Ultrafast Dissipation via Interligand Electron Transfer in {Ru(tpy)(bpy)} Chromophores

With the aim of studying interligand electron transfer (ILET) with different driving forces, [Ru(tpy)(R-bpy)(CN)]⁺ complexes with R-bpy = 4,4'-dimethylamino-2,2'-bipyridine (dMAb), 4,4'-dimethoxy-2,2'-bipyridine (dMeOb), 2,2'-bipyridine (bpy) or 4,4'-diethylester-2,2'-bipyridine (deeb) were synthesized and fully characterized using an arsenal of diffraction, electrochemical and spectroscopic techniques together with DFT/TD-DFT calculations. All the compounds studied here undergo ultrafast ILET in the picosecond or subpicosecond time scale, irrespective of the driving force or directionality of ILET, showing a typical Kasha behavior that dissipates energy before any potential bimolecular reactivity. This precludes the utilization of high-energy excited states, involving a non-LUMO excited electron, in solar-energy conversion strategies requiring diffusion-controlled reactivity.