Europium, terbium, and ytterbium 3-(3′-triethoxysilylpropyl)pentane-2,4-dionates. Synthesis and the formation of luminescent sol-gel films

Abstract

3-(3′-Triethoxysilylpropyl)pentane-2,4-dione, (EtO)3SiCH2CH2CH2C[-C(O)CH3]2 (I), was synthesized from 3-allylpentane-2,4-dione, CH2 = CH-CH2-C[-C(O)CH3]2, and triethoxysilane, (EtO)3SiH, in the presence of Speier’s catalyst. The silylation occurred mainly at the terminal C atom of the allyl group. The corresponding europium(III), terbium(III), and ytterbium(III) β-diketonates were synthesized from compound I and appropriate metal isopropoxides and used to obtain transparent sol-gel films containing Eu3+, Tb3+, and Yb3+ cations. The film formation was studied by IR spectroscopy. It was found that moisture causes not only the hydrolysis and condensation of triethoxysilyl groups but also the hydration of the cation of the rare-earth metal. When the terbium complex was excited at the wavelength of one of the two peaks (230 and 308 nm) in the excitation spectrum, the cation fluoresced intensely at 491, 547, 585, and 623 nm due to the transitions 5 D 4 → 7 F 6, 5 D 4 → 7 F 5, 5 D 4 → 7 F 4, and 5 D 4 → 7 F 3, respectively. All these bands were narrow, the band at 547 nm being most intense. No emission from the organosilicon matrix at 440 nm was observed. The emission spectra of Eu3+-containing films showed, along with the bands at 593, 618, 667, and 700 nm due to the emission from the cation (5 D 0 → 7 F 1, 5 D 0 → 7 F 2, 5 D 0 → 7 F 3, and 5 D 0 → 7 F 4 transitions, respectively), an intense band at 491 nm due to the emission from the matrix.