)% and (67±7)% for [Tb(bbpen)(NO3)] and [Tb(bbppn)(NO3)], respectively. Finally, higher quantum yield of [Tb(bbppn)(NO3)] comes from reduced thermally active non radiative paths. Higher non radiative decays occur at the complex I due the bending of the bridging site, this feature is minimized with the methyl group attached to the ethylenediamine at the complex II. Moreover the complex [Tb(bbppn)(NO3)] has lower symmetry when compared with [Tb(bbpen)NO3] and the methyl group form weak bonds with the nitrate group, all these features have impact onto the luminescence properties. Moreover, results of cathodoluminescence showed the 5D4 →7FJ characteristic spectra of Tb3+ that point out the potential of these complexes for application in field emission displays. Both complexes are soluble in acetonitrile (ACN) and dimethyl sulfoxide (DMSO), a characteristic that allowed the processing as thin films. Additionally, a structural change occurs in high concentrated DMSO solution; in this case, the nitrate group was replaced by a DMSO molecule.