Infrared and Raman Spectroscopic Investigation of Eu3+-Doped and Di-Urethanesil Hybrid Siliceous Materials

The general features of two series of sol-gel derived materials, designated urethanesils (Ut), have been investigated by infrared and Raman spectroscopies with the goal of elucidating the chemical environment of the Eu3+ cations. The host frameworks of the two families of ormolytes studied have been represented by m-Ut(350) and d-Ut(300), where m stands for mono, d stands for di, 350 and 300 are the average molecular weights of the organic precursors (poly(ethylene glycol) methyl ether, PEGME, and poly(ethylene glycol), PEG, respectively). The hybrid matrix of the mono-xerogels is composed by a siliceous backbone bonded by means of urethane linkages (-NHC (=O)O-) to pendant methyl end capped oligopolymer chains with approximately 7 oxyethylene units, whereas that of the di-xerogels is based on a siliceous network grafted through urethane groups to both ends of poly(oxyethylene) segments containing about 6 (OCH2CH2) repeat units. Both classes of materials have been doped with europium triflate (Eu(CF3SO3)(3)). The doped samples have been identified by m-Ut(350)(n)Eu(CF3SO3)(3) and d-Ut(300), Eu(CF3SO3), where n is the molar ratio of (OCH2CH2) repeat units per Eu3+ ion. Materials with n ranging from infinity to 5 have been analyzed. The spectral data obtained provide evidence that the cations begin to coordinate to the ether oxygen atoms of the oligopolymer chains at n = 40 in the mono-urethanesils and at n = 10 in the di-urethanesils. In mono-urethanesils samples with n > 40 and in di-urethanesils materials with n > 10, the Eu3+ coordinate exclusively to the carbonyl oxygen atoms of the urethane linkages.