Electron Injection Efficiency in Ru-Dye Sensitized TiO₂ in the Presence of Room Temperature Ionic Liquid Solvents Probed by Femtosecond Transient Absorption Spectroscopy: Effect of Varying Anions

We investigated the electron injection efficiency of a Ru-complex dye (N719) sensitized TiO 2 system using femtosecond transient absorption in the presence of two different room temperature ionic liquids (ILs) varying their anionic counterparts (tetracyanoborate [TCB] − and dicyanoamide [DCA] − ), keeping the cationic counterpart (ethylmethylimidazolium [EMIm] + ) invariant. We also investigated the effect of varying IL environments on the metal–ligand charge transfer band of the adsorbed N719 on TiO 2 film using steady state absorption spectroscopy and the effect on cyano stretching frequency of ILs in the presence of TiO 2 films using attenuated total reflectance-IR method. The downshift of conduction band (CB) edge energy of TiO 2 nanoparticles in presence of [EMIm][TCB] IL environment has recently been reported ( J. Phys. Chem. C 2011, 115, 816–822). Based on CB edge energy modulation and transient absorption spectroscopic data, we found that the electron injection efficiency is higher in the N719/TiO 2 system in the presence of [EMIm][TCB] IL environment than in the presence of [EMIm][DCA] IL environment by ∼20%.