Encapsulation of Luminescent Homoleptic [Ru(dpp)3]2+-Type Chromophores within an Amphiphilic Dendritic Environment

Abstract

A new series of homoleptic metallodendrimers has been synthesized through ruthenium-metal complexation by dendritically modified bathophenanthroline ligands. The presence of hydrophilic oligo(ethylene glycol) groups on the surface of the monodisperse metal complexes enabled the solubilization of all of the fractal species in a wide range of solvents, including water. The specific properties of all of these compounds have been systematically investigated by using photophysical techniques as a function of the generation number. Accordingly, the encapsulation of the highly luminescent [Ru(dpp)(3)](2+)-type (dpp=4,7-diphenyl-1,10-phenanthroline) core unit within a dendritic microenvironment creates a powerful means to shield the center from dioxygen quenching. This shielding effect, as exerted on the phosphorescent ruthenium-derived center, is reflected by enhanced emission intensities and extended excited-state lifetimes that are close to the highest values reported so far, even in an air-equilibrated aqueous medium. Interestingly, when inspecting the largest dendritic assembly, that is, the third-generation assembly, significant drops in emission quantum yields and lifetimes are observed. This anomalous behavior has been attributed to the folding of the branches towards the luminescent core.