Luminescence quenching of tris (2,2'-bipyridine) ruthenium (II) by 2,6-dimethylphenol and 4-bromo-2,6-dimethylphenol in sol-gel-processed silicate thin films

摘要

The luximescnece properties of tris (1,2-bipyridine) ruthenium (II) (Ru(bpy)_3~(2+)),included in different organically modified silicate gel matries were investigated.Spin and dip-coated thin films were prepared form methyltrimethoxysilane (MTMOS) and methyltriethoxysilane (MTEOS).A blue shift in the emission spectrum of the MLCT excited state of Ru(bpy)_3~(2+) with respect to the aqueous solution was observed in all the films,practically independent of the reaction pH used to prepare the "sol," silane-derived precursor,and procedure used (dip-coating or spin-coating) to obtain the film.A bimodal distribution of probe sites in the films was obtained from modeling of the emission principally on the thermal treatment used in the processing of the films.The lifetimes decreased with the increase in the drying temperature of the films;at the same time,the emission spectra showed a red shift and the luminescence efficiency decreased.A luminescence quenching of the ruthenium complex in the films by 4-bromo-2,6-dimethylphenol and 2,6-dimethylphenol in aerated aqueous solution at pH 12 in contact with the film was also observed.The quenching plots obtained from luminescnece intensities or luminescence intensity decay measurements showed a downward curvature.These plots could be fitted satisfactorily by a sum of two Stern-Volmer terms with quenching constants K_(SV1) and K_(SV2) associated with two differnet binding sites of the ruthenium complex.This result is indicative of the matrix microheterogeneity in the films and is fully consistent with the biexponential nature of the luminescnece intensity decay profiles.The Stern-Volmer parameter values for both sites in the films suggest that ony a low percentage of the probe is accessible to the quencher and its respective constant K_(SV1) is lower than in water.