Hn. Ghosh et al., DIRECT OBSERVATION OF ULTRAFAST ELECTRON INJECTION FROM COUMARIN-343 TO TIO2 NANOPARTICLES BY FEMTOSECOND INFRARED-SPECTROSCOPY, JOURNAL OF PHYSICAL CHEMISTRY B, 102(34), 1998, pp. 6482-6486
Transient infrared (IR) absorption of injected electrons in colloidal
TiO2 nanoparticles in the 1900-2000 cm(-1) region are measured by femt
osecond IR spectroscopy. The direct detection of electrons in the nano
particles with subpicosecond time resolution provides a new approach t
o study ultrafast interfacial electron transfer between semiconductor
nanoparticles and molecular adsorbates. The dynamics of electron injec
tion from sensitizers to nanoparticles and the subsequent back-transfe
r and relaxation dynamics of the injected electrons correspond to the
rise and decay of the transient IR signal of injected electrons. Using
this technique, the injection time for coumarin 343 sensitized TiO2 n
anoparticles in D2O is determined to be 125 +/- 25 fs. The subsequent
decay dynamics of the injected electrons in nanoparticles are found to
be different from conduction band electrons in a bulk TiO2 crystal.