Luminescence quenching of tris(2,2′-bipyridine)ruthenium(II) by phenol and dichlorophenols in sol-gel-processed spin-coated thin films

Abstract

The luminescence spectral behaviour of the ruthenium(II)-tris-1,2-bipyridine ion (Ru(bpy)32+) included in organically modified silicate gel matrixes, and the luminescence quenching by phenol and dichlorophenols were investigated. The chloro-derivatives were 2,4-, 2,5- and 2,6-dichlorophenol. Sol-gel technology was used to prepare the “sol” with the precursor methyltriethoxysilane. Coating thin films were obtained from the “sol” by spin coating on glass slide. The Ru(bpy)32+ luminescence quenching experiments were carried out with the quencher in aerated aqueous solution at pH 12 in contact with the film. It was possible to observe an important blue shift in the Ru(bpy)32+ emission spectrum included in the films with respect to the aqueous solution. The quenching plots obtained showed a downward curvature. These plots could be fitted satisfactorily by a sum of two terms of Stern-Volmer with quenching constants KSV1 and KSV2 associated to two different binding sites of the ruthenium complex, which indicates the presence of a matrix microheterogeneity in the films. The KSV1 and KSV2 values and the corresponding fractions of the total emission f01 and f02 for both sites in the films suggest that only a low percentage of the probe is accessible to the quencher and that the probe is efficiently quenched in one of the sites. This site of the probe was assigned to the Site 1 in the results analysis. The value of its respective constant, KSV1, was higher than the value of the constant KSV in homogeneous aqueous solution for the studied quenchers, phenol and dichlorophenols.