Direct observation of interfacial hole transfer from a photoexcited TiO₂ particle to an adsorbed molecule SCN^- by femtosecond diffuse reflectance spectroscopy

On the basis of transient absorption spectral measurements in the whole visible region using femtosecond diffuse reflectance spectroscopy, a hole transfer process from photoexcited TiO₂ to an adsorbed molecule SCN^- was elucidated. In a TiO₂ aqueous suspension with KSCN, absorption rise of dimer radical anion (SCN)₂^•- was observed indicating hole transfer. Interestingly, there were two rise components with <1 ps and several 100 ps, which were shorter in lower pH of the solution. Ultrafast hole transfer and subsequent intermolecular geometrical change of a dimmer radical anion are also discussed.