Photophysics of Cage/Guest Assemblies: Photoinduced Electron Transfer between a Coordination Cage Containing Osmium(II) Luminophores, and Electron-Deficient Bound Guests in the Central Cavity.

A heterometallic octanuclear coordination cage [OsZn(L)]X (denoted Os•Zn; X = perchlorate or chloride) has been prepared (L is a bis-bidentate bridging ligand containing two pyrazolyl-pyridine chelating units separated by a 1,5-naphthalenediyl spacer group). The {Os(NN)} units located at four of the eight vertices of the cube have a long-lived, phosphorescent MLCT excited state which is a stronger electron donor than [Ru(bipy)]. The chloride form of Os•Zn is water-soluble and binds in its central cavity the hydrophobic electron-accepting organic guests 1,2,4,5-tetracyanobenzene, 1,4-naphthoquinone and 1-nitronaphthalene, with binding constants in the range 10-10 M, resulting in quenching of the phosphorescence arising from the Os(II) units.