Estudo de complexos luminescentes derivados do ácido naftóico no estado sólido e em filmes organizados

Abstract

Luminescent compounds containing europium ion (III) are interesting for several applications such as: sensors for bioimaging agents and to optimize/create opticalelectronic devices. In two-dimensional systems the material conformation can be made possible by the design of ligands, in this sense the Langmuir-Blodgett technique stands out for offering structural organization with real-time monitoring during film acquisition. In this work we describe the synthesis and characterization of the amphiphilic complexes [Eu(dion)3(H2O)(DMSO)] and [Gd(dion)3(H2O)(DMSO)], where (dion) is 6-dodecyloxy-2-naphthoic acid. Dion was synthesized in three steps from commercial 6-hydroxy-2-naphthoic acid, through esterification, alkylation and hydrolysis reactions that showed a high yield. The success of the complex synthesis procedure was confirmed by CHN (elementary analysis) and spectral profiles observed by FT-IR. The results obtained by thermogravimetric analyzes reveal high thermal stability (~400 ºC) of the complexes. As for the photoluminescent characteristics, the triplet level of the ligand (T) determined at T = 26 332 cm-1 shows that it acts as an antenna in the energy absorption and transfer process. The photoemission spectra exhibit intraconfigurational transitions characteristic of the Eu3+ ion, with the hypersensitive transition 5D0 → 7F2 at 623 nm being the most intense. The quantum emission efficiency (η) of 40.45% indicates that the long chain of the dion ligand (C12) causes losses by non­radiative processes, in addition to the low value of the Ω2 parameter characterizing a lower covalence of the chemical coordination environment. Above all, the dion ligand, designed to create structured systems, guaranteed the formation of luminescent Langmuir films during complexation at the L-G interface. The photoluminescence spectra monitored in situ in a Langmuir trough showed emission intensification as a function of the compression of the mobile barriers. Luminescent LB films were homogeneously transferred to vitreous substrates. The characteristics of the ligand allow it to act as a surfactant and photo-antenna in organized and two-dimensional systems. The LB technique explored in this work should contribute to advances in the development of sensors for detection of traces of other metals or biological analytes, for example, on a nanostructured surface instead of the traditional solution-based approach.