Highly homogeneous, transparent and luminescent SiO2 glassy layers containing a covalently bound tetraazacyclododecane–triacetic acid–Eu(iii)–acetophenone complex

Abstract

The preparation of sol–gel glasses is described wherein highly stable Eu(III) centres are anchored to the silica glass upon acidic hydrolysis and by using tetraethylorthosilicate (TEOS) as a silica source. The complex employed is Eu·1 and is obtained from bipartite ligand 1, which features a DO3A macrocycle as a hosting unit for the Eu(III) centre, a methoxy-acetophenone unit as an antenna chromophore, and an alkyl chain bearing one primary hydroxy group (DO3A is 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid). Eu·1 is linked to the forming silica glass through the –OH groups and a uniform distribution of the luminescent centres is obtained, as indicated by results from secondary ion mass spectrometry in-depth profiling. The luminescent efficiency of the Eu(III) centres in the solid matrix is evaluated to be 10%, which is comparable to that of Eu·1 in water solution and of a convenient reference complex, Eu·2 (2 is a ligand featuring the same hosting and antenna functionalities of 1, wherein the –OH residue is replaced by an unreactive group, a benzoylmethyl residue). A discussion is given of the photophysical properties exhibited by the complexes in the film and in solution.