Emission from the charge transfer state of xanthene dye-sensitized TiO2 nanoparticles: A new approach to determining back electron transfer rate and verifying the marcus inverted regime
G. Ramakrishna et Hn. Ghosh, Emission from the charge transfer state of xanthene dye-sensitized TiO2 nanoparticles: A new approach to determining back electron transfer rate and verifying the marcus inverted regime, J PHYS CH B, 105(29), 2001, pp. 7000-7008
Electron injection and back electron transfer dynamics of xanthene dyes ads
orbed on TiO2 nanoparticles have been studied by picosecond transient absor
ption and time-resolved fluorescence spectroscopy. When the xanthene dyes a
re adsorbed on the TiO2 surface, a good fraction of the dye molecules forms
charge transfer (CT) complex with the TiO2 nanoparticle. On excitation of
the above system, electron transfer from dye molecule to nanoparticle takes
place. Electron injection has been observed by direct detection of electro
n in the conduction band of nanoparticle and bleach of the dye as detected
by picosecond transient absorption spectroscopy. The corresponding dynamics
have been determined by monitoring the recovery kinetics of the bleach of
the dye in the visible region. Electron injection in the above systems can
take place in two different ways: (1) through the excited state of the dye
and (2) through direct injection to the conduction band on excitation of th
e charge transfer complex. For the charge transfer complex, when the recomb
ination reaction takes place, charge transfer (CT) emission has been observ
ed, Monitoring the CT emission, we have determined the back ET rate. We hav
e also found that the back ET rate for the xanthene dye-sensitized TiO2 CT
complex decreases as the relative driving force increases. Assuming a negli
gible change in electronic coupling, our results provide the evidence for t
he Marcus inverted region kinetic behavior for an interfacial ET process.