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.