Photo-induced electron transfer at polyelectrolyte-water interface

Abstract

Electron transfer reactions of photoexcited ruthenium(II) complexes with quenching agents were studied by steady-state and time-resolved luminescence spectroscopy in the presence of a new class of polyelectrolytes: Starburst dendrimers. The polymers are spherical in shape with a highly packed hydrophobic shell, in particular three different generations of carboxylate sodium salts with different size and surface charge density were used. The experiments were performed using Ru(bpy)₃ ⁺, Ru(phen) ²⁺₃ as luminescent probes, whereas Co(phen) ³⁺₃ and methylviologen were used as quenchers. Comparative results were obtained for the same redox couples in the presence of micelles having different polar groups. Stern-Volmer constants were obtained from luminescence emission intensities as a function of quencher concentration. The results showed an enormous increase of the quenching efficiency in the presence of Starburst dendrimers compared to micellar solutions. Further information was obtained from analysis of the emission decays of the probes by means of an adequate kinetic scheme. The results showed that electron transfer took place at the Starburst-water interface with a mechanism strongly dependent on the structure of the quencher and the hydrophobicity of the probe.