Estudo Foto- e Solvatocrômico de Complexos de Lantanídeos com Espiropirano

Abstract

In this study, coordination complexes comprising the entire series of trivalent lanthanide ions (La³⁺ to Lu³⁺, except Pm³⁺) were synthesized and characterized, employing a derivative of the spiropyran molecule named: 3-(3',3'-dimethyl-6-nitrospiro[chromene-2,2'-indolin]-1'-yl)propanoic acid(SPCOOH), as the ligand. Structural characterization was conducted using vibrational spectroscopy in the infrared (FTIR) and Raman spectroscopy, with the results providing evidence that metal coordination occurs through the oxygen atoms of the carbonyl group and the phenolate moiety of the merocyanine isomer, as indicated by bathochromic shifts. UV-Vis spectroscopic analyses revealed hypsochromic shifts in the absorption bands of the complexes relative to the free ligand, supporting the formation of the complexes and corroborating the vibrational spectroscopy findings. Mass spectrometry analyses indicated the formation of complexes containing two or three ligand molecules per metal center, in addition to water molecules and nitrate ions within the coordination sphere. Stability kinetics studies performed in acetonitrile demonstrated that the complexes exhibit good stability, with no evidence of complete dissociation over the analysis period. Solvatochromism experiments carried out in linear chain alcohols (methanol, ethanol, 1-propanol, 1-butanol, and 1-octanol) revealed a trend of decreasing maximum absorption wavelength with increasing atomic number of the lanthanides, although no direct correlation with solvent polarity was observed. Finally, all complexes exhibited fluorescence, with similar emission profiles attributed to the influence of the SPCOOH ligand. This work provides unprecedented insights into the structural and electronic properties of lanthanide complexes with spiropyran derivatives, thereby expanding the current understanding of the coordination chemistry of these elements and highlighting their potential applications in optical materials and molecular sensors.