Estudo de compostos de coordenação de samário contendo ligante β-dicetonato

Abstract

Luminescent materials have attracted great interest from the scientific community due to their application in optical devices such as Organic Light-Emitting Diodes (OLEDs), a technology widely studied and improved in recent years. It is known that part of the composition of these devices can be composed of thin luminescent film, for example those which use coordination compounds containing lanthanides (Ln3+) as the metal center; these exhibit monochromatic emission and high quantum efficiency when photo or electro-excited. An important mechanism to excite the Ln3+, called the antenna effect, is obtained by transferring energy from the Triplet (T) of the ligand to the levels emitting the metal. A class of ligand that has shown to be efficient in this process of sensitization are the β-diketones (β-dic), these may form, among others, compounds of the general formula [Ln(β-dic)3(H2O)2]. In order to intensify the emission, coordinated water molecules that suppress the luminescence can still be replaced by other chromophoric ligands (L). In this sense, the objective of this work is to synthesize and characterize samarium coordination compounds of the general formula [Sm(bmdm)3(L)x], where bmdm = butyl methoxydibenzoylmethane and L = 1,10-phenanthroline (phen) and 2,2'bipyridine (bipy), starting from the precursor compound [Ln(bmdm)3(H2O)2] and subsequently obtain films by addition of the poly (ethylene-co-vinyl acetate) (EVA), to study the optical properties and in the attempt to give greater mechanical and thermal resistance to the material. For the synthesis of the complex, a 1: 3 stoichiometric ratio of SmCl3: bmdm was used, the aqueous solution containing the metal was slowly added to the ligand ethanolic solution, previously deprotonated by NaOH (aq) 1 molL-1. The films were prepared by dissolving EVA pellets (0.5 g) in chloroform, 1 or 5% (w / w%) of [Ln(bmdm)3(H2O)2], dissolved in the same solvent, was added to matrix. The stoichiometries were confirmed by CHN and titration, as also predicted by semiempirical models, as being [Ln(bmdm)3(H2O)2], [Ln(bmdm)3phen] and [Ln(bmdm)3bipy] for the compounds. When comparing FTIR spectra of ligand and coordination compounds, displacements in the band referring to the stretching ν(C=O) indicate the coordination of the bmdm ligand to the metal. Absorption spectra in UV-Vis indicate that there has been coordination of phen and bipy ligands, and that there is intense absorption in the ultraviolet region, an interesting feature for applications in optical sensors, for example. Emission spectra (~77K) exhibit fine and intense bands attributed to the transitions of Sm3+ (4G5/2 → 6HJ, J = 5/2, 7/2, 9/2 and 11/2), demonstrating that the ligands act as antennas, transferring energy to the metallic center. The doped polymers maintained the luminescent properties of the compounds, and further studies on this system are being carried out.