Microenvironment-switchable singlet oxygen generation by axially-coordinated hydrophilic ruthenium phthalocyaninedendrimersElectronic supplementary information (ESI) available: 1H NMR spectra of dendritic pyridine ligands 5-7 and RuP1-3; phosphorescence spectra at 1140 nm of RuP1-3; singlet oxygen luminescence at 1270 nm of RuP1-3 in CHCl3, THF and D2O. See DOI: 10.1039/c0cp01015d

A series of new metallodendrimers built around a ruthenium phthalocyanine core has been prepared. Employing a convergent synthetic strategy, pyridine-containing ligands were prepared and then assembled onto the ruthenium phthalocyanine through axial ligand coordination. The growing shell of oligoethylene glycol chains surrounding the lipophilic core allows solubilisation in water. Photophysical studies show that all the metallodendrimers are strongly phosphorescent and the deactivation pathway of their triplet state depends on the medium in which the compounds are dissolved. On one hand, quenching of the triplet state by the dendritic shell is observed and found to be substantially enhanced in aqueous media. On the other, the dendrimer shields the phthalocyanine from oxygen. This notwithstanding, the phthalocyanines are able to generate singlet oxygen in less polar environments such as in CHCl 3 or THF solution, while in water the generation of singlet oxygen is almost completely switched off. The ability of a series of amphiphilic ruthenium phthalocyanine dendrimers to produce singlet oxygen is governed by the mircoenvironment.