Jb. Asbury et al., Evidences of hot excited state electron injection from sensitizer molecules to TiO2 nanocrystalline thin films, RES CHEM IN, 27(4-5), 2001, pp. 393-406
Electron injection dynamics in dye sensitized TiO2 nanocrystalline thin fil
ms are studied with femtosecond mid-infrared spectroscopy. Three classes of
sensitizer molecules, Ru(dcbpy)(2)(X)(2) (X-2 = 2SCN, 2CN, and dcbpy), Fe(
dcbpy)(2)(CN)(2), and ReCl(CO)(3)(dcbpy), are used to examine the dependenc
e of injection rate and yield on the excited state redox potentials. We obs
erved that electron injection occurred on the < 100 fs time-scale and injec
tion quantum yield depended on the redox potential for the series of Ru dye
s. These results suggest that electron injection to TiO2 competes with elec
tronic and vibrational relaxation within the sensitizer excited states and
the branching ratio between these two processes deter-mines the injection q
uantum yield for sensitizer molecules with an excited state redox potential
below the conduction band-edge.