Taking Advantage of Ortho- and Peri-Substitution to Design Nine-Membered P,O,Si-heterocycles**

A family of cyclic phosphine-disiloxane featuring peri-substituted naphthyl(Nap)/acenaphthyl(Ace) scaffolds has been prepared and fully characterized including X-ray structure, which enables a detailed structural analysis. This straightforward synthesis takes advantage of both ortho- and peri-substitution of Nap/Ace-substituted phosphine oxides. The synthetic method allows diversifying the polycyclic aromatic platform (Nap and Ace) as well as the Si substituents (Me and Ph). Despite a strong steric congestion, the P-atom remains reactive toward oxidation or coordination. In particular, Au(I) complex could be prepared. All the compounds display absorption/luminescence in the UV-Vis range. Surprisingly, the P-trivalent derivatives display unexpected luminescence in the green in solid-state.