Solvent-dependent intramolecular electron transfer in a peptide-linked [Ru(bpy)(3)](2+)-C-60 dyad

A novel peptide-linked [RU(bpy)(3)](2+)-C-60 dyad is shown to undergo an in tramolecular photoinduced electron transfer in chlorinated hydrocarbons tha t causes quenching of the emission associated to the ruthenium metal-to-lig and charge-transfer excited state. Addition of a strong protic solvent, suc h as hexafluoro-2-propanol, leads to deactivation of the electron-transfer process with concomitant recovery of the emission to the extent recorded fo r a solution of a reference ruthenium complex lacking the fullerene moiety. This behavior is associated with a direct effect of the protic solvent on the secondary structure of the peptide spacer, whose preferred conformation s in solution have been assessed by FT-IR and 2D NMR spectroscopy. Chlorina ted hydrocarbons favor the peptide 3(10)-helical conformation, which provid es efficient interactions between the ruthenium and C-60 chromophores, wher eas the presence of a protic solvent produces helix unfolding, which hamper s suitable spatial orientations of the chromophores for electron transfer. The reversibility of the phenomenon is also demonstrated and discussed.